1999 MRS Spring Meeting & Exhibit

Chairs

Mark DeGuire
Dept of MS&E
Case Western Univ
Cleveland, OH 44106-7204
216-368-6481

Lorraine Francis
Dept Chem Eng & Matls Sci
Univ of Minnesota
151 Amundson Hall
Minneapolis, MN 55455
612-625-0559

Lisa Klein
Dept of Ceramic & Materials Engr
Rutgers Univ
Piscataway, NJ 08854-8065
732-445-2096

James Mark
Chemistry Dept
Univ of Cincinnati
ML-0172
Cincinnati, OH 45221-0172
513-556-9292

Symposium Support

*3M Advanced Materials Technology Center
*Chemat Technology, Inc.
*Dow Chemical Company
*Eastman Kodak Company

Proceedings published as Volume 576
of the Materials Research Society
Symposium Proceedings Series. * Invited paper

SESSION DD1: SYNTHESIS AND PROCESSING I
Chair: Florence Babonneau
Monday Morning, April 5, 1999
Salon 11/12 (M)

8:30 AM *DD1.1
ORGANIC/INORGANIC MOLECULAR HYBRID MATERIALS FROM CUBIC SILSESQUIOXANES. R.M. Laine , C. Zhang, M.C. Gravel, A. Sellinger, N.L. Dias Filho, H. Nyguen, L. Viculis and Q. Zhu, Departments of Materials Science and Engineering, Chemistry, and the Macromolecular Science and Engineering Center, University of Michigan, Ann Arbor, MI.

Octafunctionalized silsesquioxanes [(RSiO_1.5), cubes] offer potential as rigid, hard nanoplatforms to which a variety of organofunctional groups can be appended. In principle it is possible to create octafunctional macromonomers that at the synthetic level are useful as cross-linking agents, building blocks for novel polymeric materials, initiation sites for dendrimer syntheses, etc. In the materials arena, functionalized cubes offer access to nonporous materials, nanoreinforced composites or materials that act as hosts for other molecules, etc. We describe here the synthesis and characterization of several new functionalized cubes and several novel, materials with useful mechanical properties and high temperature stability.

9:00 AM DD1.2
DISCRETE POLYEDRAL Si/O FRAMEWORKS AS PRECURSORS TO HYBRID ORGANIC-INORGANIC THERMOPLASTICS. Frank J. Feher , Frank Nguyen, Daravong Soulivong, Richard Brutchey, Dept of Chemistry, University of California, Irvine, CA; Joseph D. Lichtenhan, Joseph J. Schwab, Hybrid Plastics, Fountain Valley, CA.

Fully condensed polyhedral oligosilsesquioxanes (i.e., [RSiO_3/2]_n) and spherosilicates (i.e., [(R₃SiO)SiO_3/2]_n) are attractive feedstocks for the manufacture of polymerizable Si/O frameworks. This talk will describe several practical methods for producing structurally well-defined Si/O monomers from readily available polyhedral silsesquioxanes and spherosilicates, including R₆Si₆O₉ and R₈Si₈O₁₂ frameworks.

9:15 AM DD1.3
NANOCOMPOSITES OF SILOXANE AND SILSESQUIOXANES WITH DIELS-ALDER POLYMERS. Raef M. Shaltout , Douglas A. Loy, Encapsulation and Foams Department, Sandia National Laboratories, Albuquerque, NM.

In-situ filling through hydrolysis and condensation of silicon alkoxides has been utilized to generate nanocomposites in which the filler phase can be intimately associated with the polymer on relatively small length scales. One problem of the method has been achieving useful fill volumes without bulk phase separation of the reacting silicon monomer from the polymer. In this paper, we describe the preparation of a new class of nanocomposite materials in which the filler phase is pre-assembled before formation of an organic, Diels-Alder polymer. Maleimide monomers, prepared from alkoxysilylpropyl amines and maleic anhydride, were protected against side reactions by forming the oxonorbornene Diels-Alder adduct with furan. The monomers were then reacted under sol-gel conditions to form oligomers or polymers-the filler phase. These materials were then heated in the presence of a co-monomer containing two or more furyl groups, thereby exchanging the more volatile furan protecting group for the furyl co-monomer and creating a composite material. Details of the preparation and characterization of the materials will be given.

9:30 AM DD1.4
CHARACTERIZATION OF ORGANICALLY MODIFIED SILICATES BY ¹⁷O SOLID STATE MAS AND MQ-MAS NMR. Virginie Gualandris, Florence Babonneau , Chimie de la Matiëre Condensée, UPMC-CNRS, Paris, FRANCE; Pierre Florian, Dominique Massiot, CNRS-CRMHT, Orléans, FRANCE.

Hydrolysis and condensation of various organosilanes (RSi(OR')_4-x, R'=Me, Et, x=0,1,2) lead to the formation of hybrid networks in which organic R groups are directly grafted on the silicate network. The spatial distribution of the various Si units in the final gel network depends on the chemical reactivity of the starting monomeric precursors, and will strongly influence the properties of the final materials (mechanical strength, hydrophobicity...). It is thus important to find characterization tools to probe the spatial arrangment of the various sites and this paper will highlight the use of ¹⁷O solid state NMR. Organically modified silicates have been prepared, using methyltriethoxysilane and tetraethoxysilane in various ratios. The final network is thus composed of trifunctionnal T units and tetrafunctionnal Q units. Three types of oxo bridges can be formed through the competitive self-condensation or co-condensation reactions : (T)-O-(T), (Q)-O-(Q) and (T)-O-(Q). ¹⁷O-enriched water was used as reactant in order to selectively enrich the various oxo bridges, and to perform ¹⁷O solid state MAS-NMR. The combination of MAS NMR experiments recorded at two different magnetic fields, and of the recently discovered MQ-MAS experiments allowed us to identify clearly the three types of oxo bridges. Quantitative analysis was then extracted from the MAS-NMR spectra, and compared with calculations based on randomly distibuted Si units.

9:45 AM DD1.5
STORAGE STABILITY OF SOLVENT-FREE CONDENSATES OF FUNCTIONALIZED TRIALKOXYSILANES. Sabine Stein , Stefanie Cramer von Clausbruch, Norbert Moszner, Volker Rheinberger, IVOCLAR AG, Schaan, Principality of Liechtenstein.

The lack of storage stability of organic-inorganic solvent-free sols is a well-known problem. We investigated the influence of different solvents in the acid catalyzed hydrolysis of various sols on their storage stability. Our experiments were founded on two different silanes, 3-methacryloxypropyltrimethoxysilane (MPTS) and 1,1,1-tris(allyloxymethyl)-1-[[[3-(triethoxysilyl)propyl]amino- carbonyl]oxymethyl]methane (Si 31), synthesized by reaction of pentaerythritol triallyl ether and 3-isocyanatopropyltriethoxysilane. The employed solvents were alcohol, tetrahydrofurane and tert.-butyl methyl ether in a range of 30 to 95 in solution. In order to get comparable chemical conditions the degree of condensation of the various sols were adjusted between 75 and 80. Furthermore, the sols were modified by silylation with trimethylchlorosilane. A comparison of the silylated and nonsilylated silanes clearly showed that a decrease in residual silanol groups increase the storage stability. The results of the investigations demonstrated that the storage stability of solvent-free condensates of functionalized trialkoxysilanes depends significantly on the kind and also on the amount of solvent used in hydrolysis.

10:00 AM DD1.6
NEW ORGANIC-INORGANIC POLYMERS USEFUL AS TARGETS IN INERTIAL-CONFINEMENT FUSION EXPERIMENTS. Franck David Quillot, Didier Marsacq , CEA-DAM, Monts, FRANCE; Alain DuchEne, Faculte des Sciences, Laboratoire PIMIR, Tours, FRANCE; Jean Marie Catala, Institut Charles Sadron, Strasbourg, FRANCE.

Original organic-inorganic polymers and copolymers useful as targets in inertial-confinement fusion experiments are under development. Such polymers can be employed to prepare fuel container or targets as form as microballon or polymer foams. The presence of metal atoms such as silicon or germanium is required during experiments to convert laser energy in X-ray energy. The atomic composition of polymers is a relevant parameter. They must be exclusively composed with hydrogen and metal atoms without oxygen or other impurities. Homopolymers and copolymers of styrene and p-functionnalized styrene are prepared by using nitroxide-mediated living free radical polymerization. This polymerization technic allows us to produce microballons exhibiting high sphericity and wall uniformity because of the low molecular weight dispersion. The synthesis and reactivity of p-functionnalized styrene bearing an organometallic function are examined. The physical properties of corresponding polymers are also described.

10:45 AM *DD1.7
SOL-GEL POLYMERIZATION OF ORGANOTRIALKOXYSILANES EFFECT OF THE ORGANIC SUBSTITUENT ON GELATION. Douglas A. Loy , Brigitta M. Baugher, Duane A. Schneider, Encapsulation and Foams Department, Sandia National Laboratories, Albuquerque, NM.

Silsesquioxanes, [RSiO₁.5]_n, are a family of siloxane network polymers that have become important as vehicles for introducing organic functionalities into sol-gel materials. However, there has not been a systematic study of the ability of organotrialkoxysilanes to form gels through the sol-gel process. In this study, we have examined the sol-gel chemistry of a variety of organotrialkoxysilanes (RSi(OR')₃) with different organic groups (R = H, Me, Et, Pr, i-Pr, n-Bu, i-Bu, t-Bu, hexyl, octyl, decyl, dodecyl, hexadecyl, ocatdecyl, cyclohexyl, vinyl, phenyl, benzyl, phenethyl, chloromethyl, cyanoethyl, chloromethylphenyl, aminopropyl) with methoxide or ethoxide substitutents on silicon, at varying monomer concentrations, and with acidic and basic catalysts. In general, three different groups of materials were obtained. Many of the monomers reacted to form crystalline oligomers or polyhedral oligosilsesquioxanes. The majority of the polymerization experiments produced resinous oligomers or polymers. A minority of the polymerization experiments afforded gels. Gels obtained from these polymerizations were processed as xerogels and characterized by solid state NMR, microscopy, and nitrogen sorption porosimetry.

11:15 AM DD1.8
PREPARATION AND PROPERTIES OF INORGANIC-ORGANIC HYBRIDS FROM VINYL- AND 3-METHACRYL- OXYPROPYLTRIMETHOXYSILANE. Norihiro Takamura , Takahiro Gunji, Yoshimoto ABE Department of Industrial Chemistry, Faculty of Science and Technology, Science University of Tokyo, Yamazaki, Noda, Chiba, JAPAN.

Inorganic-organic hybrids have been focused on as a candidate to create a novel material composed of organic and inorganic structures bonded through covalent linkages. Tailoring the hybrids, therefore, are expected to provide multifunctional coating materials with properties such as high transparency, thermal stability, and scratch resistance as well as insulators and dielectrics. The synthetic routes would be sol-gel process or precursor method using silanes or metal organic compounds. Vinyl- and 3- methacryloxypropyltrimethoxysilane (VTS and MAS) are preferable starting materials to prepare polyvinylpolysilsesquioxane (PVPS) and poly-3- methacryloxy- propylpolysilsesquioxane (PMPS), respectively. These can be precursors to not only coating films but also hybrid films to investigate the relationship between the structure and properties of precursor polymers and materials. PVPS and PMPS were prepared by radical polymerization of VTS and MAS, respectively, with t-butyl peroxide at 150C for 2 h followed by acid- catalyzed hydrolysis. Those were transparent and viscous solutions and gave gel films by casting the 20 wt% acetone- methanol solutions of PVPS and PMPS on the polymethylpentene shale at 80C for several days. The gel films thus prepared were highly transparent and flexible. The thickness of PMPS gel films was 0.02 mm. The tensile strength of films was dependent on the degree of polymerization of organic group which was estimated by GPC analysis. When the degree of polymerization of organic group is increased from 10 to 48, the tensile strength is decreased from 9.7 to 3.6 MPa but the film was more flexible. This is the reason why the formation of siloxane bonds was prevented by steri

11:30 AM DD1.9
EFFECT OF METAL ALKOXIDE ADDITION ON HYDROLYSIS AND CONDENSATION REACTIONS OF PHENYLTRIETH- OXYSILANE. Ikuko Yoshinaga , Noriko Yamada, Shingo Katayama, Nippon Steel Corporation, Advanced Technology Research Laboratories, Kawasaki, JAPAN.

Inorganic-organic hybrids containing phenyl groups as an organic component are expected to provide peculiar properties because of the thermal stability and steric effect of phenyl groups. We have incorporated various inorganic components into a phenylsiloxane network derived from phenyltriethoxysilane (PTES) in order to alter the properties of the hybrids in a wide range. Metal alkoxides as an inorganic precursor were found not only to alter the properties, but also to accelerate the condensation reaction of PTES. The ²⁹Si-NMR study revealed that the chemical shifts for T³ were developed by the addition of metal alkoxides into the reaction system of PTES. The acceleration effect was also found to depend on metal alkoxides. Ti ethoxide and Al buthoxide significantly accelerated the condensation reaction as compared with Ta ethoxide. The difference in acceleration of the condensation reaction of PTES is thought to result from the reactivity of metal alkoxides toward hydrolyzed PTES.
Research supported by NEDO, under the Synergy Ceramics Project of the ISTF program promoted by AIST, MITI, Japan.

11:45 AM DD1.10 X-RAY AND NEUTRON SMALL ANGLE SCATTERING INVESTIGATION ON PRECURSOR DERIVED B-C-N CERAMICS. Dieter Heinrich Sauter , Joachim Bill, Universitat Stuttgart, Insitut für Nichtmetallische Anorganische Materialien, Stuttgart, GERMANY; Peter Lamparter, Stefan Schempp, Max-Planck-Insitut für Metallforschung, Stuttgart, GERMANY; Fritz Aldinger, Universitat Stuttgart, Insitut für Nichtmetallische Anorganische Materialien and Max-Planck-Insitut für Metallforschung, Pulvermatallurgisches Laboratorium, Stuttgart, GERMANY.

The synthesis of elementoorganic polymers and their subsequent transformation into inorganic materials by thermolysis is a novel approach to design new materials providing semiconducting properties and high oxidation resistance at high temperatures. Amorphous B₂₈C₄₀N₃₂ ceramics were produced by thermolysis of a polyborcarbodiimide precursor at 1100C in argon gas atmosphere. X-ray wide angle scattering shows that the samples are fully amorphous up to 1600C. In order to investigate the medium range structure of the amorphous ceramics, small angle scattering experiments were performed. For the identification of the scattering centres the methode of contrast variation was employed. This was achieved by combination of small angle X-ray scattering (SAXS) experiments with small angle neutron scattering (SANS) measurements. In order to suppress the influence of surface scattering the immersion technique with suitable mixtures of C₂H₅OH and C₂D₅OD was applied. These experiments revealed, that the amorphous ceramics contain heterogeneities in the order of 20 caused by phase separation in the amorphous matrix. Further on, the temperature dependence of the medium range structure of the samples was investigated. A strong temperature-time dependence is determined considering the Guinier radius of the scattering regions of the annealed samples. Investigations of the crystallisation process during heat treatment up to 2000C suggest the formation of a carbon rich ternary boroncarbonitride phase.
 
 
 

SESSION DD2: SYNTHESIS AND PROCESSING II
Chair: Douglas A. Loy
Monday Afternoon, April 5, 1999
Salon 11/12 (M)

1:30 PM DD2.1
ORGANIC-INORGANIC HYBRID MATERIALS FROM SURFACE INITIATED POLYMERIZATION. Thomas A.P. Seery and Fatma Vatansever University of Connecticut, Chemistry Department and Polymer Program, Storrs, CT.

Organic-inorganic hybrids must overcome the thermodynamic tendency to phase separate. This is an especially urgent issue during processing when it is desirable to disperse nanoscale particles of one component (inorganic) phase throughout a second (organic) phase. Control of the interface between phases becomes a critical issue for the preparation of high performance materials. Silane coupling agents are one means to prepare a silica surface and we have extended this approach by polymerizing from the distal end of such a coupling agent. End functional coupling agents have been used to attach ruthenium alkylidene catalysts for ring opening metathesis polymerization of cyclooctadiene and norbornenes. Polymerization of cyclooctadiene monomers yield 1,4 butadiene chains on silica surfaces that are candidates for dielectric strength enhancers in high voltage applications. Thermogravimetric analysis is used to obtain the ratio of organic to silicate. Thermal desorption GC-MS provides a means of probing surface-bound species. The nanometer dimensions of the silica make it dispersible in solution so that standard methods of synthetic organic chemistry ­ e.g. NMR, IR - may be used to analyze the intermediates. NMR has been particularly useful in observing the shift of the alkylidene proton (18-21 ppm in a proton spectrum) as an indicator of whether the catalyst is bound to the surface or not.

1:45 PM DD2.2
SYNTHESIS AND CHARACTERIZATION OF HYBRID ORGANIC-INORGANIC NANOPARTICLES USING CONTROLLED/LIVING RADICAL POLYMERIZATIONS. Timothy von Werne, Timothy E. Patten , Univ of California at Davis, Dept of Chemistry, Davis, CA.

Recently developed controlled / living radical polymerizations provide the means to prepare a wide range of polymers with narrow molecular weight distributions and accurate control over their final molecular weights. Nanoparticles, depending upon their composition, exhibit novel magnetic, optical, and materials properties that can be ascribed to their small size and large surface areas. The incorporation of nanoclusters into polymeric materials and the ordering of nanoclusters into superlattices or extended periodic arrangements are important steps in exploiting the properties of these unusual materials. Recently, several approaches to preparing well-defined nanocluster-based structures have been reported. These methods involve the use of DNA conjugates, self-organization, and monolayer formation to define the spatial orientation of the nanoclusters. A polymer-based approach to organizing nanoclusters would combine the spatial definition afforded by the aforementioned techniques with the versatile film-forming and mechanical properties of polymers. We have developed a method to prepare novel, well-defined organic-inorganic nanoparticles by integrating the techniques of colloid and nanocluster synthesis with those of newly developed living radical polymerizations. We have synthesized initiators for atom transfer radical polymerization (ATRP) that possess alkoxysilane functional groups. A monolayer of these bifunctional initiators were attached to 60 nm spherical silica particles to yield macroinitiators for ATRP. The attachment of the initiator was confirmed using elemental analysis, TGA, and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. Particle diameters and the unaggregated state of the particles were confirmed in films using SEM and TEM and in solution using dynamic light scattering (DLS). These macroinitiators were used in styrene ATRP to yield nanoparticles with a silica core and polystyrene outer layer. Growth of the polymer from the surface of the nanoparticle was confirmed using kinetics and DLS measurements. These hybrid nanoparticles were cast from organic solvents to yield composite nanoparticle-polymer films.

2:00 PM *DD2.3
DIFFERENT SOLVENT FREE SYNTHETIC ROUTES TO ORGANIC/INORGANIC HYBRID MATERIALS. Jean-Pierre Pascault , Hamid Kaddami, Jean-Franáois Gérard, Institut National des Sciences Appliquées de Lyon, Laboratoire des Matériaux Macromol, Villeurbanne, FRANCE.
 

The sol-gel chemistry in low-temperature conditions can be used to produce organic-inorganic (O/I) materials nanocomposite from i.e. the in-situ formation of silica-rich phase in a polymer matrix. Different solvent free synthetic routes have been proposed : i) hydrolysis and condensation reactions of silane end capped oligomers prepared by one or two stages. The disadvantage of this route is that the concentration of inorganic clusters is generally low, i.e. 2-3 % bw ii) simultaneous hydrolysis / condensation of tetraethoxysilane and polymerization of an organic monomer. The choice of an alcoholic monomer as hydroxyethyl(meth)acrylate, HE(M)A allows to work without any addition of solvent. In this case morphologies having bicontinuous structure can be obtained. iii) polymerization of an organic monomer in presence of preformed functionalized silica nanoparticles (  10nm in diameter). Similar concentrations of inorganic phase but quite different morphologies than case ii) can be prepared in this case. Rheological investigations made during the polymerization of these different systems, display many differences, depending on the synthesis route and the silica content. The morphologies and the phase compositions were studied by means of different techniques. These parameters can be controlled both from the method of synthesis and by changing the acid catalyst concentration of the sol gel chemistry. iv) More recently a quite different synthesis method has been proposed : functionalized polyhedral silsesquioxanes(R Si O1.5)n are first synthesized and then copolymerized with organic monomers or precursors as polyurethane ones.

2:30 PM DD2.4
SOL-GEL CHEMISTRY BY RING OPENING POLYMERIZATION. Douglas A. Loy, Kamyar Rahimian , Encapsulants and Foams Department, Sandia National Laboratories, Albuquerque, NM.

Sol-gel processing of materials is plagued by shrinkage during polymerization of the alkoxide monomers and processing (aging and drying) of the resulting gels. We have developed a new class of hybrid organic-inorganic materials based on the solventless ring-opening polymerization (ROP) of monomers bearing the 2,2,5,5-tetramethyl-2,5-disilaoxacyclopentyl group, which permits us to drastically reduce shrinkage in sol-gel processed materials. Because the monomers are polymerized through chain growth mechanism catalyzed by base rather than the step growth mechanism normally used in sol-gel systems, hydrolysis and condensation products are entirely eliminated. Furthermore, since water is not required for hydrolysis, an alcohol solvent is not necessary. Monomers with two disilaoxacyclopentyl groups, separated by a rigid phenylene group or a more flexible alkylene group, were prepared through disilylation of the corresponding diacetylenes, followed by ring closure and hydrogenation. Anionic polymerization of these materials, either neat or with 2,2,5,5-tetramethyl-2,5-disila-1-oxacyclopentane as a copolymer, affords thermally stable transparent gels with no visible shrinkage. These materials provide an easy route to the introduction of sol-gel type materials in encapsulation of microelectronics, which we have successfully demonstrated.

2:45 PM DD2.5
DENDRIMER-METAL NANOCOMPOSITES. Lajos Balogh , University of Michigan Center For Biologic Nanotechnology, Ann Arbor, MI; Donald A. Tomalia, Michigan Molecular Institute, Midland, MI; Kenneth S. Laverdure and Samuel P. Gido, University of Massachusetts Amherst, Polymer Science and Engineering, Amherst, MA; Andrew G. Mott, Mary J. Miller and Brian P. Ketchel, AMSRL-SE-EO, Gaithersburg, MD.

Dendrimer metal nanocomposites are novel hybride materials that display unique physical and chemical properties as a consequence of the atomic/molecular level dispersion of an inorganic guest within a dendrimer host. In their synthesis, dendrimers are used as templates to pre-organize metal ions followed by an in-situ reduction, which will immobilize and stabilize atomic domains of the reaction product(s). Size, shape, size distribution and surface functionality of these nanocomposites are determined and controlled by the dendritic macromolecules and may also be influenced by the encapsulated compounds. In this work, surface-modified poly(amido-amine) dendrimers were used to prepare Cu(0)-PAMAM, Ag(0)-PAMAM and Au(0)-PAMAM dendrimer-metal nanocomposites containing stable and solvent soluble zero valent metals. Characterization of the resulting nanocomposites has been carried out by TEM, UV-visible spectroscopy, scattering techniques, etc. The role of ion preorganization in the resulting nanocomposite structures as well as their chemical and optical properties will be compared and discussed including potential applications.

3:30 PM DD2.6
POLYMER CRYSTALLIZATION STUDIED IN CONFINED DIMENSIONS. Frank-Dieter Kuchta , Piet J. Lemstra, Dutch Polymer Institute (DPI), Eindhoven, THE NETHERLANDS; Hartmut R. Fischer, TNO-TPD Materials Research & Technology, Eindhoven, THE NETHERLANDS.

The aim of the present study is to link the fundamental research field of polymer crystallization with the technical important field of the preparation and the properties of polymer-layered silicate nanocomposites. It is known that semi-crystalline polymers crystallize in different phases (e. g. monoclinic, hexagonal) forming chain-folded lamellar. Depending on experimental conditions (e. g. temperature, pressure) the crystal size (lamellar thickness) is affecting the stability of these phases. The incorporation of layered silicates acting as hard walls into semi-crystalline polymers opens now new possibilities: i) To study polymer crystallization in confined dimensions; ii) To provide materials from commodity or engineering polymers with new or enhanced properties. From the fundamental work of researchers at Toyota Central Research and Development Laboratories on nanocomposites based on polyamide-6 and layered silicates it became apparent, that polyamide-6 does not crystallize in the monoclinic but in the hexagonal form. This form exhibits advantageous properties (e. g. higher toughness, barrier properties) hence it is of technical interest. Within the present investigation the effect of an external confinement introduced by highly anisotropic silicate layers of organically modified clay minerals on crystal growth and nanocomposite properties has been studied on polyamide-6, polyamide-11, polyethylene and polypropylene. The composites were prepared both by in situ polycondensation and by reactive blending via melt extrusion. All nanocomposites exhibit a homogeneous distribution of individual silicate layers within the host polymer at low clay content. The lamellar thickening growth is reduced in polyamide crystallization due to the external constrained of the silicate layers in the host polymer. In polyamide-11 crystallization a phase transition (triclinic/hexagonal) is expected at higher clay contents. Furthermore the nanocomposite shows an enhanced thermal stability and tensile modulus.

3:45 PM DD2.7
MELT INTERCALATION OF PMMA INTO LAYERED SILICATES. Zhiqi Shen , George P. Simon, Yi-Bing Cheng, Monash Univ., Dept. of Materials Engineering, Clayton, Melbourne, AUSTRALIA.

Organic-inorganic hybrid materials have recently attracted much interest, especially polymer-silicate hybrids. PEO, PS and a series of styrene-dervative polymers were reported to intercalated into layered silicates via melt intercalation. In this study, intercalation of PMMA with various tacticities and molecular weights is attempted via a melt intercalation process. The organic-inorganic nanocomposites are characterized by XRD, DSC, TGA and FTIR. Saturation ratio of polymer to silicate is deduced from severval techniques and the effect of processing and resultent thermal properties of PMMA-silicate hybrids are studied.

4:00 PM DD2.8
MODELING THE INTERACTIONS BETWEEN POLYMERS AND CLAY SURFACES THROUGH SELF-CONSISTENT FIELD THEORY. Anna C. Balazs , Chandralekha Singh and Ekaterina Zhulina, Department of Chemical and Petroleum Engineering, University of Pittsburgh, Pittsburgh, PA.

Using numerical self-consistent field (SCF) calculations, we investigate the interactions between two closely-spaced surfaces and the surrounding polymer melt. Short chains (surfactants) are terminally anchored to each of the surfaces. The coated substrates model orginally-modified clay crystallites (sheets). Through the calculations, we vary the characteristics of the surfactants and polymers to isolate conditions that drive the polymer to penetrate the gap between the surfaces. We also consider the effect of employing end-functionalized chains to promote the dispersion of bare clay sheets within the polymer matrix. We find that this scheme provides a robust method for exfoliating the sheets. To consider this case in greater depth, we develop an analytical SCF theory to model the interactions among the functionalized chains, nonfunctionalized polymers and the clay sheets. The results from the numerical and analytical SCF models show good agreement on the behavior of the system. The results indicate that the optimal polymeric candidates for creating stable exfoliated composites are those that would constitute optimal steric stabilizers for colloidal suspensions.

4:15 PM *DD2.9
NANO AND MICROSCALE PATTERNING OF ORGANIC/INORGANIC FUNCTIONAL COMPOSITES. Ilhan A. Aksay , Princeton University, Department of Chemical Engineering and Princeton Materials Institute, Princeton, NJ.

This presentation will focus on the synthesis and processing of organic/inorganic composites on two distinct length scales: (i) Self-assembly of organic surfactants is used to generate patterns at the 10  to 1 micron length scale; and (ii) field-assisted alignment is used to generate patterns at length scales larger than 1 micron. The utilization of such nanostructured building blocks for the construction of larger, viable composite materials can be accomplished through lamination of thin films and patterning through microcontact printing and electrohydrodynamic (EHD) manipulation of fluids. Extension of these patterning methods to ceramics such as BaTiO₃ and PbOZrO₂TiO₂ (PZT) are of interest for several reasons. First, their high dielectric constants allow them to achieve high capacitances even with thick layers and/or small area. This allows one to overcome a major limitation of some printed insulator work today, where pinhole limitations are a major problem for achieving high capacitances, e.g. in the F range as might be required for de-spiking capacitors in real circuits. Second, ferroelectrics such as BaTiO₃ can be used in non-volatile memory structures and have advantages over conventional MOS types of non-volative memory in many applications. We have patterned dielectric or piezoelectric films (BaTiO₃, PbOZrO₂TiO₂ (PZT), and Pb(Zn1/3Nb2/3)O₃ (PZN) on substrates such as silicon and steel at temperatures below 650C. Electron microscopic characterization of the patterned PZT thin films shows that they can be converted to a single crystalline form where the dimensions of the single crystal are defined by the width and the height of the pattern lines.
 

SESSION DD3: NOVEL ORDERED HYBRID STRUCTURES
Chair: Timothy E. Patten
Tuesday Morning, April 6, 1999
Salon 11/12 (M)

8:30 AM *DD3.1
EVAPORATION-INDUCED SELF-ASSEMBLY OF ORDERED NANOPOROUS AND NANOCOMPOSITE FILMS AND POWDERS. C.J. Brinker , A. Sellinger, Y. Lu, H. Fan, N. Huesing, D. Doshi, N. Doke, G. Lopez and T. Ward, The University of New Mexico, Sandia National Laboratories Advanced Materials Lab, Albuquerque, NM.

Beginning with a dilute, homogeneous solution of ethanol, water, surfactant, and soluble silica, we previously demonstrated the rapid, continuous formation of ordered mesostructured films by dip-coating. Preferential evaporation of ethanol enriches the depositing film in surfactant, water and silica inducing, micellization and further self-organization into a variety of ordered silica-surfactant mesophases (hexagonal, cubic, lamellar). This presentation will provide a brief overview of our evaporation-induced self-assembly approach followed by a discussion of recent work where we extend this approach to prepare hybrid, organic-functionalized silica frameworks as well as metal-silica and (organic) polymer-silica nanocomposites. In the latter example we exploit the amphiphilic nature of surfactant molecules or block copolymers to simultaneously organize inorganic and organic precursors into highly-ordered nanocomposite films and particles in a rapid, evaporation-induced self-assembly process. Finally I will discuss recent work where we combine our self-assembly approach with micro-contact printing or optical lithography to produce patterned mesostructured surfaces. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under Contract DE-AC04-94AL85000.

9:00 AM DD3.2
AEROSOL-ASSISTED SELF-ASSEMBLY OF SPHERICAL, SILICA NANOPARTICLES EXHIBITING HEXAGONAL, CUBIC, AND VESICULAR MESOPHASES. Yunfeng Lu , Hongyou Fan, Aaron Stump, Timothy L. Ward, Thomas Reiker and C. Jeffrey Brinker, University of New Mexico, NSF Center for Micro-Engineered Materials, The Advanced Materials Laboratory, Sandia National Laboratories.

Nanostructured particles exhibiting well-defined pore sizes and pore connectivities (1-, 2, or 3-dimensional) are of interest for catalysis, chromatography, controlled release, and custom-designed fillers, pigments and optical hosts. During the last several years considerable progress has been made on controlling the macroscopic forms of mesoporous silicas prepared by surfactant and block copolymer liquid crystalline templating procedures. Typically interfacial phenomena are used to control the macroscopic form (particles, fibers, or films), while self-assembly of amphiphilic surfactants or polymers is used to control the mesostructure. To date, although a variety of spherical or nearly-spherical particles have been prepared, their extent of order is limited as is the range of attainable mesostructures. We report a rapid, aerosol process that results in solid, completely ordered spherical particles with stable hexagonal, cubic, or vesicular mesostructures. Our process relies on evaporation-induced interfacial self-assembly (EISA) confined to a spherical aerosol droplet. The process is simple and generalizable to a variety of materials combinations. Additionally, it can be modified to provide the first aerosol route to the formation of ordered mesostructured films.

9:15 AM DD3.3
SELF-ASSEMBLY OF MESO-SCALE AND NANO-SCALE PARTICLES AND ITS APPLICATIONS. Younan Xia , Byron Gates, Sang Hyun Park, University of Washington, Department of Chemistry, Seattle, WA.

We have demonstrated a simple and practical method for the assembly of meso- and nano-scale particles into 3-D ordered lattices over relatively large areas. The particles that we have used include silica colloids and polymer latexes with diameters in the range of 50 nm to 50 um. This method provides an effective route to inorganic-organic composite materials with highly ordered 3-D structures. We have used this method to fabricate functional hybrid materials that can be used as tunable optical filters, photonic band gap structures, and 3-D porous membranes.

9:30 AM DD3.4
MONODISPERSE MICRON SCALE TITANIUM DIOXIDE SHELLS ENCAPSULATING POLYSTYRENE SPHERES. Vinothan N. Manoharan , Pingyun Feng, Department of Chemical Engineering, University of California, Santa Barbara, CA; David J. Pine, Departments of Chemical Engineering and Materials, University of California, Santa Barbara, CA.

We present a method of producing monodisperse spherical titanium dioxide shells with diameters on the order of one micron. First monodisperse polystyrene spheres are synthesized by either emulsion or dispersion polymerization. The spheres are then swollen in a uniform and controlled manner by a mixture of organic solvent and titanium alkoxide emulsified in a nonaqueous polar solvent (formamide), so as to prevent hydrolysis of the alkoxide. When water is added to the resulting monodisperse emulsion, the alkoxide gels at the interface between the droplet and the continuous phase, producing a titanium dioxide shell; at the same time the alcohol liberated by gelation changes the solvent quality in the droplet, causing the original polystyrene sphere to precipitate inside the shell. The product, titania shells encapsulating polystyrene spheres, is a strongly scattering monodisperse colloidal suspension. It may be of interest in the production of materials such as photonic crystals operating at optical wavelengths. Because of the relatively low concentration of titanium needed, it may be also of use in the manufacture of coatings and paints. We have applied a similar method to the production of silicon dioxide shells.

9:45 AM DD3.5
FORMATION OF MESOSCOPIC POLYMER DOTS ON SILICON BY RUBBING TRANSFER. Masahito Sano , Junko Okamura, Seiji Shinkai, Chemotransfiguration Project - JST, Kurume, Fukuoka, JAPAN.

Regular arrays of poly(ethylene) deposits, about 10 nm high and 160 nm in diameter, separated by 340 nm, are formed by simply rubbing the polymer plate against the flat surface of silicon. In general, the polymer transfer can be categorized into four situations: no transfer, macroscopic depositions, nanometer-scale depositions with or without oriented dots. There exist ranges of the conditions that the mesoscopic dot formation occur. The substrate temperature must be below and close to the bulk melting point of the polymer. At a given temperature, the rubbing rate must be within a certain range to induce mass transfer. The silicon surface needs to be prepared so that the polymer wets completely. While high and low density polymers showed the analogous results, a low-molecular weight, linear polymer failed to produce mesoscopic dots. This means that viscoelastic properties and wetting characteristics, rather than surface tensions, are important in dot formation.
 

SESSION DD4: STRUCTURE & PROPERTIES OF ORGANIC MONOLAYERS
Chair: Timothy E. Patten
Tuesday Morning, April 6, 1999
Salon 11/12 (M)

10:30 AM *DD4.1
SYNTHESIS OF STRUCTURED ORGANIC/III-V SEMICONDUCTOR INTERFACES VIA SELF-ASSEMBLY WITH CHALCOGENIDE-FUNCTIONALIZED MOLECULES. D.L. Allara , C.A. Mars, Pennsylvania State University, Dept. of Chemistry, University Park, PA; J.M. Tour and W.E. Reinerth, University of South Carolina, Dept. of Chemistry and Biochemistry, Columbia, SC.

The ever-decreasing dimensions of semiconductor device features places increasing demands on developing methods to reduce undesirable effects of surfaces. We have been developing termination chemistry for III-V semiconductor surfaces via robustly bound, densely packed molecular monolayers. In this talk the focus will be on the self-assembly of both simple aliphatic and highly conjugated aromatic molecules containing S-, Se- and Te-bearing functional groups. The range of functional groups studied and the optimum conditions for forming structured monolayers will be discussed. Recent results indicate that the most highly organized films appear to be formed via Se chemistry while Te attachment requires strongly reducing conditions. Current work is being directed towards characterizing the effects of the organic overlayer on the electronic properties of the semiconductor and the chemical stability of the organic/inorganic interface. Current work is also directed towards exploring the suitability of these films as ultrathin electron beam resists.

11:00 AM DD4.2
HOW STRONG CAN BE THE COVALENT ANCHORS OF A POLYSACCHARIDE TO A GLASS SURFACE? Michel Grandbois , Matthias Rief, Hauke Clausen-Schaumann and Hermann Gaub, Lehrstuhl fur Angewandte Physik, Ludwig-Maximilians-University, Munich, GERMANY; Martin Beyer, Inst. fur Physikalische und Theoretische Chemie, Technische Universitaet, Munich, GERMANY.

Recent developments in piconewton instrumentation allow the manipulation of single molecules and measurements of intermolecular as well as intramolecular forces. Using an atomic force microscope (AFM) as force transducer we measured the force required to break a single covalent bond in the surface anchor of a polymer chain which was covalently attached to the AFM tip on one side and to a glass surface on the other side. The polysaccharide amylose was used as polymer spacer, for its characteristic force vs elongation trace, which exhibits a plateau at 275 piconewton, allows to identify rupture events of single molecules. The rupture force observed in our experiments is centered around 1.9 nanonewtons and is due to the breaking of a single covalent bond in the amino-silane surface anchor of the molecule. Furthermore, this force was compare to the force required to pell off a polymer non covalently adsorb to the surface.

11:15 AM DD4.3
INTEGRATING ORGANIC MOLECULES TO SILICON SURFACES:AN EFFICIENT APPROACH BASED ON Si-N AND Si-O LINKAGES. X.Y. Zhu , J.A. Mulder, R.P. Hsung, W.F. Bergerson, University of Minnesota, Department of Chemistry, Minneapolis, MN.

Organic assemblies on silicon surfaces are important to a number of cutting edge technologies: such as micro electromechanical systems (MEMS), integrated chemical or biological sensors, and hybrid organic-silicon electronics. We present a general strategy for the efficient assembly of organic molecules on silicon surfaces in both vacuum environment and solution phases via the robust Si-N or Si-O linkage. This is achieved by the reaction between an amine or alcohol functional group and a chlorinated Si surface. The resulting organic layers are thermally stable. This method is applicable for the assembly of a variety of functional organic molecules.

11:30 AM DD4.4
SELF-ASSEMBLED MONOLAYERS (SAMS) ON GOLD DERIVED FROM BIDENTATE ALKANETHIOLS. Nupur Garg, Young-Seok Shon, Ramon Colorado, Jr., Ramon J. Villazana and T. Randall Lee , Department of Chemistry, University of Houston, Houston, TX.

We are developing new types of self-assembled monolayers (SAMs) on gold from the adsorption of specifically designed bidentate chelating alkanethiols. The chelating SAMs exhibit enhanced stabilities and/or unique structural features when compared to those generated from normal alkanethiols. In addition to the construction of densely packed organic thin films, the chelating approach can be used to construct SAMs having packing structures that contain uniquely low densities of alkyl chains. SAMs having homogeneously mixed multicomponent interfaces can also be constructed using this methodology. Herein, we report chelating strategies for the generation of SAMs from three different types of adsorbates: 1,2-bis(mercaptomethyl)-4, 5-dialkylbenzenes, 2,2-dialkylpropanedithiols, and dithiocarboxylic acids. Characterization of these SAMs by contact angle goniometry, ellipsometry, infrared spectroscopy (FT-IRRAS), and X-ray photoelectron spectroscopy (XPS) will be presented.

11:45 AM DD4.5
INFRARED SPECTROSCOPY CHARACTERIZATION OF CHAIN-MELTING IN BIMOLECULAR CHAIN-ASSEMBLIES SANDWICHED BETWEEN PLANAR INORGANIC NETWORKS: LONG CHAIN SILVER THIOLATES. Atul N. Parikh , Jean-Francois Bardeau, Jaime D. Beers, Basil I. Swanson, Chemical Science & Technology Division, Los Alamos National Laboratory, Los Alamos, NM.

The melting of periodic, 2D chain-molecular assemblies of a layered organic-inorganic solid, silver n-octadecyl) thiolate, is examined using temperature dependent, Fourier-transform infrared spectroscopy during the warm-up from -190C to + 200C. The spectroscopic data confirm the presence of a sharp solid-solid transition at 130C previously assigned to a mesogenic bilayer-micellar transition preceeded by a single gradual transition assignable to a pre-melting phenomenon which signals the onset of hindered rotational/twisting motion about the chain-axis. These results are interpreted in terms of the effects of proximal organic-inorganic interface which constrains the chain melting process by frustrating essential translational degrees of freedom.
 

SESSION DD5: NON-SILICATE HYBRID MATERIALS
Chair: Thomas P. Niesen
Tuesday Afternoon, April 6, 1999
Salon 11/12 (M)

1:30 PM *DD5.1
INORGANIC-ORGANIC COMPOSITES BASED ON FUNCTIONALIZED SAMS. Bruce C. Bunker , Sandia National Laboratories, Albuquerque, NM; Jun Liu, Suresh Baskaran, Glen Fryxell, Xiandong Feng, Lin Song, Peter Rieke, Barbara Tarasevich, Gordon Graff and Allison Campbell, Pacific Northwest National Laboratory, Richland, WA.

An overview is provided of research conducted at Pacific Northwest National Laboratory in use of functionalized self-assembled monolayers (SAMS) and surfactants to produce and enhance the performance of inorganic-organic composites. Topics to be covered include: 1) the use of functionalized SAMS to stimulate the nucleation and growth of ceramic phases in ``biomimetic'' processing schemes, 2) the use or organized surfactants as templates to produce non-silica-based mesoporous materials, and 3) the use of SAMS to tailor the surfaces of mesoporous materials for specific applications including selective binding of heavy metals, radionuclides, and other dissolved species and the development of low dielectric constant films for microelectronic applications.
Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under contract DE-ACO4-94A1185000.

2:00 PM DD5.2
SELECTIVE DEPOSITIONS OF Fe-CONTAINING OXIDE FILMS ON MIXED SELF-ASSEMBLED ORGANIC MONOLAYERS USING MICROCONTACT PRINTING. Hyunjung Shin , Kyongmi Lee, Geunbae Lim, Jong Up Jeon and Y. Eugene Pak, Micro Systems Lab., Samsung Advanced Institute of Technology, Suwon, KOREA; Hyejin Im and Eung Soo Kim, Department of Materials Engineering, Kyonggi University, KOREA.

IIn situ patterning of iron-containing oxide thin layers were fabricated via microcontact printing (CP) and selective deposition. CP is used to pattern two different surface moieties of self-assembled organic monolayers (SAMs) on Au/Cr/Si substrates. An elastomeric stamp (poly(dimethylsiloxane); PDMS) having a sub-micron size patterned relief structure were used to transfer either hexadecanethiol (HDT) SAMs that are to sustain deposition of iron oxide precipitates or hydrophilic SAMs (e.g. dithiothreitol (DTT)). Selective depositions were realized through precipitation of iron oxide phases from aqueous solutions at ambient temperature (<100C). 0.05 M of iron nitrate (Fe(NO₃)₂9H₂O) aqueous solutions containing urea under nitric acid (pH < 2) were prepared for selective depositions. X-ray photoelectron spectroscopic (XPS) results showed that iron oxide precipitates (presumably  - Fe₂O₃) were deposited only onto hydrophilic SAMs, but not onto HDT surfaces. Also, scanning electron microscopy (SEM) revealed that the morphology differences of iron oxide films onto DTT surfaces deposited by the CP and directly from the solutions. Auger electron microscopy and atomic force microscopy were used to characterize definition of micron sized patterns of iron oxide thin films.

2:15 PM DD5.3
SYNTHESIS AND CHARACTERIZATION OF TITANIA AND VANADIA THIN FILMS AT ORGANIC SELF-ASSEMBLED MONOLAYERS. Thomas P. Niesen , Jurand Wolff, Joachim Bill, Fritz Aldinger, Max-Planck-Institut für Metallforschung and Institut für Nichtmetallische Anorganische Materialien, Universitaet Stuttgart, Stuttgart, GERMANY.

Self-assembled monolayers (SAMs) on single-crystal Si wafers have been used as substrates for the deposition of oxide thin films. The organic surface has been shown to be effective for promoting the growth of films from aqueous solutions at low temperatures. Recent new results will be presented, including the deposition and characterization of titania and vanadia films. Titania films have been synthesized by hydrolysis of TiCl₄ in aqueous HCl solutions at 80C on sulfonated SAMs. In presence of H₂O₂, the thermal stability of the solutions is enhanced by complexation of free titanium ions. Therefore, uniform films were achieved at higher pH compared to previous research, combined with higher deposition rate. Vanadium-containing films have been formed by hydrolysis and condensation of H₃VO₄ solutions on Si wafers coated with -NH₂ SAMs, likewise at 80C. The as-deposited films consisted of V₂O₅xH₂O in form of turbostratic layers with intercalated water molecules and could be transformed to crystalline vanadia by annealing in air. As-deposited and annealed films were characterized by a variety of spectroscopic and microscopic techniques, including ellipsometry, rutherford backscattering spectroscopy, atomic force microscopy and transmission electron microscopy, to determine thickness, topography, microstructure and chemical composition of the films. Based on these and previous results, the current understanding of the film formation will be discussed.

2:30 PM DD5.4
DEPOSITION OF TIN (IV) OXIDE CERAMIC FILMS ON ORGANIC SELF-ASSEMBLED MONOLAYERS. Sitthisuntorn Supothina, Mark R. De Guire , Arthur H. Heuer, Case Western Reserve University, Department of Materials Science and Engineering, Cleveland, OH; Thomas P. Niesen, Joachim Bill, Fritz Aldinger, Max-Planck-Institut fuer Metallforschung, Pulvermetallurgisches Laboratorium, Stuttgart, GERMANY.

Nanocrystalline thin films of tin (IV) oxide (cassiterite) have been deposited from aqueous solutions of tin (IV) chloride and hydrochloric acid at 80 degrees Celsius. Substrates were 100 silicon wafers, with and without silanol-anchored organic self-assembled monolayers (SAMs). Both static and flowing solutions have been used. The thickness of the films from static solutions is limited to about 50 nm, whereas films with thicknesses of several hundreds of nm have been grown from flowing solutions. The films are pore- and crack-free, adherent and microstructurally uniform on both SAM-covered and bare (oxidized, hydrolyzed) silicon wafers. The role of the substrate in the deposition process will be discussed, as well as that of the flow rate and configuration of the deposition chamber. Characterization of the films using transmission electron microscopy, Rutherford backscattering spectroscopy, atomic force microscopy, and x-ray photoelectron spectroscopy will be discussed.

3:15 PM *DD5.5
ADDITIVE FABRICATION OF MATERIAL MICROSTRUCTURES USING ORGANIC THIN FILM TEMPLATES. Ralph G. Nuzzo , David Payne, Martin Erhardt, University of Illinois at Urbana-Champaign, Department of Chemistry, Urbana, IL.

Additive fabrication involves the directed construction of thin-film microstructures. In this talk I will describe the construction of a variety of thin film microstructures and devices, including waveguides, MOSFET and TFT transistors, ferroelectric capacitors, and metal-silicide Schottky diodes, using non-photolithographic patterning methods. Of particular interest in this work is the combined use of selective deposition chemistries with soft-lithographic patterning methods to facilitate the construction of complex multilayer structures. The current status of progress in these areas will be described.

3:45 PM DD5.6
SYNTHESIS OF TRANSITION-METAL-OXIDE MESO-STRUCTURE THIN FILMS (II). H.S. Zhou , I. Honma, Energy Division, Electrotechnical Laboratory (ETL), AIST, Tsukuba, JAPAN.

Self-assembly organic-inorganic molecules into highly order mesostructured architecture have attracted increasing attention because these materials provide a rich source for scientific researches and technological applications. However, for electronic and optical application, it is very important to control the material's morphology from powder to thin film. We already reported the synthesis of oriented V₂O₅, Fe₂O₃, Nb₂O₅ and TiO₂ transition-metal-oxide meso-structure films with surfactants by a spin coating method. Here we present that the morphologies' transformation of V₂O₅ and TiO₂ transition-metal-oxide meso-structure films. We used the precursor of vanadium tri-n-propoxide oxide, 1-propanol and the surfactant of hexadecyltrimethylammonium bromide (C16TMA) to synthesized V₂O₅ meso-structure film, and used the titanium tetra-iso-propoxide (TTIP), 2-propanol and the surfactant of monododecylphosphate (MDP) for TiO₂ meso-structure film. X-ray diffraction patterns show that both the films oriented in lamellar structures at the first stage. But, it can transfers, according to the aging time at room tempera- ture, from a lamellar or double lamellar phase to a mixture of lamellar and cubic or other mixture phases. The lamellar structures of TiO₂ meso-structure films are collapsed by decomposition of surfactants on about 300C heat treatment for 2 hours. We also investigated the differential thermal analysis (DTA), thermogravimetry (TG) and IR spectra of TiO₂ meso-structure films.

4:00 PM DD5.7
THE SYNTHESIS OF ORGANIC VANADIUM OXIDE LAYERED STRUCTURES. M. Stanley Whittingham , Peter Zavalij, Katana Ngala and Arthur Dobley, Materials Research Center and Chemistry Department, State University of New York at Binghamton, NY.

The formation of organic-inorganic hybrid materials by hydrothermal synthesis has been explored systematically in the case of vanadium oxides. The organic ion or chelating molecule has a profound effect on the structure formed, as also does the pH of the reaction medium and the nature of the reaction medium itself. Recent experiments using the small spherical and very stable tetramethylammonium ion, the hydrogen bonding methylammonium ion, the triethylammonium ion as well as long surfactant ions will be described. A range of structures were formed in these experiments, ranging from one-dimensional inorganic strings, through inorganic layers and tunnel compounds to three-dimensional lattices. These have been characterized and the beginnings of a rational approach to synthesizing such compounds is being seen. This work is being supported by the National Science Foundation, Division of Materials Research.

4:15 PM DD5.8
SOLVOTHERMAL SYNTHESES AND CHARACTERIZATIONS OF ONE-DIMENSIONAL AND TWO-DIMENSIONAL ORGANO-TEMPLATED VANADIUM ARSENATE AND PHOSPHATE PHASES. Yu-Min Tsai, Li-Hsun Hung, Sue-Lein Wang , Dept of Chemistry, National Tsing Hua University, Hsinchu, TAIWAN.

Solvothermal reactions of the piperazine/V/X/O (X = As, P) systems were investigated. Variations in temperature, solvents, stoichiometries of reactants, and starting pH values of the reaction solutions resulted in the isolation of four novel phases: (C₄N₂H₁₂)₂(V₂O₃)₂(AsO₄)(HAsO₄)(H₂AsO₄).4H₂O (1), (C₄N₂H₁₂)(VO)₂(HAsO₄)₃.H₂O (2), (C₄N₂H₁₂)[VO(C₂O₄)(HAsO₄)] (3), and (C₄N₂H₁₂)[V₂O₃(HPO₄)(PO₄)] (4), respectively. Phases 1, 2 and 3 are vanadyl(IV) compounds. They adopt different 1D chain structures. The chains in 1 and 2 contain a common building unit, edge-sharing V₂O₁₀ bioctahedra which are linked by arsenate tetrahedra in different manners. In the structure of 3, chains are constituted by four-connected (-V-O-P-O)₂ units which can be thought as derived from the well-known structure of the VOPO₄.2H₂O. Each of the V centers are as well coordinated by one oxalate group which is acting as a bidentate ligand. It is the first vanadium oxalatoarsenate compound ever reported in the literature. Phase 4 is a mixed-valence vanadyl(IV,V) compound. It adopts a layer structure in which two kinds of V-O polyhedra with different valence on V centers coexist. Each layer is formed of two types of infinite chains interlinked by PO₄ tetrahedra- one contains corrner-sharing V^VO₅ square pyramids and the other contains isolated V^IVO₆ octahedra in four-connected units similar to that in 3. The unified synthetic strategy, crystal structures, structrual relationship, thermal analyses, and magnetic properties of these new phases will be presented in detail.

4:30 PM DD5.9
A NEW ROUTE TO PREPARE HARD AND ANTI-SCRATCHING COATINGS AT ROOM TEMPERATURE. Yanjing Liu, NanoSonic, Richard O. Claus , Dept of Electric and Computer Engineering, Dept of Material Science and Engineering, Virginia Tech, VA; Aprillya Rosidian, Dept of Material Science Engineering, Virginia Tech, VA; Tingying Zeng, Dept of Electrical Engineering, Virginia Tech, VA.

A new method for the preparation of hard and anti-scratching coatings at room temperature has been developed, based on the layer-by-Layer electrostatic self-assembly (ESAM) technique. Highly homogeneous and several micron thick coatings of nanoparticles including ZrO₂, Al₂O₃, SiO₂, and ZrO₂/ Al₂O₃ have been prepared on plastics, glass and other curved substrates. UV-vis spectroscopy, ellipsometry, atomic force microscopy, and nanoindentation tester have been used to characterize the homogeneity, thickness, morphology, and mechanical properties before and after sintering.

4:45 PM DD5.10
REAL-TIME ANALYSIS OF CRYSTALLIZATION AT SURFACES USING LUMINESCENCE MICROSPECTROSCOPY. Michael J. Lochhead , Univ of New Hampshire, Dept of Chemical Engineering, Durham, NH; Lara Touryan, Viola Vogel, Univ of Washington, Dept of Bioengineering, Seattle, WA.

Organic templating of inorganic nano- and microstructures is a promising new approach to advanced hybrid materials. Continued development, however, will rely on an improved understanding of structure-property-processing relations, which in turn will rely on improved methods for characterizing nucleation and growth events in real time. In the current work we use a technique called luminescence microspectroscopy (LMS) that combines the spatial resolution of optical microscopy with the structural sensitivity of rare earth ion spectroscopy. Using europium(III) as a luminescent probe, the technique allows real-time analysis of the evolving crystals while they are in contact with their aqueous growth solutions. Optical imaging provides morphology assessment at micrometer scales while luminescence spectroscopy provides probe ion local bonding information at molecular scales. In the current work, we use LMS to characterize the morphology and phase of biominerals such as calcium oxalate during the early stages of crystal formation. Spatially resolved luminescence spectra are obtained for micrometer-scale crystallites. Beyond the micrometer scale, LMS holds promise for providing spatially resolved spectra from templated crystals and structures smaller than the limits of optical resolution. Technical challenges associated with in-situ nanocrystal characterization will be addressed.

SESSION DD6: MESO-, MICRO-, AND MACROPOROUS HYBRIDS
Chair: Roger A. Assink
Wednesday Morning, April 7, 1999
Salon 11/12 (M)

8:30 AM *DD6.1
TEMPLATED SYNTHESES OF POROUS METAL OXIDES AND HYBRID MATERIALS. Brian Holland, Christopher Blanford, Myong Hoon Lim, Andreas Stein , University of Minnesota, Department of Chemistry, Minneapolis, MN.

Routes of templating inorganic and hybrid solids with periodic pore structures covering a wide range of pore sizes will be discussed. The syntheses are based on molecular and supramolecular templates for the nanometer range, and macromolecular templates for the submicrometer range. Supramolecular templating with surfactant aggregates includes direct syntheses of mesoporous sieves with covalently attached organic surface groups and hydrothermal syntheses of mesoporous sieves with trapped functional organic molecules, such as porphyrins. Macromolecular templating with polystyrene spheres as templates has led to highly periodic macroporous oxides of Si, Ti, Zr, Al, W, Fe, Sb, and a Zr/Y mixture, as well has aluminophosphates and hybrid compositions. These products were synthesized from readily available alkoxide precursors and consisted of periodic, interconnected networks of polycrystalline or amorphous wall with monodisperse submicron pores. Depending on the technique of template removal, the crystallographic phase of the walls could be controlled for some compositions. In the case of silicates, products with bimodal distributions of meso- and macropores were obtained. It is expected that the syntheses can be adapted to many other metal oxides, phosphates, or chalcogenides. As a result, one can forsee an impact on diverse applications that would benefit from the porosity, low density, and order of these novel ceramic structures, such as quantum optics, chromatographic stationary supports, large molecule catalysts, host materials for biological molecules, porous electrodes, metal-ceramic composites, or thermal insulators.

9:00 AM DD6.2
HIERARCHICALLY ORDERED POROUS OXIDES. Peidong Yang , Dongyuan Zhao, Bradley F. Chmelka, Galen D. Stucky, Department of Chemistry, Chemical Engineering, University of California, Santa Barbara, CA; Tao Deng, George M. Whitesides, Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA.

A continuing challenge for materials chemists is the ability to create multifunctional composite structures with well-defined superimposed structural order from nanometer to micrometer length scales. Porous silica, niobia, and titania materials with three-dimensional structures ordered over multiple length scales were prepared by combining micromolding, polystyrene sphere templating and cooperative self-assembly of inorganic sol-gel species with amphiphilic triblock copolymers. The resulting materials show hierarchical ordering over several discrete and tunable length scales ranging from 10 nm to several micrometers. The respective ordering structures can be independently modified by choosing different mold patterns, latex spheres and block copolymers. The examples presented demonstrate the compositional and structural diversities that are possible with this simple approach.

9:15 AM DD6.3
INFLUENCE OF THE PREPARATION CONDITIONS ON THE STRUCTURE OF ORGANICALLY-MODIFIED POROUS SILICATES. Valérie Goletto, Sophie Besson, Valérie Dagry, Florence Babonneau , Chimie de la Matiëre Condensée, UPMC-CNRS, Paris, FRANCE.

The discovery of the MCM series of mesoporous materials has opened up the way to entirely new mesostructured materials, with large surface areas and uniform distribution of pores. Many applications such as adsorption, ion exchange, catalysis and sensing, require the materials to have specific surface properties. One way to introduce oragnic functions at the silica surface is a one-pot synthetic approach, as described in this paper. Organically-modified porous silicates have been prepared from various trialkoxysilanes, RSi(OR')₃ and tetraethoxysilane as hybrid precursors, and cetyltrimethylammonium bromide (CTAB) as structuring agent. Structure of the final samples have been characterized by X-ray diffraction and porosity measurements, as well as ²⁹Si and ¹³C MAS-NMR experiments. The nature of the organic group plays an important role on the extent of mesoscopic order, and different behaviors are observed depending on whether basic or acidic conditions are used.

10:00 AM DD6.4
HYBRID MESOPOROUS MATERIALS AS HOSTS FOR POLYMER COMPOSITES. Karin Moller , Thomas Bein, Department of Chemistry, Purdue University, West Lafayette, IN; Reinhard X. Fischer, Department of Geosciences, University of Bremen,  Bremen, GERMANY.

Hybrid mesoporous materials based on MCM-41 and SBA-type periodic mesoporous hosts are synthesized at room temperature by co-condensation of 3(trimethoxysilyl)propyl methacrylate (TMSiPMA) and tetramethylorthosilicate (TMOS) in the presence of cetyltrimethylammonium chloride or poly(ethylene oxide)- poly(propylene oxide)- poly(ethylene oxide) triblock copolymers. Highly ordered mesoporous materials are obtained after template removal through solvent extraction as shown by x-ray diffraction and transmission electron microscopy. Alternatively, grafting of TMSiPMA and 3-(glycidoxy)propyl trimethoxysilane is performed in a post synthesis step to introduce functionality into the mesoporous hosts. The reactivity of the grafted methacrylate carbon-carbon double bonds is demonstrated by their complete consumption during bromination. The presence of the functional groups within the mesoporous channels is exploited for the formation of inorganic/organic composites on the molecular level: the intra-pore grafted methacrylate groups are polymerized with adsorbed methyl methacrylate monomer (MMA) to form occluded PMMA filaments.

10:15 AM DD6.5
NON-IONIC SURFACTANT AND BLOCK COPOLYMER TEMPLATED MESOPOROUS SILICA FILMS THROUGH EVAPORATION-INDUCED SELF-ASSEMBLY. Hongyou Fan , Yunfeng Lu, Frank van Swol, C. Jeffrey Brinker, Sandia National Laboratories, and the University of New Mexico/NSF Center for Micro-Engineered Materials, The Advanced Materials Laboratory, Albuquerque, NM.

Transparent, defect-free films with controlled pore structure and surface chemistry are of interest for applications such as membranes, sensors, optical hosts, and low K dielectrics. We reported a rapid surfactant-templated approach to prepare a family of mesophase silica films with pore size less than 2 nm. Starting with an oligomeric silica sol plus CTAB, we exploited surfactant enrichment during dip-coating to obtain a family of films exhibiting hexagonal, cubic, or lamellar mesostructures. In this presentation, nonionic/amphiphilic block copolymers have been used to produce mesoporous films. A potential advantage of these nonionic polymer templates is the formation of thicker silica walls resulting in greater thermal and mechanical stability, as well as avoidance of mobile ions that would degrade dielectric performance. In addition, block copolymers template much larger pore size. For example, using Pluronic triblock copolymer (PEO)₂₀(PPO)₇₀(PEO)₂₀, we produced mesoporous thin film with cubic phase. The pore size, porosity, and surface area of the film are 7 nm, 50%, and 910 m²/g respectively. SAXS, TEM, and surface acoustic wave(SAW) sorption techniques are used to characterize the microstructures of the films. Hybrid organic/inorganic mesoporous films are also prepared by co-condensation of TEOS + RSi(OR)₃, where R is a hydrophobic non-hydrolyzable ligand

10:30 AM DD6.6
THERMAL STABILITY OF STRUCTURALLY CONTROLLED LAMELLAE, CUBIC AND HEXAGONAL MESOPOROUS SILICATE THIN FILMS. Itaru Honma , *D. Kundu and H.S. Zhou, Energy Division, Electrotechnical Laboratory, AIST, Umezono, Tsukuba, Ibaraki, JAPAN; *Central Glass and Ceramic Research Institute, Calcutta, INDIA.

Mesostructured silica-surfactant composites in the thin film form are synthesized using cationic surfactant and tetraethyl orthosilicate (TEOS) derived sols via a novel co-assembly process on inorganic surfaces or air/water interfaces with lamellae or hexagonal structure through changing the silica to surfactant ratio. Porous silica films having ordered structure which may find applications in the field of sensors, catalyst etc were formed via the removal of surfactant by thermal treatment. Thermal stability of the composite films of ordered structure is supposed to be an important factor from the view point of application. In this paper, we report here about a simple process to synthesize among lamellae, cubic and one-dimensional hexagonal (1-dH) silica-surfactant composite films on ordinary slide glass by spin coating process. The process provides a systematic changes of the mesophase of lamellae, cubic and hexagonal by surfactant compositions. Thermal decomposition of the surfactant from the composite films has been studied; The surfactant in the mesopore was seen to remove gradually from the composite films in the temperature range 100C - 200C and finally decomposed at 250C. The removal of surfactant destroyed the highly ordered lamellae structure, however, cubic and one-dimensional hexagonal (1-dH) films keep its structure after the calcination of the pores. Thus, highly homogeneous films having cubic and hexagonal pore structure can be generated via the decomposition of surfactant.

10:45 AM DD6.7
SILICEOUS MESOSTRUCTURED CELLULAR FOAMS SYNTHESIZED BY A MICROEMULSION TEMPLATING ROUTE. Patrick Schmidt-Winkel , Wayne W. Lukens Jr., Dongyuan Zhao, Peidong Yang, David J. Pine, Bradley F. Chmelka, Galen D. Stucky, UCSB, Dept of Chemistry, Materials Research Laboratory, Dept of Chemical Engineering, Santa Barbara, CA.

Porous materials with controllable large pore sizes have potential applications as hosts for chemical reactions and for separations involving big molecules. Mesoporous materials are attractive in this respect as they cover pore sizes from 20 to 500 . We present siliceous mesostructured cellular foams (mesocellular foams, MCFs) made up of uniformly sized spheres that are synthesized by a microemulsion templating route. The MCFs represent continuous pore systems with narrow pore size distributions and large surface areas up to 900 m²/g. Uniform spherical cells up to 36 nm in diameter are three-dimensionally interconnected through uniform windows measuring 7-18 nm across. Thermodynamically stable oil-in-water microemulsions are prepared by adding an organic co-solvent (oil) to a dilute solution of a non-ionic triblock copolymer surfactant in aqueous acid. The size of the cells can be controlled by changing the amount of added organic co-solvent during the formation of the templating microemulsion. Adding small amounts of fluoride to the reaction mixture enlarges the window size independently of the cell size and improves the structural homogeneity of the MCF materials. In addition, fluoride addition gives rise to the formation of strut-like matrix arrays that resemble aerogels with the benefit of well-defined pore sizes combined with a significantly facilitated synthesis.

11:00 AM DD6.8
A NOVEL METHOD FOR MAKING MACROPOROUS BULK GELS AND THIN FILMS BY EMULSION TEMPLATING. G. Subramanian , Materials Department, University of California Santa Barbara, CA; V.N. Manoharan, Dept. of Chemical Engineering, University of California, Santa Barbara, CA; A. Imhof, Van der Waals-Zeeman Instituut, Universiteit van Amsterdam, Amsterdam, NETHERLANDS; D.J. Pine, Chemical Engineering and Materials Departments, University of California, Santa Barbara, CA.

Ordered macroporous ceramics such as silica and titania have been synthesized by using alkoxide precursors employing either monodisperse emulsion droplets [1] or polystyrene latex particles as templates [2, 3]. The emulsion templating method offers several advantages over the polystyrene latex particles including easy removal of the template and the ability to produce large monoliths. Removal of the latex particle templates by heat treatment invariably results in structurally fragile materials that fracture into small (< 0.5 mm) pieces. In this paper we describe a novel method of making macroporous bulk gels and thin films of silica using emulsion templating. Bulk gels with dimensions greater than 1 cc can be easily produced. The method involves use of a colloidal sol of silica instead of the usual alkoxide precursors to produce gels. Starting with uniform emulsion droplets and a stable colloidal sol of silica spheres (80-100 nm diameter), we were able to produce macroporous bulk gels and thin films in which the silica particles consolidate around the emulsion template on evaporation of water during drying. The emulsion template was then removed by washing with alcohol leaving macropores in the material. Subsequent heat treatment could then be used to densify the sol particles to produce ordered macroporous silica. Monodisperse emulsion droplets of the required size were made by controlled swelling of monodisperse polystyrene latex particles with organic solvents such as decalin. Good control of the pore size and applicability to other colloidal systems such as titania and zirconia make this method attractive for synthesizing macroporous materials.
1. Imhof, A. and D.J. Pine (1997) Nature 389 (6654): 948-951
2. Holland, B.T., C.F. Blanford, et al. (1998) Science 281: 538-540. 3. Wijnhoven, J.E.G.J. and W.L. Vos (1998) Science 281: 802-804.

11:15 AM *DD6.9 APPLICATIONS OF LOW DENSITY AND HIGH SURFACE AREA ORGANIC-INORGANIC HYBRID MATERIALS. Douglas M. Smith , Steven Wallace, Teresa Ramos, Vinay Menon, NanoPore Incorporated, Albuquerque, NM.

The combination of high surface area and high porosity/low density are important material properties for a number of applications. One rapidly growing example is advanced thermal insulation where densities in the range of 50 to 150 kg/m3 are required but high surface areas (>500 m2/g) are also necessary. The high surface area is necessary in order to achieve small pore sizes as to enable reduced gas phase conduction. Organosilicates offer the advantage for that application of both excellent thermal performance and hydrophobicity. At the opposite end of the value spectrum is low dielectric constant materials for semiconductor interconnects. Low density is desired to lower dielectric constant but pores must all be small (<10 nm) and the material must be hydrophobic. The development of hybrid materials for these and other applications will be presented. In addition, further materials development opportunities for these applications will be highlighted.
 
 
 

SESSION DD7: HYBRID ELECTROCHEMISTRY, PHOTOCHEMISTRY, PASSIVATION, AND SENSING
Chair: Martin Mennig
Wednesday Afternoon, April 7, 1999
Salon 11/12 (M)

1:30 PM *DD7.1
MESOPOROUS HETEROJUNCTIONS AND DYE SENSITIZED NANOCRYSTALLINE SOLAR CELLS. Michael Graetzel , Swiss Federal Institute of Technology, Institute of Photonics and Interfaces, Lausanne, SWITZERLAND.

The salient features of mesoporous junctions composed of an n-type nanocrystalline oxide film the porous network of which is filled with an amorphous p-type organic semiconductor will be discussed. Of particular interest is the case of the dye sensitized heterojunction solar cell based on nanocrystalline TiO₂ and the novel organic hole transport material 2,2',7,7'-tetrakis-(N,N'-di-p-methoxyphenylamine)-9,9-spirobifluorene (spiro-OMeTAD). A monolayer of charge transfer sensitizer present at the junction is used to harvest sunlight and to inject an electron in the conduction band of the oxide. The dye is regenerated by hole injection in the spiro-OMeTAD. The dynamics of this double injection process at the solid jucntion has been investigated by laser photolysis. Light induced charge separation occurs in the femto to picosecond time domain. By contrast the unwanted recombination of electrons injected in the inorganic oxide film with the holes injected in the organic semiconductor is four to five orders of magnitude slower. Solar cells based on this new type of dye-sensitized organic/inorganic hybride heterojunction have been developed and exhibit a strikingly high photon to current conversion effiency.

2:00 PM DD7.2
PHOTOELECTROCHEMICAL PROPERTIES OF SELF-ASSEMBLED MULTILAYERS OF ORGANIC-INORGANIC THIN FILMS AND THEIR USE FOR CATALYSIS. Feras Abdelrazzaq , Raymond Kwong, Alexandre Dokoutchaev, Venkatesan Krishnan, Mark Thompson, Department of Chemistry, University of Southern California, Los Angeles, CA.

We have previously examined the photocurrent generation in metal bisphosphonate multilayer thin films (Nature 1996, 380, 610-612). In this paper we will describe the synthesis and characterization of metal bisphosphonate and metal dithiolate thin films composed of quinones and viologen, based acceptors layers and porphyrin, hydroquinone, phenylene diamine, and dihydroxynaphthalene as donor layers. Zirconium bisphosphonate multilayers of these novel compounds and other metal dithiolate multilayers (-SRS-M-SRS-, R= porphyrin; M=Cu) were grown on different substrates (e.g. Au, Si, etc.) and were studied by AFM, UV-Vis, Fluorescence Spectrometry, Ellipsometry and Cyclic Voltametry. These photoelectroactive films produced photocurrent with a quantum yield of (1-5%) based on absorbed light. Our method of film growth provides control over both the structure and the composition of multilayer films leading to efficient photoinduced charge separation. These photoelectrode generated photocurrent when irradiated with ultraviolet and visible light. The photoelectrode can then be repeatedly cycled giving the same current with no major degradation. In these experiment we shift the active wave length region of these devices by choosing the appropriate redox species that absorbs in the desired region. Interestingly, we find that incorporating these redox active species in a cascade type arrangement (according to their redox potentials and optical properties) resulted in an increase in the quantum yield and increase of electron transport through the material. When these photoactive multilayers were grown on silica-supported colloidal metal particles (e.g. Pt, Pd) they have been utilized for photochemical hydrogen production from water. The electrochemical and photochemical properties of these films will be discussed.

2:15 PM DD7.3
SYNTHESIS OF SILICA/PEO NANO-HYBRIDS PROTONIC CONDUCTING MEMBRANE THROUGH SOL-GEL PROCESSES. Itaru Honma , Electrotechnical Laboratory, AIST, Tukuba, JAPAN; Y. Takeda, Kougakuinn University, Tokyo, JAPAN and J.M. Bae, NEDO, JAPAN.

In this paper, the synthesis of new protonic conducting organic/inorganic nanocomposites electrolyte membrane is reported and the conductive properties at the elevated temperature with various humidities have been investigated. The electrolyte membrane is composed of nano-level ceramic/polymer composites which is synthesized through sol-gel processes. Silica (SiO₂)/Polyethyleneoxide (PEO) organic/inorganic nanocomposite (SPC) are remarkable family of isotropic, amorphous, nanocomposite materials. The rigid silica domain in the composite results in high strength and temperature toughness while the PEO chain serve to provide flexibility and melt processibility. The SPC doped with acidic surfactant of monododecylphosphate (MDP) at different rate are casted from the mixed solution and the membrane are dried at ambient temperature. The Silver electrode are attached on both sides of the membrane and protonic conductivities are measured at elevating temperatures and various humidities. Protonic conducting properties of SPC doped with MDP in the temperature range from 60C to 160C with humidifier temperature higher than that of the operating cell by 15C for hydrogen and 10C for oxygen lines. The protonic conductivity decreases with elevating temperature from 5 x 10^-3 S/cm at R.T. to approximately 10^-4 S/cm at 160C, which is highly conductive as an organic/inorganic hybrid membrane..

2:30 PM DD7.4
NANOSTRUCTURAL LITHOGRAPHY VIA PHOTO-INITIATED PHASE TRANSFORMATION OF SILICA-SURFACTANT ASSEMBLIES. Dhaval Doshi ¹, Nicola Huesing², Hongyou Fan¹, Alan Hurd³, C. Jeffrey Brinker^1,3, ¹The University of New Mexico/NSF Center for Micro-Engineered Materials, Albuquerque, NM; ²Technische Universitat Vienna, AUSTRIA; ³Sandia National Laboratories, Albuquerque, NM.

Cooperative self-assembly processes of inorganic species and amphiphilic molecules have experienced major advances over the past six years. Various pathways have been explored to access a wide spectrum of mesostructured materials with tunable pore sizes and arrangements and good compositional control. A variety of macro- and microstructures have been synthesized such as powders, fibers, monolith, thin films, hollow and transparent hard spheres and aerosol particles which find applications in catalysis, membrane separation, sensors, optoelectronics, and as novel nanomaterials. However, the ability to design these materials with spatially controlled combinations of different mesophases or compositions, and therefore different properties, would greatly enhance their utility as nanofunctional surfaces. We present a simple lithographic procedure which allows a deliberate control of structure and properties of a meso-ordered silica film through optical mediation. This nanostructural lithography process exploits the pH sensitivity of supra-molecular self-assembly. Through addition of a photoacid or base generator in the coating sol along with surfactant and silica, dip coating results in the self-assembly of continuous, ordered photosensitive films. UV exposure through a mask produces local pH changes, inducing mesostructural phase transitions. Two surfactant systems (CTAB and Brij 56) are studied. X-ray diffraction, transmission and scanning electron microscopy, optical microscopy, ellipsometry, MAS-NMR and atomic force microscopy were used to characterize the patterned nanostructured surfaces. Additionally, lithographically patterned films are also formed by in situ polymerization of organic molecules within the silica-surfactant assembly leading to a true inorganic-organic nanocomposite material.

3:15 PM DD7.5
SOL-GEL SYNTHESIS OF MOLYBDENUM OXIDE/POLY- PYRROLE HYBRIDS. Winny Dong and Bruce Dunn, UCLA, Los Angeles, CA.

An advantage of inorganic/organic materials is that each constituent can contribute to a specific property. The goal of synthesizing molybdenum oxide/polypyrrole hybrid aerogels is to produce a cathode material for rechargeable lithium batteries. Molybdenum oxide provides the lithium intercalation capacity while polypyrrole provides the high electrical conductivity. This material can be made as aerogels to further increase Li capacity through its high surface area. Molybdenum oxide/polypyrrole hybrid aerogels and xerogels have been synthesized through the sol-gel method. Simultaneous polymerization where oxidation of the pyrrole occurs with the reduction of the molybdenum leads to a molecular level composite. This hybrid shows increased conductivity (2E-2 S/cm) over molybdenum oxide gels (5E-4 S/cm). The increased conductivity has been achieved without the use of oxidizing agents. The relationship between synthesis and conductivity will be discussed. An increase in lithium intercalation capacity has also been observed (from 1.1 Li/Mo to 1.6 Li/Mo).

3:30 PM DD7.6
IN SITU INTERCALATION/POLYMERIZATION OF MELANIN INTO VANADIUM PENTOXIDE. H.P. Oliveira , C.L.P.S. Zanta, A.C. Galina, USP, DQ-FFCLRP, Ribeirao Preto, BRAZIL; C.F.O. Graeff, USP, DFM-FFCLRP, Ribeirao Preto, BRAZIL.

The possibility of combining the properties of organic and inorganic compounds in a unique material is an old challenge. These new materials, considered as innovative advanced materials, promise new applications in many fields such as optics, electronics, ionics, mechanics and biology. V₂O₅ xerogel have interesting conducting as well as electrochemical properties like the laminar (or 2D ) structure adequate for intercalation reactions. Melanin is a bio-polymer with interesting properties like the high photo-absorption in a wide range of photo energies as well as good photoconductivity. The films were obtained by inserting 3,4-dihidroxi-fenialanina (DOPA) in a solution with HVO₃, which suffered a oxidative polymerization/intercalation process, forming a gel with a dark blue metallic color. The films were characterized using UV transmission spectroscopy, FTIR, ESR, X-ray diffraction, and cyclic voltammetry as well as spectroelectrochemistry. The X-ray diffractograms indicate that the laminar structure of the V₂O₅ is preserved but the inter-planar space increased from 1.18 nm to 1.38 nm. The FTIR and ESR spectra confirms that the V₂O₅ structure is preserved, however the presence of melanine induces the reduction of V ions to V^IV. The increase in the inter-planar spacing is observed to increase the stability and reproducibility of the electrochemical insertion/de-insertion of Li+. This increase in stability is also observed in the electrochromic properties of the film, which are fully reproducible even after more than 30 oxidation-reduction cycles. The presence of melanin induces the appearance of a new broad absorption band in the reduced state (-0.9V) at around 750 nm attributed to a charge transfer from V(IV) to O, in good agreement with the ESR results.

3:45 PM DD7.7
SYNTHESIS AND CHARACTERIZATION OF PIPERIDINE INTERCALATES OF  AND -HAFNIUM PHOSPHATE. M. Luz Rodrigues, Luisa M. Barcina, Maria A. Villa-Garcia , Ricardo Llavona, Marta Suarez, Julio Rodriquez, Departamento de Quimica Organica e Inorganica, Facultad de Quimica, Universidad de Oviedo, Oviedo, SPAIN.

The Intercalation chemistry of  and  - metal (IV) phosphates is dominated by the presence in the interlayer region of Bronsted acid groups. Species with sites that can be protonated are preferred guests. In the case of the amines, the intercalation reaction is driven by an acid-base interaction between the P-OH groups of the layer and the amino groups. For a given guest the intercalation can lead to the formation of various organic-inorganic hybrid materials, that differ in composition and interlayer distance. This work describes the intercalation reactions of piperidine into  and  -hafnium phosphate.
and  -hafnium phosphate were equibrated during 5 days, with aqueous solutions of piperidine containing from 0.5 to 10 mmol amine/g of phosphate. Piperidine intercalates were also obtained by exposing  -hafnium phosphate to an atmosphere saturated with piperidine vapour.
The organic-inorganic intercalates were characterized by chemical and thermal analysis, X-ray diffraction and IR Spectroscopy.
The results obtained show that the intercalation process of piperidine in  -HfP in aqueous solution takes place with the formation of only one phase of composition Hf(HPO₄)₂ C₅H₁₁N  H₂O and d₀₀₂ = 13.3 . No intermediates phases have been detected and the amine is not able to saturate the material. This result is analogous to that obtained when the intercalation process occurs with piperidine in vapour phase; different results were obtained when the intercalation process takes place in pure amine, where saturation is reached with formation of the Hf(HPO₄)₂ 2C₅H₁₁N  H₂O(d₀₀₂ = 15.4 . In  -HfP the final phase obtained in aqueous solution is the same than that obtained when the process is carried out in pure amine, Hf(PO₄) (H₂PO₄)  C₅H₁₁N  2H₂O (d₀₀₂= 18.0 ) however the process takes place with the formation of an intermediate phase of composition Hf (PO₄) (H₂PO₄)  0.38C₅H₁₁N  2H₂O (d₀₀₂ = 13.9  that was also detected when the intercalation process occurs in vapour phase.
 
 

4:00 PM DD7.8
SYNTHESIS OF NANO-SCALE ZEOLITE FILMS FOR VAPOR-SENSING DEVICES. Svetlana Mintova , Shangyi Mo and Thomas Bein, Department of Chemistry, Purdue University, West Lafayette, IN.

Seed-based synthesis methods for ultra-thin films of different molecular sieves have been developed. The different pore sizes and large specific surface areas of BEA, MFI, LTA and AFI type colloidal molecular sieves synthesized on sensor substrates make them suitable materials for the design of sensors with high selectivity and sensitivity. The dimensions of the colloidal particles are in the range of 40-100 nm, which leads to the formation of ultra-thin films with controlled thickness. Quartz crystal microbalances (QCM) were used as substrates for the deposition of zeolite films with different thickness by varying the adsorption conditions of colloidal zeolite seeds, and the temperature and duration of subsequent hydrothermal treatments. In very thin films, most of the crystalline materials are oriented on the sensor surfaces. Computer-controlled sorption measurements on sensor devices coated with ultra-thin and very stable zeolite films demonstrate high molecular shape selectivity based on the molecular sieving capabilities of the zeolites. The equilibration rates of different vapors are controlled by the nature of the molecular sieve, and by the thickness and texture of the films. Fast response and excellent reversibility were obtained for thin colloidal layers, which show remarkable sensitivity at low vapor concentrations.

4:15 PM DD7.9
CORROSION RESISTANT AND HIGH TEMPERATURE COATINGS FROM PRECERAMIC POLYMERS. Y.D. Blum , S.M. Johnson, D.B. MacQueen and C. Kanazawa, SRI International, Menlo Park, CA.

Corrosion resistant and coatings stable at high temperature can be prepared using low-cost preceramic polymers. Commerically available polyhydridomethylsiloxanes, [MeSiHO]_x are firstly modified by catalytic techniques and then mixed with ceramic and metallic powder fillers to form suitable slurries or ``paints''. Alternatively, the polymers used as clear coats. One-pot, and in-situ polymer modifications above to conveniently control parameters such as surface wetting, curability, hardness, and shelf stability, and hydrophobicity. Several unique polymers have been produced using transition-metal catalyzed dehydrocoupling reaction including polymers containing over 80 mol of the monomeric units [MeSi(OH)(O)].
Thick coatings can be deposited (in the range of 50 to 100m per layer). The coatings are cured at room temperature and remain stable at temperatures above 600C when coated on aluminum or steel. Coatings cured at room temperature already demonstrate excellent corrosion resistance properties. Thick coatings on ceramics maintain their integrity and bonding to the substrates at temperatures as high as 1500C. Formulation strategies and the importance of polymer modifications will be discussed. Characterization of coatings and performance evaluation in corrosive environments will be presented.

4:30 PM DD7.10
HOST-GUEST SYSTEMS IN THE DEVELOPMENT OF ANTICORROSIVE INTERACTIVE POLYMERIC FILMS. Luciana M. Estevao , Regina S. Nascimento, Universidade Federal do Rio de Janeiro, Instituto de Quimica, Rio de Janeiro, BRAZIL.

Techniques have been developed in which volatile corrosion inhibitors (VCI) are incorporated into polymer films in order to reduce the corrosion of metallic objects that occurs due to the condensation of water vapor inside polymeric packaging. These inhibitors are transferred to the metal surface by diffusion through the gas phase and are then either adsorbed directly onto the metal or dissolved in surface moisture films. Hence, the major parameters to be considered when using a VCI are their volatility and, when processed in polymeric films, their thermal stability. However, thermally stable VCIs such as dicyclohexylammonium phosphate and p-nitrobenzoate, have relatively low volatility and may fail to meet VCI standards. The most efficient and widely used VCI, dicyclohexylammonium nitrite (DICHAN) degrades in the film processing temperature and is thus inadequate for this purpose.
The aim of this project was to develop interactive films making use of host-guest systems, where dicyclohexylammonium p-nitrobenzoate and phosphate were adsorbed on NaY zeolite and diatomaceous earth, thus controlling the volatility of the inhibitors. The changes in volatility of the various systems were determined by TG/DTG analysis, and their protective properties, by accelerated corrosion testing, making use of carbon steel test coupons. The most promissing VCI/Inorganic support systems were processed with a LDPE/EVA mixture to produce anticorrosive films, which were thereafter submitted to further corrosion testing.
The VCI systems produced presented good thermal stability and the results showed that the adsorption of the VCIs on the supports shifted the DTG peaks to lower temperatures, indicating an increase in volatility, which in turn led to a greater corrosion protection in phosphate systems. It was thus observed that polyolefin interactive films of dicyclohexylammonium phosphate guest molecules on porous inorganic support hosts gave rise to an efficient means of corrosion protection for ferrous materials.

4:45 PM DD7.11 SYNTHESIS OF HYBRID ORGANIC-INORGANIC SOL-GEL COATINGS FOR CORROSION RESISTANCE. Tammy Metroke , Edward Knobbe, Oklahoma State Univ, Dept of Chemistry and the Environmental Inst, Stillwater, OK; Robert Parkhill, Wright Laboratories, Materials Directorate, Wright Patterson Airforce Base, Dayton, OH.

Sol-gel derived organically-modified silica thin films are being investigated as potential replacement systems for chromate-based conversion coatings for aluminum-skinned aircraft. Hybrid organic-inorganic thin films, which may be tailored to have exceptional durability and adhesion, while also providing a dense, flexible barrier, have been found to offer protection from the permeation of water and corrosion initiating species. Preparation, characterization, and corrosion resistance behavior of sol-gel derived RSi(OCH₃)₃-TEOS thin films are presented.
 
 
 

SESSION DD8: POSTER SESSION:
HYBRID SYNTHESIS
Wednesday Evening, April 7, 1999
8:00 P.M.
Salon 7 (M)

DD8.1
SUPERLATTICES OF SEMICONDUCTOR QUANTUM SIZE PARTICLES IN LAYERED ORGANIC ACIDS. Ronit Popovitz-Biro , Shouwu Guo, Volker Hensel, Leslie Leiserowitz, Meir Lahav, The Weizmann Institute of Science, Department of Materials and Interfaces, Rehovot, ISRAEL.

The preparation and control of size and organization of semiconductor nanoparticles has been a challenge in materials chemistry research over the last years. This goal has been aproached from several directions such as the use of reverse micelles¹ or amphiphilic polymers² as media for their synthesis and arrangement. Previous studies in our laboratory demonstrated that the crystalline lattice of ,-alkanedicarboxylate metal salts can be used as confining templates for the synthesis of nanoparticles, showing a dependance of particles size on chain length³ . Here we report the preparation of lead sulfide and cadmium sulfide quantum particles with a high degree of monodispersity arranged in periodic layers within organic matrices. Superlattices of the particles have been generated in crystals or thin films of long chain amphiphilic acids by topotactic gas-solid reactions of the lead or cadmium salts with H₂S gas. These metal salts pack in layer structures and the metal ions are arranged in 2D layers that are separated from one another by the distance defined by the dimensions of the organic bilayer. X-ray powder diffraction (XRD) and transmission electron microscopy (TEM) reveal that the ordered structure of the reactant crystal or film has been retained in the organic-inorganic composite. The approach is demonstrated by four examples of organic matrices: crystals of alkanoic acids, self-organized thin films of -hydroxyalkyloxy-phenyl-propionic acids spread at the air-solution interface⁴, crystals of alkyloxy-phenyl-propionic acids and crystals of alkoxybenzoic acids.
(1) Motte, L.; Billoudet, F.; Lacaze, E.; Doin, J.; Pileni, M.P., J.Phys.Chem.B 1997, 94, 3104.
(2) Osenar, P.; Braun, P. V., Stupp, S.I., Adv.Mater. 1996, 8, 1022.
(3) Guo, S.; Popovitz-Biro, R.; Weissbuch, I.; Cohen, H.; Hodes, G.; Lahav, M., Adv.Mater. 1998, 10, 121.
(4) Guo, S.; Popovitz-Biro, R.; Arad, T.; Hodes, G.; Leiserowitz, L.; Lahav, M., Adv.Mater. 1998, 10, 657.

DD8.2
PREPARATION OF NOVEL HOLLOW FIBER SILICA USING AN ORGANIC GEL AS A TEMPLATE. Yoshiyuki Ono , JST, Chemotransfiguration Project, Kurume, JAPAN; Junichi Hojo, Kyusyu Univ, Dept of chemistry and Biochemistry, Graduate School of Engineering, Fukuoka, JAPAN; Seiji Shinkai, JST,Chemotransfiguration Project, Kurume, JAPAN.

A novel hollow fiber silica was produced by the use of the fibrous structures of an organic gel. The inner diameter ranged from 10 to 200 nm and the outer diameter ranged from 50 to 300 nm. An organic gelator was dissolved in dichloromethane and mixed with the silicate solution which consisted of TEOS/water/catalyst and the solvent that could be gelated by the organic gelator: for example, TEOS/water/acetic acid and TEOS/water/benzylamine/1-butanol. Subsequently, the resultant solution was evaporated in vacuo until the dichloromethane was removed to give a turbid gel. The SEM images of the product showed well grown fibrous structures. After calcination, it was clearly seen by TEM images that these fibers have a tubular structure. The preferable gelator to form hollow fiber silica is one which has cationic charges: for example, a quaternary ammonium halide salt or a crown ether including a metal cation. Cholesterol derivatives having azobenzene were used as the organic gelator in this study. The diameter of hollow was comparable with that of the organic gelator fibrils, so the gelator acted as a template. Since the propagation species of silicate in the solution of acetic acid or benzylamine are considered to be anionic, the electrostatic interactions may be important for adsorption of silica onto the template fibers.

DD8.3
SELECTIVE METAL DEPOSITION VIA OMCVD ONTO SAMS. Roland A. Fischer , Carl C. Winter, Ulrike M. Weckenmann, Ruhr-Universität Bochum, Anorganische Chemie II, Bochum, GERMANY.

We demonstrate the selective deposition of ultrathin gold layers by organometallic chemical vapor deposition (OMCVD) onto SH-terminated self-assembled monolayers (SAMs) using the volatile gold precursor Me₃PAuMe. OMCVD has proven to be an ideal method for the deposition of metals on SAMs which are extremely sensitive to elevated temperatures. Given a suitable surface functionality the deposition can be carried out under very mild conditions at high rates. The selectivity of this method relies on different rates of the surface reaction on different surfaces. We have deposited gold on patterned SAMs generated by microcontact printing with regions terminated by CH₃ or SH. This resulted in the formation of a microstructured gold layer since deposition only occured on the reactive SH-terminated areas. The deposition of gold and the formation of Au-S-bonds on the surface has been shown by XPS (changes in the Au4f and S2p peak intesities). AFM images reveal that the gold deposited on the surface of the SAM forms clusters (20-40 nm) rather than a film of uniform thickness. Further methods of investigation include RAIRS, SD-MS and STM.

DD8.4
POLYSILSESQUIOXANES DERIVED FROM METHACRYLOXYLPROPYLTRIMETHOXYSILANE: COPOLYMERIZATION REACTION WITH STYRENE. Patricia Eisenberg , Juan Carlos Lucas, INDEMAT-UNSAM-CITIP-Inst. Nac. de Tecnologia Industrial, Bs. As., ARGENTINA; Roberto J. J. Williams, INTEMA-CONICET, Univ. Nacional de Mar del Plata, Bs. As., ARGENTINA.

Polysilsesquioxanes (SSQO) are the reaction products of the hydrolytic condensation of trifunctional organosilicon monomers (RSiX₃). The term polysilsesquioxane is used to describe both oligomeric polyhedra that are fully condensed structures ([RSiO_1.5]_n, with n = even integer number), and open structures that are incompletely condensed reaction products ([RSiO_1.5-x(OH)_2x-n]_n) (1). If R is a polymerizable functional group, a polymer network derived from the SSQO may be obtained. In this presentation we discuss the synthesis and characterization of the particular hybrid material derived from the hydrolytic condensation of methacryloxypropyl trimethoxysilane, followed by copolymerization with styrene.The hydrolytic condensation was performed in bulk, using formic acid 98-100 (2), at 50C, 2 days. The distribution of reaction products was followed by SEC. After an initial period of several hours, two main peaks were observed. The first one was assigned to SSQO with n = 8-12 while the second one was ascribed to SSQO with n = 16 .The organic polymer network was obtained by a free-radical copolymerization of R groups with styrene (10-90  wt). The copolymerization reaction was followed by DSC. For formulations containing 60 wt of styrene or more, the reaction heat was constant and equal to the one reported for the styrene homopolymerization .Formulations containing lower styrene contents exhibited a decrease in the overall reaction heat. Thermal and mechanical properties of the hybrid materials were determined as a function of the styrene content. The Tg was determined by TMA. Tg was equal to 100C for pure polystyrene and increased to about 140C for the formulation with 60 wt styrene. Samples with lower styrene contents did not exhibit a Tg by TMA up to 300C. Thermal gravimetric analysis showed that the decomposition temperature increased from 418C (80 wt styrene) to 431C (10 wt styrene). The ceramic yield to SiO₂ (oxygen at 900C) (3) was the theoretical one within experimental error. A significant increase in Barcol hardness was observed (72 for 10 wt styrene; 44 for 80 wt styrene). Ref. :
1. Provatas, A.; Matisons, J.G.; Trip, 5, 327, 1997.
2. Sharp, K.; J.Sol.-Gel Sci. Techn.; 2, 35, 1994. 3. Sellinger,A.; Laine,R.M.; Macromolecules,29, 2327, 1996.

DD8.5
PREPARATION OF SPHERICAL HYDROUS SILICA OXIDE PARTICLE UNDER ACIDIC CONDITION VIA SOL-GEL PROCESSING. Yang Wu , Satsuki Kitajima, Mika Ohsawa, Mamoru Aizawa, Kansai Research Institute (KRI), Kyoto, JAPAN.

It is well known to prepare spehrical particles via sol-gel processing employing such famous process as Stoeber Process, and so on. Usually, particles are formed under basic condition, however, we have found that spherical hydorus oxide particles could be formed under acidic condition. The reaction mechanism was supposed to be a kind of suspension polymerization. Those particle diameter ranged from 1 micrometer to 1000micrometer. Particle's size was controlled by adding seed particles, other metal species like Ti, Zr and so on. During the particle formation process, we could easily introduce not only functional molecules but also fine particles into spherical particles. Those particles were basically optically clear and showed some interesting properties.

DD8.6
A SILICON AND DEUTERIUM NMR INVESTIGATION OF MOLECULAR TEMPLATING IN AMORPHOUS SILICAS. Roger A. Assink ¹, Carol A. Click², Todd M. Alam¹, C. Jeffrey Brinker^1,3 and Sujit J. Naik³, ¹Sandia National Laboratories, Albuquerque, NM; ²University of Missouri, Rolla, MO and ³University of New Mexico, Albuquerque, NM.

The precise pore sizes defined by crystalline zeolite lattices have led to intensive research on zeolite membranes. Unfortunately zeolites have proven to be extremely difficult to prepare in a defect-free thin film form needed for membrane flux and selectivity. We introduce tetrapropylammonium TPA (a structure directing agent for zeolite ZSM-5) into a silica sol and exploit the development of high solvation stresses to create templated amorphous silicas with pore apertures comparable in size to those of ZSM-5. Silicon and deuterium NMR experiments were performed to evaluate the efficacy of our templating approach. The 29Si NMR spectrum of the silica matrix was observed by an intermolecular cross-polarization experiment involving the 1H nuclei of TPA and the 29Si nuclei in the silica matrix. The efficiency of the cross-polarization interaction was used to investigate the degree to which the matrix formed a tight cage surrounding the template molecule. Normally prepared xerogel materials exhibited only weak interactions between the two sets of nuclei. Drying under reduced pressure where solvation stresses are maximized resulted in significantly increased interactions. Analogous materials were prepared using fully deuterated TPA. The 2H NMR wideline spectra consisted of a partially narrowed resonance, corresponding to template molecules which were undergoing restricted rotational motion, and an isotropically narrowed resonance, corresponding to molecules which were undergoing rapid rotational motion. The number of freely rotating template molecules decreased for specimens dried under reduced pressure, consistent with improved templating of amorphous silica by TPA.
Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under Contract DE-AC04-94AL85000.

DD8.7
THERMOSETTING MACHANISM STUDY OF ORGANOSILICON POLYMER CONTAINING CARBORANE BY SOLID-STATE NMR SPECTROSCOPY. Hideaki Kimura , Kouichi Okita, Japan Chemical Innovation Institute, Advanced Polymer Lab, Tsukuba, JAPAN; Motokuni Ichitani, Mitsuharu Yonezawa, Toshiya Sugimoto, Sekisui Chemical Ltd, Advanced Polymer Lab, Osaka, JAPAN.

The thermosetting mechanism of organosilicon polymer containing carborane has been studied utilizing the ¹³C and ²⁹Si solid-state NMR method. The polymer having C-C triple bond in the main chain and CH=CH₂, Si-H bonds, and carborane in the bulky side chain, shows a very highly thermal stability by curing at 350C. From these results, it was found that the CH=CH₂, Si-H bonds in the side chain completely vanished up to 250C, whereas all of C-C triple bonds in the main chain were not involed in cross-linking reaction even at 350C. Consequently, it is thought that the organosilicon polymer was flexible even after cross-linking.

DD8.8
ULTRATHIN FILMS OF DENDRIMER-METAL NANOCOMPOSITES. Lajos Balogh , University of Michigan Center For Biologic Nanotechnology, Ann Arbor, MI; Srinivas Uppuluri, Jing Li and Donald A. Tomalia, Michigan Molecular Institute, Midland, MI; Gary. L. Hagnauer, AMSRL-WM-MA, US Army Research Laboratory, APG, MD.

Dendrimer based nanocomposites (DNCs) are recently discovered hybrid materials displaying unique physical and chemical properties as a consequence of the atomic/molecular level dispersion of inorganic guest domains within a dendritic organic host. Self-assembled monolayers (SAMs) of molecules are capable of molecular recognition and have many potential applications. Layer-by-layer electrostatic deposition is a facile way of creating orderly deposited multilayer films. In this work poly(amido-amine) dendrimers were used to prepare multilayers of zero valent metals on different substrates by using Cu(0)-PAMAM, Ag(0)-PAMAM and Au(0)-PAMAM dendrimer nanocomposites. Gold and silver containing intradendrimer and interdendrimer multilayer alloys of Ag(0)-PAMAM, Au(0)-PAMAM and (Au(0)-Ag(0))-PAMAM nanocomposites were also fabricated. By employing DNCs, not only the fabrication of multilayers proved to be quick and efficient but the composition and structure of multilayers can be varied at will. Advantages of using dendrimer nanocomposites will be discussed in the light of dynamics of multilayer formation. Also, uncommon, architecture-dependent properties of the metal multilayers will be compared.

DD8.9
DIALKYLENECARBONATE-BRIDGED POLYSILSESQUIOXANES HYBRID ORGANIC SOL-GELS WITH A THERMALLY LABILE BRIDGING GROUP. Douglas A. Loy , James V. Beach, Brigitta M. Baugher, Roger A. Assink, Encapsulation and Foams Department, Sandia National Laboratories, Albuquerque, NM; Kenneth J. Shea, Joseph Tran, Department of Chemistry, University of California, Irvine, CA; James H. Small, Polymers and Coatings Group, Los Alamos National Laboratory, Los Alamos, NM.

Gelation of polysilsesquioxanes is limited to those functionalized with a relatively limited group of organic substituents. By capitalizing on the greater propensity of bridged polysilsesquioxanes to form gels, it is possible build polymeric architectures whose bridging organic functionality contain a masked chemical functionality that can be thermally released after the desired gel structure has been obtained. Dialkyl carbonates can serve as masking groups for either an olefin and an alcohol or two alcohols depending on how the carbonate is decarboxylated. In this work we prepared dialkylenecarbonate-bridged polysilsesquioxane gels by the sol-gel polymerization of bis(triethoxysilylpropyl)carbonate (1) and bis(triethoxy- silylisobutyl)carbonate (2). Thermal treatment of the resulting non-porous xerogels and aerogels at 300 °C resulted in the quantitative decarboxylation of the dialkylenecarbonate bridging groups to give new hydroxyalkyl and olefinic substituted polysilsesquioxane monolithic xerogels and aerogels that can not be directly prepared through direct sol-gel polymerization of alkoxysilane precursors.

DD8.10
METAL PHOSPHONATE LANGMUIR-BLODGETT FILMS CONTAINING FUNCTIONAL ORGANIC GROUPS. Melissa A. Petruska and Daniel R. Talham, Univ of Florida, Dept of Chemistry, Gainesville, FL.

The Langmuir-Blodgett (LB) deposition procedure allows for the fabrication of thin films by arranging amphiphilic molecules at an air-water interface before transferring them onto a solid support. By modeling LB films after organic/inorganic layered solids, the lattice energy and other physical phenomena associated with inorganic extended solids can be incorporated into the thin films. For example, octadecylphosphonic acid films as divalent, trivalent, or tetravalent metal salts form bilayer LB film structures where the metal phosphonate networks have the same in-plane binding as the analogous layered solid-state metal alkylphosphonates. This metal/phosphonate network also provides the opportunity to incorporate functionalized organic groups into the LB films, thereby creating a material where both the inorganic and the organic components add function to the LB assembly. Working toward such systems, we have recently introduced larger organic moieties into LB films formed by the metal phosphonate approach. Studies of an azobenzene-derivatized phosphonic acid have probed the limitations encountered when forming these metal phosphonate films, particularly when the preferred organic packing is incommensurate with the inorganic lattice. Phosphonic acids containing tetrathiafulvalene groups have also been synthesized, and metal phosphonate films of these derivatives with divalent and trivalent metal ions have been prepared and characterized using FTIR, optical spectroscopy, and conductivity measurements.

DD8.11
FORMATION AND HYDROLYTIC STABILITY OF OXYGEN BRIDGED HETEROMETAL BONDS (Si-O-Ti, Si-O-Zr, Si-O-Ta) IN SOL-GEL MATERIALS. Manfred Nacken , Dagobert Hoebbel, Helmut Schmidt, Institut fuer Neue Materialien, Saarbruecken, GERMANY.

Glycidoxypropyltrimethoxysilane (GPTS) and metal alkoxides are frequently used in preparation of heterometal hybrid polymers, which find application in electronic and optical industry e.g. as hard coatings of organic polymers and contact lens materials. Such materials require a high homogeneity of the structural unit on molecular level, which is supported by the formation of oxygen bridged heterometal bonds and their hydrolytic stability. By means of ²⁹Si and ¹⁷O NMR the formation of heterometal bonds like Si-O-Ti, Si-O-Zr, Si-O-Ta could be identified in the GPTS-hydrolysates with Ti(OEt)₄, Ti(OEt)₃AcAc, Zr(OBuⁿ)₄, Zr(OBuⁿ)₃AcAc, Ta(OEt)₅ or Ta(OEt)₄AcAc (AcAc = acetylacetone ligand). Signals of heterometal bonds can be detected in ¹⁷O NMR spectra in the region of 170 to 350 ppm. They are characterised in ²⁹Si NMR spectra by defined chemical shifts to low (Si-O-Ta) and high magnetic fields (Si-O-Ti, Si-O-Zr). The use of complexed metal alkoxides with AcAc as ligands leads to well resolved ²⁹Si NMR spectra, which make the distinction between homo- and heterocondensed species easier. The addition of water (0.5-2 H₂O/alkoxy group) to heterometal bond containing systems leads to a degradation of Si-O-M bonds (M= Ti, Zr, Ta) in favour of more homocondensed species, which can lower the homogeneity of such hybrid materials on a molecular level.

DD8.12
ATOMIC FORCE MICROSCOPY STUDY OF THE REORGANIZATION OF LANGMUIR-BLODGETT FILMS. Dawn Y. Takamoto , Evgeny Ter-Ovanesyan and Joseph A. Zasadzinski, University of California, Santa Barbara, Dept of Chemical Engineering, Santa Barbara, CA.

The practical applications of Langmuir-Blodgett (LB) monolayers and multilayers are limited by a spontaneous reorganization in aqueous solution. The reorganization of cadmium fatty acid salt LB films was studied by equilibrating under aqueous subphase for various times, and then imaging with the atomic force microscope (AFM) in air. We have found that constant thickness films deposited on both hydrophilic and hydrophobic substrates (mica and silicon) are unstable to bilayer step defects.
Multilayer fatty acid salt LB films are isostructural with centrosymmetric bulk soap crystals. The LB technique deposits asymmetric molecules onto the substrate surface which are inherently unstable, and the molecules undergo a conformational transition resulting in defective layers. To elucidate the mechanism for the reorganization, we deposited LB films with layers of varying chain lengths. From measurements of the heights of the bilayer step islands and holes formed, we were able to determine how the molecules were rearranging between layers. This gave us an indication that the reorganization proceeds by a bulk folding of the layers, which is consistent with the island morphology.
Cadmium LB films deposited at high pH (approximately 8.5) have a different stoichiometry of one cadmium cation for every fatty acid. These molecules do not undergo a conformational transition, and this leads to a significantly reduced rate of reorganization for these films. This result shows that if we can create LB films that maintain their deposited structure throughout the layers, then we can eliminate the instability of fatty acid salt films.

DD8.13
HYDROTHERMAL SYNTHESES AND STRUCTURAL CHARACTERIZATIONS OF A THREE-DIMENSIONAL MICROPOROUS GALLIUM MANGANESE PHOSPHATE (C₄N₂H₁₂)₂Ga₅(H₂O)Mn₂(PO₄)₈ AND A LAYERED GALLIUM PHOSPHATE (C₆N₂H₁₆)Ga₂(C₆N₂H₁₄)(PO₄)₂(HPO₄). Kuei-Fang Hsu , Chia-Heir Lin, Sui-Lein Wang, Dept of Chemistry, Natl Tsing Hua University, Hsinchu, TAIWAN.

Hydrothermal syntheses of the A/Ga/P/O (A = piperazine, and 1,2-diaminocyclohexane) system has been investigated. Two novel gallium phosphate phases, (C₆N₂H₁₆)Ga₂(C₆N₂H₁₄)(PO₄)₂(HPO₄) (1) and (C₄N₂H₁₂)₂Ga₅(H₂O)Mn₂(PO₄)₈ (2), have been prepared under mild T/P conditions. Phase 1 adopts a layer structure in which protonated amine cations are between layers. The anionic layer is built up of octahedron of GaO₄N₂ and tetrahedra of GaO₄, PO₄ and HPO₄, respectively. Interestingly, the organic amine molecules plays two roles in the formation of phase 1: one half of 1,2-diaminocyclohexane molecules are coordinated to Ga atoms as bidentate ligands and the other half are protonated as templates to the structure. Being the first mixed manganese (II, III) gallium phosphate, phase 2 was obtained using piperazine as a structure-directing reagent. It adopts a 3D open framework structure in which three kinds of polyhedra coexist: octahedron of GaO₆, bipyramid of GaO₅, and tetrahedra of MnO₄, and PO₄. These polyhedra are interconnected via a corner-sharing manner to give a zeolitic framework in which large and straight channels are formed inside the structure. The piperazinium cations are residing in the tunnel at two crystallographic sites such that they are staggering along the channel directions. In this paper, hydrothermal syntheses, crystal structures, and thermal properties of the title compounds will be presented in detail.
 
 
 
 

SESSION DD9: POSTER SESSION:
HYBRID PROPERTIES
Wednesday Evening, April 7, 1999
8:00 P.M.
Salon 7 (M)

DD9.1
FASH ION CONDUCTING SILVER-SILICATE XEROGELS: SYNTHESIS AND STRUCTURAL INVESTIGATIONS. N. Satyanarayana, A. Keith King and B. Rambabu , Southern University and A&M College, Surface Science, Spectroscopy and Solid State Ionics Laboratory, Department of Physics, Baton Rouge, LA.

Silver-silicate based fast ion conducting (FIC) compounds have become increasingly popular in the field of solid state ionic device technologies due to their structural stability and increased ionic conductivity. Among the known preparation techniques, recently, the sol-gel synthesis technology has become a viable and alternate technique for the preparation of toiler made fast ion conducting materials for custom designed ionic devices. In this work, we have made an attempt to synthesize fast ion conducting binary oxide xerogels [(XAg₂O+(1-X)SiO₂) (SS); X=0.1 to 0.9 in steps of 0.1]. Structural properties were investigated by using XRD, IR, DSC, SEM, EDS, WDS and impedance spectroscopy techniques.
Analar grade chemicals of AgNO₃, HNO₃, Si(C₂H₅O), tetraethylorthosilicates (TEOS), C₂H₅OH, supplied by Aldrich Co., USA, and double distilled water were taken and mixed at different stages. The sol-gels were prepared by mixing the following A and B solutions. Solution A was prepared by dissolving the TEOS in C₂H₅0H and the required amount of H₂0 was added to the solution (TEOS +C₂H₅OH) on continuous stirring. Solution B, prepared by dissolving AgNO₃ in the required quantity of water (H₂O), was added to the solution A under continuous stirring. The sol was then cast in a beaker and allowed to form a gel at 40C. Clear transparent gels were obtained within 72 hours. The gels were then allowed to dry at 40C, in order to obtain the xerogels and were grounded well and made into fine powders. All the compositions of the SS xerogels were characterized to determine the nature, structure and electrical conductivity of each composition of the SS system. Detailed results on SS system will be presented and discussed.
Acknowledgement: B.Rambabu acknowledges the RCS program at LLNL and US DOE-Office of Basic Energy Sciences for supporting this work through a subcontract and a grant.

DD9.2
SYSTEM FOR PRIMARY BATTERIES: SOL-GEL SYNTHESIS AND CHARACTERIZATION. N. Satyanarayana ¹ and B. Rambabu, Southern Univeristy and A&M College, Surface Science, Spectroscopy and Solid State Ionics Laboratory, Department of Physics, Baton Rouge, LA; P. Muralidharan, Pondicherry University, Department of Chemistry, Pondicherry, INDIA; R. Patcheammalle and M. Venkateswarlu, ¹Pondicherry University, Department of Physics, Pondicherry, INDIA.

Sol-gel technology has gained interest in the field of superionic conducting materials to synthesize different types of glasses, polycrystalline, ceramic materials in the forrn of monoliths, fine powders, thin films, etc. New superionic conducting materials synthesized through sol-gel technique have received more importance due to their applications of various electrochemical devices. Of which, lithium based solid electrolytes are promising materials for utilization in the solid state batteries. The aim of this work is to synthesize lithiumborophososilicate (LBPS) system by sol-gel process, characterization and study their impedance & battery discharge characteristics. Sol-gels are prepared by mixing analar grade chemicals using the following formula 20Li₂O-80%[0.2P_2O_5+0.8(xB_2O_3+(1-x)SiO_2)], X=0.0 to 1.0 in steps of 0.1. For one of the compositions, 0.1N nitric acid as catalyst, solution A contains tetraethylorthosilicate (TEOS) [Si(OC_2H_5)_4H₅C₂H₄NH₃)₂PbX₄ (X; Br and I, abbreviated as PhE-PbX₄ hereafter) were fabricated on glass substrates by the spin-coating method. The prepared films showed stable exciton absorption with narrow bandwidth and free-exciton emission even at room temperature. However, the films were not stable against the UV-light irradiation. The PhE-PbX₄ films were readily oxidized by that UV-light irradiation in air. In vacuum, the PhE-Pbl₄ films changed to -phenethylamine intercalated Pbl₂ due to the elimination of halogen spices. On the contrary, no degradation was observed for the PhE-PbBr4 films. These results suggested that the light irradiation-induced photochemical reaction was one of the possible reasons for the degradation. To suppress the oxidation and halogen elimination induced by the photochemical reaction, nanocrystalline PhE-PbX₄ doped PMMA films were also fabricated by the spin-coating and subsequent annealing. Although the nanocrystals dispersed in PMMA gradually decomposed by the UV illumination, marked improvement of the photostability was achieved. In conclusion, the photostability can be improved by doping the nanocrystalline PhE-PbX₄ into a PMMA matrix.

DD9.4
OPTICAL WAVEGUIDE OF INORGANIC/ORGANIC HYBRIDS CONTAINING VARIOUS INORGANIC COMPONENTS DERIVED FROM METAL ALKOXIDES. Noriko Yamada , Ikuko Yoshinaga and Shingo Katayama, Nippon Steel Corporation, Advanced Technology Research Laboratories, Kawasaki, JAPAN.

Inorganic/organic hybrid films containing various inorganic components are expected as a host material to incorporate organic photoactive molecules because of the controllability of refractive indices and heat-resistance derived from inorganic components together with the flexibility derived form organic components. Planar optical waveguides of inorganic/organic hybrid films containing various inorganic components were synthesized from diethoxydimethylsilane and metal alkoxides modified with ethyl acetoacetate. Ti, Zr and Ta alkoxides were used as a precursor of the inorganic components. Inorganic/organic hybrid films were prepared on a quartz glass substrate by spin-coating, followed by drying and heat-treating. The thickness of the hybrid films was 0.60-0.78 m. The hybrid films containing inorganic components derived from Ti, Zr and Ta alkoxides have 1.65, 1.55 and 1.64 in refractive index of  = 633 nm, respectively. The hybrid films showed relatively low values of the optical losses and also small in-plane scattering as a planar waveguide, although they were not prepared in a clean room. The optical loss values of the hybrid films containing inorganic components derived from Ti, Zr and Ta alkoxides were 6.19, 5.16 and 12.08 dB/cm, respectively.
Research supported lay NEDO, under the Synergy Ceramics Project of the ISTF program promoted by AIST, MITI, Japan.

DD9.5
PHOTOELECTRIC PROPERTIES OF MATERIAL OF N,N'-BIS(4'-AMINOPHENYL) -1,4-QUINONENEDIIMINE DOPED WITH HETEROPOLY ACID. Gong Jian, Yang Ji-Hua, Gui Xiu-Jun, Su Zhong-Min, Qu Lun-Yu , Department of Chemistry, Northeast Normal University, Changchun, CHINA.

Polyaniline is a kind of important photoelectric material because of its potential application in fields such as conductivity, LED and so on. Recently, the aniline oligomer is obtaining much more attention due to the structure and size advantages. In this paper, we have synthesized aniline oligomer with different doping heteropoly acid (H₄SiW₁₂O₄₀) and investigated the effect of doping on their UV-Vis absorption spectra and fluorescence properties. The doping and dedoping process of the aniline oligomer was investigated via UV-Vis spectra, pH=5.5 was turning point of doped and dedoping.The band at 572nm disappeared and the bands at 268nm, 412nm, and 771nm appeared after the aniline oligomer was doped. In a certain range, the doping is favorable for a increase of intensity of the fluorescence emission band at 860nm, although the corresponding characteristic absorption band (572nm) is weakened. And at the same time, the fluorescence emission in Vis region (ca. 640nm) is observed, which is caused by the new electronic transition band induced by the doping effect of heteropoly acid. All of these suggest that the aniline oligomer doped with heteropoly acid as a new type light emitting material have an attractive prospect. LED of the new material is being exploited.

DD9.6
HIGHLY ELECTRICAL CONDUCTIVITY OF HYBRID LANGMUIR-BLODGETT FILMS OF TRANSITION METAL DICHALCOGENIDE AND AMPHIPHILIC CATIONS. Hiroaki Tachibana , Joint Research Center for Atom Technology (JRCAT) and National Institute of Materials and Chemical Research, Tsukuba, JAPAN; Yasushi Yamanaka, Mutsuyoshi Matsumoto, National Institute of Materials and Chemical Research; Reiji Kumai, JRCAT, Tsukuba, JAPAN; Yoshinori Tokura, JRCAT and University of Tokyo, Tokyo, JAPAN.

Layered transition metal dichalcogenide MX₂, where M is a transition metal and X is S or Se, have been extensively investigated for their interesting electrical properties such as superconductivity and their application as cathode materials for rechargeable high-energy-density lithium batteries. A variety of organic compounds such as polymers can be intercalated into the layered structures. The organic-inorganic hybrid materials can show hybrid physical and chemical properties. In this paper, we present the formation of the hybrid alternate layered Langmuir-Blodgett (LB) films of an amphiphilic ammonium cation and a transition metal dichalcogenide. The hybrid layered LB films were prepared as follows. Single molecular layers of MX₂ dispersed in water were prepared by intercalation of Li into MoS₂, followed by exfoliation in water. A convenient method using n-butyllithium (n-BuLi) in hexane was used as the intercalation agent. Chloroform solution of the amphiphilic cations was spread onto suspension of single layers of MX₂. The hybrid monolayer was transferred using the LB method onto solid substrates. The electrical conductivity of the hybrid LB films of MoS₂ and amphiphilic cations was above 100 Scm^-1 at room temperature and was very stable. The condcutivity depended on the concentration of MoS₂ dispersed in water, the amphiphilic cation, and the transition metal dichalcogenide. The optical properties of the hybrid layered LB films will also be described.

DD9.7
NANOSCOPICALLY DESIGNED HYBRID DUMBBELL POLYMERS FOR HIGH PERFORMANCE APPLICATIONS. Derek Lincoln , Richard Vaia, Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson AFB, OH; Matthew Marrocco, Aaron Adler, Maxdem, Inc., San Dimas, CA; Traui Walker, Timothy Haddad, Propulsion Directorate, Air Force Research Laboratory, Edwards AFB, CA.

Recent advances in the synthesis of high molecular weight polyparaphenylenes have led to the production of a new class of rigid-rod polymers with excellent isotropic mechanical properties and processability. Such polymers have been shown to possess an isotropic tensile and flexural modulus of nearly three times that of common engineering polymers and retain a high storage modulus well above Tg. These polymers also display good melt processability and good solubility in a wide variety of organic solvents making them promising for use in a wide range of engineering applications. Likewise, recent investigations of polyhedral oligomeric silsesquioxane (POSS) macromers have also shown polymeric materials displaying enhanced thermal stability. POSS macromers possess inorganic silica-like cores with seven inert and one reactive organic group. Polymerization at the single reactive site leads to the formation of a linear polymer with nanosized inorganic pendant groups. Thermolysis studies on such polymers have shown that they undergo a polymer-ceramic conversion process forming SiOxCy chars rather than burning. The work presented here describes the behavior of substituted polyparaphenylenes with various POSS macromers (chlorophenyl or chlorobenzyl POSS at 5 and 10wt%) incorporated as end-groups. This work includes studies of these polymers using dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), x-ray scattering techniques, and transmission electron microscopy (TEM) with the end goal of understanding the thermolysis and ablative properties.

DD9.8
OPTICAL CHARACTERISTICS OF SILICA-PEO HYBRID THIN FILMS. Oun-Ho Park , Young-Joo Eo, Yoon-Ki Choi and Byeong-Soo Bae, KAIST, Dept of Materials Science and Engineering, Lab. Optical Materials and Coating, Taejon, KOREA.

Silica-poly(ethylene oxide)(PEO) hybrid materials which have both silica network and polymer network are synthesized from hydrolysis, condensation and polymerization of -glycidoxypropyltri- methoxysilane(GPTS). Polymerization of the epoxy groups to poly(ethylene oxide) units is achieved by using 1-methylimidazol as a thermal curing agent or mixed triarylsulfonium hexafluorophosphate salt as a UV curing agent. The structural change of the hybrid solution is investigated by using NMR spectroscopy. The microstructure of silica-PEO hybrid film is changed according to the degree of polymerization controlled by the thermal or UV curing conditions. The epoxide polymerization is confirmed by using FT-IR and differntial scanning calorimetry(DSC). The hybrid material is densified due to the epoxide polymerization by thermal or UV curing as well as silica condensation. The optical properties such as refractive index, extinction coefficient and optical transmittance of the silica-PEO hybrid films are measured as functions of curing conditions. The variation of the optical characteristics depending on the epoxide polymerization will be discussed.

DD9.9
PHOTOELECTROCHEMICAL PROPERTIES OF POLYANILINE-CdS FILMS. D. Gonccalves , Inst Física de São Carlos, Univ São Paulo, São Carlos, SP, BRAZIL; L.O.S. Bulhões, Dept de Química, Univ Federal de São Carlos, São Carlos, SP, BRAZIL.

CdS particles with sizes ranging from 50 to 100 nm were synthesized by chemical precipitation of Cd(NO₃)₂ and Na₂S in aqueous solution. PANI-CdS films were obtained on platinum electrodes by cyclic voltammetry or electrolysis of aniline in the presence of a CdS suspension. According to the observed by scanning electronic microscopy, PANI-CdS films showed a porous structure with CdS nanoparticles incorporated in the whole surface of the film. Electrochemical impedance and photoelectrochemical measurements were made on PANI and PANI-CdS films since both results allow determining their semiconductor properties. For a typical semiconductor, the capacitance of the space-charge layer (C_SC) obeys the Mott-Schottky equation. Mott-Schottky plots were made on PANI and PANI-CdS films in the region of the first redox process of PANI. In the range of frequencies from 1 Hz to 50 kHz, the contributions to C_SC are electronics and mass transport effects are not significant. C_SC values for both films presented little variations (in order of 10²¹ cm^-3) with film thickness and preparation method (cyclic voltammetry or electrolysis). PANI and PANI-CdS were also studied in dark and under UV and visible light. A time of 20s was obtained by photocurrent measurements being associated with the occurrence of photothermal processes. In the presence of Na₂C₂O₄ (an efficient, irreversible hole scavenger), this value decreased to 2-3s. Higher photocurrent values were obtained for PANI-CdS films as a result from photoexcitation of the polymer and/or colloidal CdS particles, which do not (i) represent a new phase and (ii) favor a charge movement discontinuity. The quantum efficiency of the photocurrent at more positive potentials is about 6x10^-4, a typically low value since (i) recombination is the dominant process in the oxidized polymer or (ii) a highly efficient process occurs for a small number of photons absorbed by the CdS nanoparticles.

DD9.10
SURFACE MODIFICATION OF POLYMER WITH GRAFTING AND COATING OF SILANE HYBRIDS AND THEIR BIOACTIVITY. Masaaki Kubo , Kanji Tsuru, Satoshi Hayakawa, Akiyoshi Osaka, Okayama Univ, Faculty of Engineering, Biomaterials Lab, Okayama, JAPAN; Chikara Ohtsuki, Nara Institute Science and Technology, Graduate School of Materials Science, Nara, JAPAN; Seisuke Takashima, Okayama Univ, Co-Operative Reserch Center, Okayama, JAPAN.

Materials involving both silanol groups and Ca2+ ions show ability of bonding to living tissue or bioactivity: bone-like apatite is deposited on such materials when soaked in a body environment, and the bone cells are firmly attached to the apatite layer. One can provide polymers with the bioactivity by modifying the surface with those chemical species. In the present study, a silane coupling agent was grafted to such organic polymers as HDPE, polyamide or PVC. Ormosil-type film was then coated via sol-gel processes on the grafted surface. Bioactivity was examined by using a simulated body fluid. Bonding strength between the substrate and the coating film will be discussed.

DD9.11
ELECTRONIC PROPERTIES OF THE MODEL ORGANO- METALLIC POLYMER [M-C(C(N)]n (M = Cu(I), Ag(I), Au(I). Su Zhong-Min , Wang Rong-Shun, Che Chi-Ming, Institute of Functional Material Chemistry, Department of Chemistry, Northeast Normal University, Changchun, CHINA.

The organometallic complexes of transition metal M = Cu(I), Ag(I), Au(I) with d10 electronic configuration have abundant optical, electronic and magnetic properties, so it is possible to prepare the high functional organometallic polymer materials by coordinating (-conjugated organic molecules with d10 metals. According to the experimental structures, the model polymers [M-C(C(N)]n are built up and calculated by quantum chemistry methods. It is indicated from theoretical analysis that the organometallic polymer would have comparable conductivity when the interaction exists between metals and pi electrons of different chains.

DD9.12
POROSITY IN POLYSILSESQUIOXANE XEROGELS. Duane A. Schneider , Brigitta M. Baugher, Douglas A. Loy, Encapsulation and Foams Department, Sandia National Laboratories, Albuquerque, NM.

Polymerization of organotrialkoxysilanes is a convenient method for introducing organic functionality into hybrid organic-inorganic materials. However, not much is known about the effects of the organic substituent on the porosity of the resulting xerogels. In this study, we prepared a series of polysilsesquioxane xerogels from organotrialkoxysilanes (RSi(OR')₃) with different organic groups (R = H, Me, Et, dodecyl, hexadecyl, octadecyl, vinyl, chloromethyl, cyanoethyl). Polymerizations of the monomers were carried out under a variety of conditions, varying monomer concentration, type of catalyst, and alkoxide substituent. The effect of the organic substituent on the sol-gel process was often dramatic. In many cases, gels were formed only at very high monomer concentration and/or with only one type of catalyst. All of the gels were processed as xerogels and characterized by scanning electron microscopy and nitrogen sorption porosimetry to evaluate their pore structure.

DD9.13
NEW MATERIALS WITH IMPROVED PROPERTIES FROM POLYMER-CERAMIC NANOCOMPOSITES. Frank-Dieter Kuchta , Dutch Polymer Institute, Eindhoven, THE NETHERLANDS; Hartmut R. Fischer, Lawrence F. Batenburg, TNO-TPD Materials Research & Technology, Eindhoven, THE NETHERLANDS.

The aim of the present study is to exhibit the potentials of new materials based on polymer-ceramics and to understand the action of nano-scaled inorganic particles within a polymer matrix with respect to the ultimate material properties. From the fundamental work of researchers at Toyota Central Research and Development Laboratories on nanocomposites based on polyamide-6 and layered silicates (i. e. clay minerals) it became apparent, that due to the high aspect ratios of inorganic nano-scaled particles materials are obtained that show improved mechanical, thermal and barrier properties without a significant loss of optical transparence, toughness or impact strength. Within the present investigation the effect of an external confinement introduced by highly anisotropic silicate layers of organically modified clay minerals on nanocomposite properties and crystal structure has been studied on polyamide-6, polyamide-11, polyethylene and polypropylene. The composites were prepared both by in situ polycondensation and by reactive blending via melt extrusion. All nanocomposites exhibit a homogeneous distribution of individual silicate layers within the host polymer at low clay content. In polyamide-11 crystallization the lamellar thickening growth is reduced as an effect of external constrained of the silicate layers in the host polymer. As a result, the nanocomposites based on polyamide-11 show an enhanced thermal stability and tensile modulus. Furthermore results on thermal and mechanical properties of polyethylene and polypropylene nanocomposites are presented where block-copolymers have been used to achieve homogeneous intercalation of layered silicates within the host matrix. A new application of polymer-clay nanocomposites applied in the pigment field will be pointed out.
 

SESSION DD10: BIOMEDICAL APPLICATIONS OF
HYBRID MATERIALS
Chair: Lorraine F. Francis
Thursday Morning, April 8, 1999
Salon 11/12 (M)

8:30 AM *DD10.1
MICROPATTERNED POLYMER SUBSTRATES FOR CONTROLLING NERVE CELL GROWTH. Kathryn Uhrich , Kristine Schmalenberg, Rutgers University, Department of Chemistry, Helen Buettner, Rutgers University, Department of Chemical & Biochemical Engineering, Piscataway, NJ.

Microlithography is a technique that has long been used in the computer industry for patterning microchips. Recently, this method has been applied towards patterning inorganic substrates (e.g., glass) for neuron growth. Because most cells need a directional scaffold to promote phenotypical and genotypical expression, microlithography can provide a precise pattern along which cells can align, function and grow. Although there are many groups using inorganic substrates, there is little work on organic or even polymeric substrates For this study, biocompatible polymers were compressed into thin films, then patterned by adapting conventional microlithographic techniques. The patterned areas were filled with laminin to encourage neuronal growth. Using fluorescence microscopy, neuronal alignment on the patterned surfaces was observed. The polymeric substrates were also evaluated using x-ray photoelectron spectroscopy to ensure that the lithographic process did not significantly change the polymer surface.

9:00 AM DD10.2
BIO-INORGANIC COMPOSITES FOR SENSOR APPLICATIONS. R.B. Bhatia , K.S. Butler, University of New Mexico, Albuquerque, NM; C.J. Brinker, C.S. Ashley, Sandia National Laboratories, Albuquerque, NM.

Considerable work has been done to date establishing the retention of bio-activity of enzymes, anti-bodies and whole cells immobilized within silica gel matrices in liquid media. The demonstration of enzyme-based molecular recognition and enzyme-catalyzed dye production within silica hosts is promising for potential bio-sensor applications. However the main challenge to make bio-sensors is to maintain the sensor selectivity and sensitivity over the range of temperatures and humidity encountered in real world environments. Here we report bio-activity of enzymes in xerogels and aerogels. A two step aqueous sol-gel procedure using sodium silicate as the precursor was used to encapsulate the enzymes, glucose oxidase and peroxidase, and dye precursors. These gels were then equilibrated at varying humidities for three weeks. The sensor scheme involving the reactions of the enzymes to form a colored product from the dye precursors was demonstrated within the dried gels. Retention of bio-activity was also shown in the corresponding aerogels, prepared from the wet gels by supercritical extraction. Further a vapor phase bio-inorganic sensor was prepared by encapsulating alcohol oxidase in the silica host matrix.

9:15 AM DD10.3
HIGH SURFACE AREA THIN FILMS FOR DNA ARRAYS. Marc Glazer , Curtis W. Frank, Dept of Chemical Engineering, Stanford Univ, Stanford, CA; Richard P. Vinci, Dept of Materials Science, LeHigh Univeristy, Bethlehem, PA; Jody Beecher, Glenn McGall, Affymetrix, Santa Clara, CA; John Bravman, Dept of Materials Science, Stanford Univ, Stanford, CA.

DNA Arrays offer a combinatorial approach to DNA analysis which is likely to have a major impact on biological and genetic research. Probe based hybridization is carried out in a layer of DNA which is attached to an inorganic substrate (usually glass). Short strands of DNA (probes) are grown and patterned on a surface using solution chemistry and photolithography. Unidentified strands of DNA (target) are then analyzed by hybridization to the arrays. As in the semiconductor industry, a key to the future development of the arrays is feature size. To achieve smaller features, we have investigated high surface area thin films which effectively increase the degree of hybridization for a 2-D area. Thin inorganic films have been created by annealing and etching a phase-separating sodium borosilicate glass (7% Na₂O, 26% B₂O₃, 67% SiO₂ by wt.) that separates into soluble (sodium, boron rich) and insoluble (silicon rich) phases during annealing. The soluble phase is then leached with HF acid, creating a thin porous surface layer. The surface is then stained and patterned with short, fluorescently-labeled probes using the process and equipment provided by Affymetrix. A substantial gain in signal from this process is observed using confocal fluorescence microscopy. The gain is compared to the actual density of available sites, which is determined by attaching probes to the surface, cleaving them in solution, and quantifying with chromatography. The effects of optical scattering, fluorescence quenching, and the implications for future work on hybridization of full length probes within the matrix are discussed.
 

SESSION DD11: ELECTRONIC PROPERTIES
AND APPLICATIONS
Chair: Lorraine F. Francis
Thursday Morning, April 8, 1999
Salon 11/12 (M)

10:00 AM DD11.1
FABRICATION OF NANOMETER SIZE SILICON WIRE PATTERNS WITH A SILVER NANOCRYSTAL WIRE SHADOWMASK. Sung H. Choi , Kang L. Wang, UCLA, Electrical Engineering Dept, Los Angeles, CA; Martin S. Leung, Gary W. Stupian, Nathan Presser, The Aerospace Corp, Electronics Technology Center, El Segundo, CA; Sung W. Chung, Sang H. Kim, James R. Heath, UCLA, Dept of Chemistry and Biochemistry, Los Angeles, CA; Gil Markovich, Tel Aviv Univ, School of Chemistry, Tel Aviv, ISRAEL.

Previously, we showed a new method of using silver (Ag) nanocrystal wires as a shadowmask to produce nanometer-size photoresist wire patterns. In this abstract, we describe the use of the same technique to fabricate nanometer-size silicon (Si) wire patterns. In this technique, organically functionalized Ag nanocrystals (2-100nm) can assemble into lamella (wire-like) phases. The width of the wires could be controlled from 20 to 300nm, and for a given set of wires, a narrow distribution of widths 15-25% could be obtained. The wire patterns can be transferred as Langmuir-Scheffer (horizontal lift-off) films to the polymethyl methacrylate (PMMA) coated Si substrates. The height of this nanocrystal pattern was amplified by immersing the substrate in a solution containing decanedithiol followed by immersing the substrate into a hexane/nanocrystal solution. This amplification doubled the height of the wires to about 8nm. The areas occupied by organic ligands between the nanocrystals in the wire decreased through a metallization process-ripening of the nanocrystals by mass transfer between the nanocrystals. The wire patterns were transferred to the PMMA films by spatially selective electron beam exposure on the Ag nanocrystal wire shadowmask. 50nm wide Si wire patterns were formed by a subsequent anisotropic reactive ion etching (RIE) process. Monte Carlo simulation was done to estimate the electron stopping power for the Ag nanocrystal shadowmask at low voltage. This technique allows for the use of low energy electron beam exposure (700V), which reduces the proximity effects and is suitable for low cost and high throughput fabrication of semiconductor nanometer-scale structures.

10:15 AM DD11.2
PROCESSING OF LEAD TITANATE/ORGANIC HYBRID FROM METAL-ORGANIC PRECURSOR. Toshinobu Yogo , Hiroyuki Ukai, Kaoru Tachibana, Wataru Sakamoto, Shin-ichi Hirano, Nagoya Univ., Dept of Applied Chemistry, Nagoya, JAPAN.

Ceramic/polymer hybrids attract growing attentions as new inorganic/organic materials. This paper describes the processing of PbTiO₃/organic hybrid from metal-organic precursor. PbTiO₃(PT) precursor was prepared from lead- organic and titanium alkoxide. IR and NMR analyses of the precursor revealed the formation of double metal-organics in solution. The precursor was hydrolyzed and polymerized under the controlled reaction conditions. The formation conditions of nano-sized PT particles below 100 centigrade were investigated. The crystalline particles in the organic matrix were analyzed by Raman spectroscopy, SAD and EDX. The particle size was found to depend upon the polymerization and hydrolysis conditions. The electro rheological properties of the hybrid were measured. The hybrid was shaped into films by heating under pressure. The dielectric properties of the hybrid film were also evaluated.

10:30 AM DD11.3
ELECTRICAL AND MECHANICAL PROPERTIES OF CARBON BLACK-FILLED POLYMER COATINGS. Jaime C. Grunlan , David Rowenhorst, Lorraine F. Francis, William W. Gerberich, Univ of Minnesota, Dept of Chemical Engineering and Materials Science, Minneapolis, MN.

In carbon black-filled polymer coatings, improved electrical conductivity is often achieved at the expense of mechanical performance. Model carbon black-polymer coating systems were prepared to explore the effects of parameters, such as carbon black loading, polymer modulus, polymer-carbon interfacial adhesion and coating microstructure on electrical and mechanical properties. Coatings with poly(vinyl alcohol) [PVA] and poly(N-vinylpyrrolidone) [PNVP] matrices showed dramatic increases in electrical conductivity at 10-15 vol. carbon black. Beyond the percolation threshold, PNVP composites achieved a peak conductivity of 3 S/cm at 30 vol. carbon black loading, which was an order of magnitude higher than that achieved by the equivalent PVA composite. The elastic modulus, as determined by the Hysitron Triboscope nanoindenter, increased steadily from 3 GPa for PNVP without any filler to 6.5 GPa with 30 vol. carbon black. PVA films followed the same trend but yielded lower moduli at each carbon black concentration. Composite modulus actually decreased beyond 25 vol. carbon black, when tested with a dynamic mechanical analyzer, due to macroscopic defects resulting from exceeding the critical pigment volume concentration (CPVC). Scanning electron microscopy was employed to evaluate the presence of defects at each filler concentration. Interfacial adhesion between carbon and polymer was evaluated using force curves obtained from atomic force microscopy and Hysitron nanoindentation with carbon-coated tips probing polymer coatings.

10:45 AM DD11.4
STRUCTURE AND PROPERTIES OF POLYANILINE- INTERCALATED GRAPHITE OXIDE NANOCOMPOSITE. Pinggui Liu, Kecheng Gong , South China University of Technology, Polymer Structure & Modification Research Lab, Guangzhou, CHINA.

Recently we reported the synthesis of -MnO₂-polyaniline nanocomposite^[1], whose electrical conductivity and thermal properties had been greatly improved. Graphite oxide, a typical pseudo two-dimensional solid in bulk form, possesses hydroxyl, carbonyl and ether groups as functional groups, which cause the low electrical conductivity of graphite oxide. These groups also make graphite oxide easily absorb polar molecules and polar polymers to form nanocomposites, especially by self-assembly in Fendle's paper^[2]. In this work, an exfoliation/absorption process was used to synthesize polyaniline-intercalated graphite oxide nanocomposite. After reaction, a multiphase product was obtained, this was proved by XRD, where the strong (001) x-ray diffraction peak of graphite oxide was completely replaced by some broad, low-intensity deflection between 12-30. FTIR, UV spectra had shown the existence of polyaniline in form of emeraldine salt. The electrical conductivity of polyaniline-graphite oxide nanocomposite had been greatly improved, especially when chemically reduced by aqueous hydrazine hydride solution, the electrical conductivity of the reduced polyaniline-graphite oxide was more than 1 order of magnitude higher than that of polyaniline-graphite oxide at ambient temperature, reaching from 1.4x10^-3 S/cm to 3.8x10^-2 S/cm. Similarly, the improved thermal stability was also been proved by thermal analysis.
^[1] K.C. Gong, W. Zhang, ABSTRACTS of 1997 MRS Fall Meeting, No3.9, 332, Boston.
^[2] N.A. Kotov, I. Dekany, J.H. Fendler, Adv. Mater., 1996, 8, 637.

11:00 AM DD11.5
MICROWAVE DIELECTRIC CHARACTERIZATION OF POLYSILSESQUIOXANE - POLYANILINE COMPOSITES. J. Obrzut , C.K. Chiang, W.A. Wallace, National Institute of Standards and Technology, Gaithersburg, MD.

The dielectric properties of the new polysilsesquioxane - polyaniline composites have been investigated in the broad band frequency range, up to 20 GHz. The functionalized polyhedral and branched silsesquioxanes were cross-linked with the oxidized emerdaline-base of polyaniline to obtain a material of enhanced dielectric properties with a low loss and higher temperature tolerance. Unlike polyacetylene or poly-para-phenylenevinylene, polyaniline exhibits asymmetric valence states with the Fermi level shifted away from the center of the band gap. The presence of de-localized electronic states with non symmetric charge conjugation at energies less than the band gap can lead to enhanced polarizability extended to optical frequencies. We have investigated the effects of protonation of polyaniline on dielectric permittivity of the composites and compared the results with polymers filled with ferroelectric powders. We have also examined the DC conductivity and low frequency dielectric relaxation behavior in relation to the molecular architecture of the polysilsesquioxane network.

11:15 AM DD11.6
THE ELECTRICAL AND OPTICAL PROPERTIES OF PHENYL-MODIFIED SiO₂ THIN FILMS PREPARED BY SOL-GEL TECHNIQUE FOR MICROELECTRONIC APPLICATIONS. Chandra S. Desu , Swaroop Kaza, Ramakrishna Vedula, Seshu B. Desu, Department of Materials Science and Engineering, Virginia Tech, Blacksburg, VA.

In the present work, we report a systematic study on the effect of phenyl modification on lowering the dielectric constant of SiO₂ thin films. Both pure and phenyl modified SiO₂ thin films have been prepared by sol-gel technique onto n+(100) Si and p-Si substrates. Tetraethoxy silane (TEOS) was used for the preparation of SiO₂ thin films and the phenyl modification was performed by the addition of diphenyl diethoxy silane (DDS) to the precursor solution. The as-deposited films were subjected to annealing treatments at various temperatures in air. The change in the chemical structure with the composition and the annealing temperature was observed by FTIR spectroscopy. The film thickness and the optical properties were measured by spectroscopic ellipsometry. The dielectric and insulating properties were measured using Al top electrodes sputter deposited onto the film surface. The refractive index of the films, measured using ellipsometry indicated a decrease with increasing DDS composition in the precursor solution. Similarly, the dielectric constant was also found to decrease with the phenyl modification. All these results indicate that phenyl modification of SiO₂ is a promising approach towards lowering the dielectric constant.

11:30 AM *DD11.7
MECHANICAL PROPERTIES OF LOW DIELECTRIC-CONSTANT ORGANIC-INORGANIC HYBRIDS. Robert F. Cook , University of Minnesota, Department of Chemical Engineering and Materials Science, Minneapolis, MN.

Spin-on glasses, generated by the condensation of an organic-inorganic hybrid silsesquioxane (SSQ), have great potential as low dielectric-constant semiconductor interconnection materials. After curing and condensation SSQ materials consist of an amorphous, inorganic, -Si-O-Si- bridging network with organic, non-bridging -Si-R side groups. Relative dielectric constants in the range 2.5-3.3 are obtained for SSQ materials, depending on the curing conditions, and compare with 4.0 for conventionally-used fused silica. The non-bridging side groups significantly disrupt the SSQ network, occupying more than 25% of the Si bonds, and lead to materials that are considerably less stiff, hard and tough than fused silica. Perhaps more importantly, SSQ materials have thermal expansion coefficients greater than that of the intended Si substrate and therefore finish curing in a state of residual tension, leading to a susceptibility to stress-corrosion cracking. In this talk the development of properties (dielectric and mechanical) during curing of SSQ spin-on glasses is considered and the properties of hydridi-, methyl-, and phenyl-substituted SSQ materials compared. Various toughening schemes involving both organic and inorganic additions will be discussed.
 

SESSION DD12: MECHANICAL PROPERTIES AND APPLICATIONS
Chair: Lisa C. Klein
Thursday Afternoon, April 8, 1999
Salon 11/12 (M)

1:30 PM *DD12.1
THE ACID-BASE ENERGETICS OF ADHESION IN COMPOSITE MATERIALS. John C. Berg , University of Washington, Dept of Chemical Engineering, Seattle, WA.

Filled polymeric composites are investigated to assess the role of acid-base effects on the adhesion between the filler particle surface and the matrix polymer and on the mechanical properties of the composites. The surface of the filler material is systematically modified using silane coupling agents, and a variety of surface characterization techniques are used to determine their surface energetics and acid-base properties. Adhesion properties are determined by a new direct method in which a single spherical filler particle is embedded into the matrix. The single-particle composite is subjected to uni-axial tension until interfacial failure occurs at one of the poles, yielding the stress at failure and a characteristic cap angle, without edge and end effects. Measured interfacial strengths correlate on one hand with acid-base effects determined independently, and on the other hand with the mechanical properties of highly-filled composites of the same components, as determined in beam deflection tests.

2:00 PM DD12.2
HYBRID ORGANIC-INORGANIC COATINGS BASED ON COLLOIDAL SILICA. M.W. Daniels , L.F. Francis, Univ. Minnesota, Dept. of Chemical Engineering and Materials Science, Minneapolis, MN.

Coatings from ceramic colloids are widely used due to the flexibility and convenience offered by suspensions and the advantages gained from ceramic properties such as hardness and index of refraction. However, ceramic coatings made from colloidal suspensions generally have poor properties (wear resistance, critical cracking thickness, adhesion) unless high processing temperatures or additives are used. Organic additives such as silane coupling agents and binders give coatings the desired mechanical properties. This presentation will focus on studies of how these additives affect the microstructure and properties of colloidal silica coatings. Important coating features studied include porosity, wear resistance, cracking behavior, and adhesion. Microstructure and properties are influenced by composition, pH, processing time and temperature, and components. A better understanding of the effect of these variables is gained through study of the reactions in the coating solution, which occur before and during drying. Adsorption of silane coupling agent was studied and combined with observations of reactions between coupling agents to develop an explanation of how the final microstructure developed. Use of UV-cured cross-linkers was shown to improve wear resistance, while amine crosslinkers increased porosity.

2:15 PM DD12.3
SOL-GEL ANTIFOGGING COATINGS ON POLYMER SURFACES. Hermann Schirra , Thomas Mueller, Helmut Schmidt, Institut fuer Neue Materialien gem. GmbH, Saarbruecken, GERMANY.

Objective of these investigations was the development of polymer surface coatings, which are characterized by a good wettability of water and oleophilic liquids as well as a long term stable antifogging effect. Scratch resistant nanocomposite coatings based on an epoxysilane/methacrylsilane/boehmite system have been chosen as basis material. By an incorporation of nonionic or cationic based hydrophilically active components the hydrophilicity of these systems could be increased with achieving contact angles against water down to 5 and excellent antifogging properties. The best results were obtained, if the hydrophilic components being linked to the backbone as well as surfactants being able to diffuse through the network were used at the same time. The immobilized surfactants provide the basis ambiphilicity of the system and the diffusible components are able to react to hydrophobic as well as to hydrophilic contaminates on the surface. By optimization of the system composition, coatings could be developed with material properties between highly flexible (e.g. for the coating of foils) and abrasion resistant with haze values of 15-20% after 1000 cycles taber-abrasion test (CS 10F, 500 g load). With all substrates (PC, PET, PMMA) excellent adhesion (crosscut >95/100, tapetest as well) resulted after a suitable way of pretreatment (primer, corona, pretreatment, flame). In the case of PMMA a nanocomposite coating material could be synthesized with a crosscut/tapetest >95/100 only with an alcoholic cleaning of the surface. The long term hydrophilicity was proven in a 40C water exposition test. All coatings showed contact angles against water of < 30 ° after 7 and 14 d exposition without any delamination of the coating.

2:30 PM DD12.4
ABRASION RESISTANT ORGANIC/INORGANIC HYBRID SOL-GEL COATINGS ON PLASTICS. C.M. Chan and G.Z. Cao, University of Washington, Department of Materials Science and Engineering, Seattle, WA.

We investigated abrasion resistant organic/inorganic hybrid sol-gel coatings on plastics. Silica network was modified by incorporation of organic components and transition metal oxides so as to modify thermal and mechanical properties of the coatings. Highly dense coatings (up to 99% theoretical density) were obtained using in-situ low temperature (below 150 °C) densification techniques, that included enhanced evaporation of solvent, ultra-violet (UV) irradiation promoted surface condensation, and infrared (IR) assistant structural relaxation. Various surface treatments were applied to achieve good adhesion of sol-gel coatings on plastics. Nanoindentation analysis revealed that the hybrid coatings had a surface hardness of 2.5 GPa, approximately one order of magnitude higher than that of the plastic surface. In addition, ellipsometry and nanoindentation analyses indicated that both the density and hardness varied with the depth of the hybrid coatings.

2:45 PM DD12.5
SOL-GEL HYBRID MATERIALS FOR POWDER COATING TECHNOLOGY FOR TRANSPARENT ABRASION RESISTANT FILMS. S. Sepeur , J. Muhle, H. Schmidt, Institut fuer Neue Materialien gem. GmbH, Saarbruecken, GERMANY.

Sol-gel coating powders were recently prepared by hydrolysis and controlled polycondensation from mixtures of organically modified silanes and organic crosslinking-agents with an optional incorporation of nanoparticles. After evaporation of the solvent or precipitation in an excess of water, drying under vacuum and grinding, solid materials were obtained. The resulting non-sticky powders with a melting range between 85-100C showed thermosetting behavior after thermal densification, which was proved by DSC-measurements. At temperatures between 100-150C the minimum melt-viscosities of the inorganic-organic nancomposites ranged between 0.1-150 Pas. For coating, the powders were employed by a corona-charging spray gun, and transparent dense coatings with thicknesses between 20-40 m were obtained. The powder coatings showed good primerless adhesion to the surface of aluminium sheets (Al 99.5, AlMg₃), which was determined using cross-cut (grade 0/1) and tape test (grade 4B/5B). The surface hardness of the sol-gel powder coatings was well adjustable by use of nanoparticles (universal-hardness: 160-285 N/mm², Buchholz-resistance of indentation: 120-140). In addition the coatings showed an excellent abrasion resistance, which was determined by taber-abraser test (weight loss method). After 1000 cycles of abrasion with certain wheels (CS-10 F), the material loss ranged only between 7-14 mg. The corrosion resistance of the coatings was examined by salt spray test. After 2000 h in the test chamber the coated aluminium sheets (Al 99.5 and AlMg₃) showed little formation of blister (m1/g1), but no infiltration at the scratch and no reduction of the adhesion after the loading in the corrosive medium, which was proved by cross-cut (grade 0/1) and tape test (grade 4B/5B). The running outdoor weathering measurements (location: Uni-Campus Saabruecken, position: south) provided no change of the coating appearence and no infiltration at the scratch after an exposure time of 2400 h.

3:30 PM DD12.6
TEAR STRENGTHS OF POLY(DIMETHYLSILOXANE) NETWORKS REINFORCED WITH IN-SITU PRECIPITATED SILICA. Chandima Kumudinie, James E. Mark , Department of Chemistry and the Polymer Research Center, The University of Cincinnati, Cincinnati, OH.

The tear strengths of in-situ filled poly(dimethylsiloxane) (PDMS) networks were investigated using trouser-tear tests. The filled PDMS networks were prepared by the simultaneous curing and in-situ precipitation technique, the silica reinforcing phase being obtained by the hydrolysis and condensation of tetraethylorthosilicate present in excess of that required for the chain end-linking process. Transmission electron micrographs showed well dispersed and unagglomerated silica particles, and thermogravimetric analysis indicated that the silica particles gave some improvements in thermal stability. In the tearing tests, stick-slip tearing was observed at higher rates, especially for the filled networks. The tear strengths were found to increase with increase in the amount of silica incorporated, with the largest increases occurring at the lower silica contents.

3:45 PM DD12.7
MECHANICAL PROPERTIES OF SOLUBLE POLYMER/SILICA GEL HYBRIDS. L.C. Klein , J. Van Wert and C.L. Beaudry, Rutgers University, Ceramic & Materials Engineering, Piscataway, NJ.

Strengths have been measured for silica gels prepared with poly(ethylene oxide) (PEO) and poly(vinyl acetate) (PVAc). The modulus of rupture was determined using standard three-point bending in a mechanical tester. The samples were prepared by mixing tetraethylorthosilicate with the polymers dissolved in water (PEO) or water/ethanol(PVAc). Molecular weights between 200 and 8000 were used for PEO. Substitutions of the polymer for silica represented between 5 and 50 on a weight basis. Those compositions that were transparent were selected for testing. Samples that were translucent or opaque were indicative of phase separation, and for that reason, were not suitable for testing. All samples were allowed to gel in plastic tubes. The tubes were capped initially, but the caps were removed after specified periods of aging, from 1 to 24 hours. All samples were thoroughly dried. In these systems, the interactions between the polymer and the silica network are largely through hydrogen bonding, between ether oxygens in PEO and silanols and between hydroxyls in PVAc and silanols. The extent of the bonding increases with increasing aging time, as indicated by an almost linear increase in the modulus of rupture. The increase for PEO was greater than for PVAc. Among PEO samples, the strengthes were higher for higher molecular weights at the same weight fraction, but the increase with time was about the same. The pH and the how it was controlled had some effect as well. Most samples broke in the middle and showed brittle fracture. Some samples showed slight plasticity during failure. Both the choice of polymer and processing conditions influenced the strength of these hybrids.

4:00 PM DD12.8
VISCOELASTIC RESPONSES OF INORGANIC-ORGANIC HYBRIDS POLYMERS. Andre Lee , Michigan State University, Dept. of Materials Science and Mechanics, E. Lansing, MI.

The properties of nano-structured plastics are determined by complex relationships between the type and size of the nano-reinforcement, the interface and chemical interaction between the nano-reinforcement and the polymeric chain, along with macroscopic processing and microstructural effects. In this paper we investigated the thermal and viscoelastic property enhancement on crosslinked epoxy using two types of inorganic nano-reinforcements, namely organoion exchange clay and polymerizable polyhedral oligomeric silsesquioxane (POSS) macromers. Glass transitions of these nano-composites were studied using differential scanning calorimetry. Small strain stress relaxation under uniaxial deformation was examined to provide insights into the time-dependent viscoelastic behavior of these nano-composites. Since the size of POSS macromer is comparable to the distance between molecular junctions, hence as we increase the amount of POSS macromers, the glass transition temperature, Tg, as observed by DSC increase. However for epoxy network reinforced with clay, we did not observe any effect on the Tg due to the presence of clay reinforcements. In small strain stress relaxation experiments, both types of reinforcement provided some enhancement in creep resistance, namely the characteristic relaxation time as determined using a stretched exponential relaxation function increased with the addition of reinforcements. However, due to different reinforcement mechanisms, enhancement in the instantaneous modulus was observed for clay-reinforced epoxies, while the instantaneous modulus was not effected in POSS-epoxy nano-composites.

4:15 PM DD12.9
PREPARATION AND PROPERTIES OF PVC-SILICA COMPOSITES USING DIFFERENT CATALYSTS VIA SOL-GEL PROCESS. Khan M. Asif , Kansas State University, Dept of Chemistry, Manhattan, KS; M.I. Sarwar and Z. Ahmad, Dept of Chemistry, Quaid-i-Azam University, Islamabad, PAKISTAN.

Novel micro-composites of Polyvinyl chloride (PVC) and silica were prepared using sol-gel technique. Different catalysts were used during the hydrolysis/condensation of tetraethylorthosilicate (TEOS) for the in-situ generation of silica network in the PVC matrix. Thin and transparent films were obtained by casting and solvent evaporation method. Mechanical properties of these films up to 15 wt.% silica contents using different catalysts were studied. The results showed an increase in the Young's modulus, length at rupture and toughness of the unplasticised PVC. However, the stress at yield point and stress at rupture decreased with the addition of silica contents. Scanning electron microscopy (SEM-EDAX) studies were also performed on the samples.
 
 
 
 

SESSION DD13: OPTICAL PROPERTIES AND APPLICATIONS
Chair: Hyunjung Shin
Friday Morning, April 9, 1999
Salon 11/12 (M)

8:30 AM *DD13.1
ORGANIC-INORGANIC HYBRID MATERIALS PROCESSING AND APPLICATIONS. Helmut K. Schmidt , Institut fuer Neue Materialien, Saarbruecken, GERMANY.

Organic-inorganic hybrid materials have become an interesting group of new materials which now are entering the field of industrial application. This has been realized for the first level hybrids with molecular networks, and is now being realized with the second level hybrids with mesoscopic scales. The combination of first and second level hybrids are of interest since solid state physical properties attributed to nanoparticles (or colloids) can be introduced into the materials which still show high optical transparency. So-called polymerizable nanoparticles have been developed by in-situ coating of sol-gel derived colloids from SiO₂, TiO₂, ZrO₂ with polymerizable grouping containing ligands and matrix compatible nanoparticles have been synthesized by coating them with organofunctional groupings fitting to polymeric matrices (ZrO₂, ITO). These particles have been used for the fabrication of UV curable or thermally curable interference multilayers, for the fabrication of volume holograms, grated index lenses and highly abrasive UV-curable coatings for plastics. In addition to the in-situ preparation of the nanoparticles by sol-gel reactions, it also was possible to produce nanoparticles by chemical - optional including hydrothermal - processing and surface modification afterwards in form of redispersible powders, as shown with ZrO₂ and ITO. The use of ITO nanoparticles in hard coatings based on epoxy silane/boehmite compositions led to IR absorption layers with an effective energy flow reduction to about 50, and by use of ZrO₂ particles, refractive index matching hard coatings for ophthalmic applications have been obtained.

9:00 AM DD13.2
PHOTOCHROMIC ORGANIC-INORGANIC HYBRID NANOCOMPOSITE HARD COATINGS WITH FAST SWITCHING PROPERTIES. M. Mennig , K. Fries and H. Schmidt, Institut fuer Neue Materialien gem. GmbH, Saarbruecken, GERMANY.

A sol-gel hybrid coating system has been developed, which is based on an epoxysilane as network former, different bisepoxides as spacer, organic amines as thermal cross-linker and surface modified ceramic nanoparticles as filler. The compatibility of the matrix systems has been tested with about 30 commercially available photochromic dyes and thus the preparation of photochromic coatings with neutral tints is possible by mixing different dyes. Photochromic coatings with blue, yellow, red, green, violet and neutral tints were prepared on flat PC (polycarbonate), curved CR 39 (allyl substituted polycarbonate) substrates and PET-foil (polyethylenterephthalate) by spray and spin coating respectively and cured for 2 h - 5 h at 80C - 130C and on different kinds of paper by spray coating and air curing. The photochromic coatings show the following properties: the transmittance changes reversibly between 80 and 20 with half fading times of about 2 s - 20 s (comparable to the half fading time of the appropriate dye in ethanolic solution) after UV irradiation for 15 s with 10 mW/cm². The coatings are stable against organic solvents and show a scratch hardness of about 15 g (scratch test with Vickers indenter, coating thickness 10 m). The addition of only 3 wt SiO₂ nanoparticles increases the scratch resistance of the coatings to about 30 g without changing the fast kinetics of the incorporated photochromic dye(s). The long term stability of the photochromic dye(s) in the matrix system has been considerably improved by the introduction of additives like antioxidants, HALS (Hindered Amine Light Stabilizer) and UV stabilizers. The half lifetime (decay to 50 of the initial photochromic intensity) of a blue spirooxazine dye thus could be increased from 20 hours in a dry suntest (75 mW/cm²) without any additive up to 200 hours with an UV absorber (Tinuvin 327) as a stabilizer, which is assumed to be sufficient for ophthalmic and many decorative applications.

9:15 AM DD13.3
SOL-GEL AR MULTILAYER COATINGS THROUGH UV-POLYMERISABLE CERAMIC NANOPARTICLES. M. Mennig, P.W. Oliveira , H. Schmidt, Institut fuer Neue Materialien gem. GmbH, Saarbruecken, GERMANY.

A new synthesis and processing route to multilayer interference coatings on plastic (like PMMA, polycarbonate and polyester) and glass substrates has been developed. For this purpose alcoholic sols of surface modified (3-glycidoxypropyl trimethoxysilane, GPTS) SiO₂ - and TiO₂ nanoparticles with particle sizes of 10 nm and 4 nm respectively were synthesized by acid catalysed hydrolysis and condensation of the appropriate alkoxides. In order to control the particle growth and to avoid agglomeration GPTS was added as a surface modifier. By the combination of index matching and photopolymerization, interference filters have been fabricated. The interference coatings on polycarbonat show excellent adhesion (GT 0) to the substrates and cause a promising improvement in the mechanical properties of the substrate. The interference coatings do not show delamination or defects after boiling water test (H₂O + 5 wt NaCl, 1 h). The mechanical and optical properties of the interference filter were not changed after sun test by 760 W/m² and 275 h. An antireflecting (AR) coating filter with 3 quarterwave layers and an NIR reflective interference filters with 5 layers were produced on float glass substrates. Each layer was deposited by dip- or spin-coating with subsequent UV-curing with an energy density of 2.5 J/cm², and the layer stack was thermally densified at 450C for 10 min. 80 cycles of rubber test without damage could be obtained. The mechanical and optical properties of the interference filters did not change after sun test with 760 W/m² for 320 h.

9:30 AM DD13.4
FABRICATION OF GRIN LENSES BY CONTACTLESS ELECTROPHORETIC GRADIENT FORMATION IN TRANSPARENT NANOCOMPOSITES. P.W. Oliveira , M. Mennig, H. Schmidt, Institut fuer Neue Materialien gem. GmbH, Saarbruecken, GERMANY.

A new approach to effective radial gradient refractive index (GRIN) lenses has been developed. It is based on the electrophoresis of ZrO₂ and SiO₂ nanoparticles with opposite surface charges (-potential) in a solvent free organic-inorganic hybrid matrix, synthesized from tetraethylene glycol dimethacrylate (TEGDMA), methacryl silane (MPTS) and a complex of zirconium n-propylat (ZR) with methacrylic acid (MA). A DC-electric field of 200 V/cm is applied by a set of ring electrodes on top and bottom of a cylindrical mold containing the matrix sol. The refractive index profile is measured in situ as a function of time by interferometry. The refractive index profile can be conserved by photopolymerisation of the matrix. The resulting concentration profiles of ZrO₂ and SiO₂ are calculated by computer simulation based on electrophoretical diffusion theory and they are measured by EDX analysis, showing excellent agreement to the theoretical results and a parabolic refractive index gradient is obtained in very good approximation. By this method it is possible to obtain 1 cm radial GRIN lenses with a =0.07 within 5 h.

9:45 AM DD13.5
SOL-GEL DERIVED TITANIA/ORMOSIL COMPOSITE THIN FILMS FOR OPTICAL WAVEGUIDE APPLICATIONS. Wenxiu Que, Y. Zhou, Y.L. Lam, Y.C. Chan, C.H. Kam and H.X. Zhang , School of Electrical and Electronic Engineering, Nanyang Technological University, SINGAPORE.

In this paper, we report the preparation of high optical quality sol-gel waveguide films based on a newly developed recipe to incorporate organic molecules into the inorganic sol-gel glass matrix. The film is derived from a sol that has a high titanium content in an organiclly modified silane (ORMOSIL), namely, -Glycidoxypropyltrimethoxysilane. We have shown that using spin-coating or dip-coating and low temperature baking, a single coating layer can have a thickness of more than 1 . When such a single layer film is deposited on a microscope glass slide or a piece of silicon with a buffer-cladding layer, it is able to support the guiding of optical waves. We have characterized the film using atomic force micriscopy, X-ray diffractometry, thermal gravimetric analysis, and Fourier transform infrared spectroscopy and have studied the properties of the waveguide film, including the microstructural properties, the chemical bonding properties, and the optical properties. Based on these experimental results, we found that a heat-treatment at a temperature below 200C is necessary to attain a dense film with low absorption or high tranmission in the visible and near infrafed range. It has also been noted that a purely inorganic and crack-free silica-titania film can be obtained after baking the titania-ORMOSIL composite film at 500C or higher. At the conference, we will present the details of our study and discuss the implications of our research.

10:30 AM DD13.6
PHOTOPHYSICAL PROCESSES IN HYBRID MATERIALS OF CONJUGATED POLYMERS AND DYE-SENSITIZED TiO₂. Thomas K. Daeubler , Ullrich Scherf, Dieter Neher, Max-Planck-Institute for Polymer Research, Mainz, GERMANY; Steffen Pfeiffer, Hans-Heinrich Hoerhold, Univ. Jena, Inst. for Organic Chemistry and Macromolecular Chemistry, Jena, GERMANY; Ireneusz Glowacki, Jacek Ulanski, Technical Univ. Lodz, Div. of Polymer Physics, Lodz, POLAND.

In the last few years the request for inexpensive materials for use as efficient xerographic layers, photorefractive devices and large area solar cells has stimulated considerable research activities on photogeneration of charge carriers in soluble conjugated polymers. Various sensitizers have been used to increase the low intrinsic generation efficiencies in these materials. A new, attractive approach to long wavelength sensitization and enhancement of generation efficiencies is the use of dye coated semiconductor nanoparticles. [1] We present steady state photoconductivity experiments performed on solid films of inorganic/organic composites. The photoresponse of devices with different polymer hosts proof that an enhanced and spectrally broadened photogeneration of charge carriers requires electron transfer from the polymer to the dye. While for low nanoparticle concentrations photoaction spectra exhibit a pronounced peak at the absorption edge of the polymer, signatures due to the absorption of the Ru-dye are observed for high TiO₂ contents. Photocurrents and the shape of the photoaction spectra are only weakly affected by replacing anatase/brookite TiO₂ with rutile TiO₂. The I-V-characteristics of the composites indicate an enhanced injection of electrons from both electrodes into the dye coated nanoparticles and that percolation networks of nanoparticles are formed. Charge collection efficiencies exceeding 100% are observed and explained by photoconductivity gain phenomena. These effects might be particularly enhanced in the composite devices. Since transport of the two kinds of charge carriers occurs in different phases, reducing the probability for charge carrier recombination. [1] M. Kocher, T.K. D, E. Harth, U. Scherf, A. G, D. Neher, Appl. Phys. Lett. 72(5), (1998) 650 - 652

10:45 AM DD13.7
SYNTHESIS & CHARACTERIZATION OF OPTICALLY-ACTIVE LANTHANIDE-DOPED HYBRID INORGANIC-ORGANIC SYSTEMS. R.E. Taylor-Smith , K.M. Choi, Bell Laboratories, Lucent Technologies, Murray Hill, NJ.

The materials chemistry of sol-gel-derived inorganic-organic molecular composites offers significant potential for molecular-level systems design. One focus in this arena is the chemical design and microstructural engineering of optically-active systems. We report the generation of rare-earth-doped inorganic-organic hybrids, based on a bridged-polysilsesquioxane architecture. Derived from lanthanide precursors such as erbium isopropoxide, which we co-condense with the requisite silsesquioxane monomer, these systems exhibit significant optical activity. In experiments on hybrids doped with erbium, we conclusively demonstrate that the ⁴I_13/2 => ⁴I_15/2 transition results in strong fluorescence at wavelengths in the vicinity of 1540 nm, from stimulation with 488 nm radiation. We discuss materials-driven impacts of the bridged-polysilsesquioxane architecture on system complexities arising from the solution sol-gel route which would affect fluorescence efficiencies and luminescence levels, such as hydroxyl impurities and clustering-effects.

11:00 AM DD13.8
OPTICAL SPECTROSCOPY OF ORGANIC-INORGANIC PEROVSKITES. C.R. Kagan , D.B. Mitzi and K. Chondroudis, IBM T. J. Watson Research Center, Yorktown Heights, NY.

We report on the optical properties of self-organizing hybrid materials based on alternating anionic perovskite sheets and stereoregular, cationic organic layers. The inorganic sheets extend in 2D and behave like semiconductor quantum wells, having excitons with large binding energies and oscillator strengths. Choosing the chemistry of the perovskite sheet (for example, A₂MX₄ where A= organic cation, M= metal such as Pb or Sn, and X= anion such as Cl,Br, I) tunes the optical absorption and photoluminescence of the inorganic sheet through the visible. We correlate the structure and optical properties of the organic-inorganic hybrids as a function of temperature for both thin films and single crystals. Tailoring the electronic structure of both the organic and inorganic layers may be used to control the interaction between the layers of the hybrid and the color of its emission.

11:15 AM DD13.9
OPTICAL SENSING WITH SOLVATOCHROMIC DYES INCLUDED IN ZEOLITE HOSTS. Julia L. Meinershagen and Thomas Bein, Department of Chemistry, Purdue University, West Lafayette, IN.

The inclusion of Solvatochromic dyes in the crystalline cage system of zeolite hosts has been explored for the design of highly selective optical sensors. Approaches such as in situ synthesis, ion exchange as well as direct adsorption into zeolite hosts were demonstrated for dye encapsulation. Several solvatochromic dyes, showing different response mechanisms to their environment, were explored for sensing applications. Dramatic, reversible shifts in the absorbance and fluorescence spectra of the encapsulated dyes in the presence of various analytes were observed. For example, we demonstrate the inclusion synthesis of Nile Red in zeolites from 1-naphthol and 6-nitroso-3-diethylaminophenol (as a limiting reagent) in acidic environments. In siliceous faujasite, the stable hydrophobic dye/zeolite ensemble shows a hypsochromic shift of ca. 70 nm in the diffuse reflectance spectrum upon exposure to ethanol and acetone vapors at low pressures. Size exclusion was explored by using a more bulky molecule such as 2-4-di-tert-butylphenol. While a wavelength shift in solution is observed from the interaction of Nile Red with 2-4-di-tert-butylphenol, it does not respond when encapsulated in the zeolite. By restricting highly solvatochromic dyes into zeolite hosts, we demonstrate specificity towards various molecules, as well as size selectivity that can be applied in chemical sensing.

11:30 AM DD13.10
INORGANIC QUANTUM DOT - ORGANIC DENDRIMER NANOCOMPOSITE MATERIALS. Kelly Sooklal, Jinman Huang, Catherine J. Murphy , Univ of South Carolina, Dept of Chemistry and Biochemistry, Columbia, SC; Leo Hanus, Harry J. Ploehn, Univ of South Carolina, Dept of Chemical Engineering, Columbia, SC.

Semiconductor quantum dots are of great current interest for their optical properties. We have developed a method for preparing CdS quantum dots in commercially available PAMAM Starburst dendrimers. The resulting dots are exceptionally stable and emit brightly in the blue. The CdS quantum dots have optical signatures that suggest they are very small (20 Å, yet transmission electron microscopy and dynamic light scattering studies suggest that that the dots and dendrimers aggregate into nearly micron-scale flocs that are very soluble. Thin films are readily cast from such solutions, and the emission remains intact. The dot-dendrimer nanocomposites can be captured in a silica sol-gel matrix to yield a stable, bright blue-emitting glass. Compared to other stabilizing agents, the dendrimers protect the CdS quantum dots from coalescence into larger dots. Pre-aggregation of the dendrimers also influences the size and emission of the resulting CdS dots.

11:45 AM DD13.11
THERMOCHROMIC COMPOSITIONS BASED ON HYBRID ORGANOINORGANIC PVA COMPLEXES. T.G. Lazareva , E.P. Kalutskaja, Institute of General and Inorganic Chemistry of the National Academy of Sciences of Belarus, Minsk, BELARUS.

The possibility of forming the thermochrornic compositions based on hybrid hydrated organoinorganic complexes of polyvinyl alcohol (PVA) and the basic principles of their formation are discussed. The methods of IR spectroscopy as well as the differential and sorption methods have been adopted to study structural peculiarities or the complexes depending on the Co²⁺ concentration. A role of anions, with Cl ^-, NO₃^- taken as an example, in the complex formation is evaluated. The processes of hydration and the changes in the structure of the PVA - Co²⁺ complexes upon sorption are investigated. The basic information on the structure of PVA - Co²⁺ complexes is obtained, first of all, from an analysis of the absorption region of OH-groups in the IR spectra as well as absorption bands of the metal. A shift of the absorption region of the OH-groups toward a low-frequency region is noticed, new bands with maxima at 3160 cm^-1 and 500 cm^-1 are detected. A conclusion is made about formation of the PVA - Co²⁺ - Cl^- compound, in which a metal cation interacts with an oxygen atom of the OH-group via donor-acceptor bonds, while Cl^- anions participate in formation of stable hydrogen bonds with the OH-groups of PVA with respect to the oxygen atom. The possible schemes of complex formation are given. It is established that the complex formation leads to a decrease in the degree of crystallinity of the polymer matrix from 10 to 30 depending on a metal concentration, a decrease of the share of syndio-and heterotactic phases. Introduction of Co²⁺ ions into the PVA matrix causes the considerable enhancement of sorption of water molecules starting from 30 relative elasticity of water vapor upon sorption. In this case, if in the initial stages of hydration water molecules are bounded with the OH-groups of PVA, in the intermediate stages (>30 relative elasticity of water vapor) water molecules enter the coordination sphere of the cation by partially destructing the PVA - Co²⁺ bonds and forming large hydrated structures with the spectroscopic features typical for the spectra of aqueous solutions forming the O^...H^...O fragments. Reversibility of the sorption processes due to the sorption-desorption-sorption stages is also considered. The compositions are recommended as promising thermochromic materials.