Symposium OrganizersJoseph B. Tracy, North Carolina State University
Yadong Yin, University of California, Riverside
Nicole S. Zacharia, Texas Aamp;M University
Unyong Jeong, Yonsei University
Symposium Support Army Research Office
GG2: Fundamentals of Self-Assembly II
Tuesday PM, April 10, 2012
Moscone West, Level 3, Room 3011
2:30 AM - *GG2.1
From Nanomers to Nanopolymers
Eugenia Kumacheva 1 Kun Liu 2 Zhihong Nie 3 Michael Rubinstein 4
1University of Toronto Toronto Canada2University of Toronto Toronto Canada3University of Maryland College Park USA4University of North Carolina Chapel Hill USAShow Abstract
Organized arrays of inorganic nanoparticles (NPs) show electronic, optical, and magnetic properties that originate from the coupling of size- and shape-dependent properties of individual nanoparticles. Controllable and predictable organization of NPs in complex, hierarchical structures provides a route to the fabrication of new materials and functional devices. In my talk, I will present two new paradigms for the self-assembly of NPs. One of the approaches exploits a striking analogy between amphiphilic ABA triblock copolymers and polymer-tethered inorganic nanorods in structures with varying geometries and functions. The self-assembly is tunable and reversible, and it is achieved solely by changing the solvent quality for the constituent polymer or inorganic blocks. The self-assembly process is conveniently mapped by the phase-like diagrams. The second approach relies on the similarity between the self-assembly of inorganic NPs (nanomers) and reaction-controlled step-growth polymerization to produce â?onanopolymersâ?. This approach enables the prediction of the kinetics and statistics of NP self-assembly in 1D structures, and the aggregation number, polydispersity and "isomerism" of the self-assembled nanostructures, as well as hybrid â?ocopolymerâ? structures. We demonstrate the ability to control the optical properties of the self-assembled nanostructures. The proposed strategy provides a new route to the quantitatively predicted organization of NPs in supracolloidal assemblies.
GG3: Nanoparticle-Grafted Polymers
Tuesday PM, April 10, 2012
Moscone West, Level 3, Room 3011
3:00 AM - *GG3.1
Functional Polymer Coatings with Nanoparticles for Sensing and Catalysis
Manfred Stamm 1
1Leibniz Institute of Polymer Research Dresden Dresden GermanyShow Abstract
Functional polymer brushes may be used at surfaces for coatings with adaptive properties and in connection with inorganic nanoparticles can serve as responsive and versatile functional layers. A fairly robust way for the generation of such nanoscopic coatings is the attachment of polymer chains to the surface by covalent bonding. Nanoparticles are attached by adsorption or covalent binding at the end of the chains. At high grafting density a brush-like layer will be formed, and surface properties can be changed significantly while bulk properties are largely unchanged. Utilizing mixed polymer brushes the surface properties can be switched between different states /1/, and it is even possible to switch between ultra-hydrophobic and ultra-hydrophilic behavior /2/. Depending on solvent conditions, one or the other polymer chain occupies the surface layer and thus determines surface properties, which depend on the outermost surface layer. This effect can be used to control the location of nanoparticles at the top or inside the layer. Layers are characterized in different ways including contact angle measurements, x-ray-photo-electron-spectroscopy, ellipsometry, quartz-crystal-microbalance and scanning force microscopy. Depending on the degree of swelling of the brush layer, fluorescent nanoparticles attached to the polymer brush chains /3/ will be close to the surface or further away and may serve as a sensitive optical sensor for the degree of swelling. By surface enhanced Raman scattering a chemical sensing is achieved /4/. Similarly the hydrophobic nature of a mixed brush layer can be changed by pH, ion strength or temperature, which allows to control the adsorption of polyelectrolytes and protein molecules depending on the state of the brush /5, 6/. Similarly the catalytic activity of nanoparticles depends on the position in the layer which can be varied /7/. We acknowledge support by DFG/NSF and BMBF for this work. /1/ S. Minko, M. MÃ¼ller, D. Usov, A. Scholl, C. Froeck, M. Stamm, Phys. Rev. Let. 88 (2002) 35502; M.A. Cohen Stuart, W.T.S. Huck, J. Genzer, M. MÃ¼ller, C. Ober, M. Stamm, G. B. Sukhorukov, I. Szleifer, V. V. Tsukruk, M. Urban, F. Winnik, S. Zauscher, I. Luzinov, S. Minko, Nature Materials 9 (2010) 101 /2/ M. Motornov, S. Minko, K.-J. Eichhorn, M. Nitschke, F. Simon, M. Stamm, Langmuir, 19 (2003) 8077 /3/ L. Ionov, S. Sapra, A. Synytska, A. L. Rogaci, M. Stamm, S. Diez, Advanced Materials 18 (2006) 1453 /4/ S. Gupta, M. Agrawal, M. Conrad, N. Hutter, P. Olk, F. Simon, L. Eng, M. Stamm, R. Jordan, Advanced Functional Materials 20 (2010) 1756 /5/ O. Hoy, B. Zdyrko, R. Lupitskyy, R. Sheparovych, D. Aulich, J. Wang, E. Bittrich, K.-J. Eichhorn, P. Uhlmann, K. Hinrichs, M. MÃ¼ller, M. Stamm, S. Minko, I. Luzinov, Advanced Functional Materials 20 (2010) 2240 /6/ E. Bittrich, KB Rodenhausen, K.J Eichhorn, T. Hofmann, M. Schubert, M. Stamm, P. Uhlmann, Biointerphases 5 (2011) 159 /7/ M. KÃ¶nig, P. Uhlmann, M. Stamm, to be published
3:30 AM - GG3.2
Dispersion and Rheological Properties of Bimodal Brush Graft Nanofillers
Bharath Natarajan 1 Ying Li 1 Atri Rungta 2 Tony Neely 2 Brian Benicewicz 2 Linda Schadler 1
1Rensselaer Polytechnic Institute Troy USA2The University of South Carolina Columbia USAShow Abstract
The grafting of polymer chains onto high surface energy nanoparticles is a promising approach to compatibilizing filler-polymer interactions in polymer nanocomposites. The literature on this topic has, thus far, been primarily focused on the brush structure and dispersion morphology in homopolymer systems, which are comprised of fillers grafted with monomodal distributions of polymer chains. It is well established that the â?owettingâ? or penetration of these chains by a chemically identical matrix is dictated by a delicate balance between the gain in the translational entropy of mixing with brush chains and the loss of conformational entropy of the melt chains when stretching to mix with the grafted brush. Thus, even in the absence of excess enthalpic interaction, a nonzero entropic surface tension at the interface leads to the â?~autophobicâ?T dewetting of matrix chains. Dewetting could conceivably be alleviated by reduction of brush graft density (Ïf) or by increasing the brush to matrix molecular weight ratio. Yet, increasing the brush molecular weight reduces the maximum achievable core loading, which is undesirable in functional materials (optical, dielectric) in which higher particle loadings enable larger property enhancements. Decreasing the Ïf exposes the particle surface, leading to the self assembly of fillers into anisotropic string and sheet like morphologies. This self assembly arises due to the block-copolymer like phase separation of immiscible polymer and filler while being constrained by the covalent grafting of the polymer, and is strongly dictated by the attraction between unscreened particle cores. Using optimally high grafting density chains has been found effective in obtaining good dispersions by the screening of inter-core attraction. However, using high density chains causes the matrix to dewet. A logical step forward would be to employ a novel bimodal polymer brush with dense short chains that shield core-core attractions and a small number of long chains that entangle with the matrix to retain mechanical integrity. These brushes have been recently synthesized through a novel Consecutive Reversible Addition-Fragmentation Chain Transfer Polymerization technique. A systematic study of the rheological response and dispersion of bimodal (118 kg/mol, Ïf=0.05 ch/nm2 and 10 Kg/mol Ïf=0.18 ch/nm2) polystyrene (PS) graft 15nm Silica in a 100 Kg/mol matrix PS reveals a marked improvement in dispersion and modulus over monomodal fillers, which aggregate into sheets in this range of long brush Ïf and molecular weights. Additionally a â?~wetâ?T to â?~dryâ?T transition is observed with increasing matrix Mw to 190 Kg/mol. The hardness and elastic moduli of other wetting (40 kg/mol, Ïf=0.2 ch/nm2, 2 kg/mol, Ïf=0.26 ch/nm2 in 30 kg/mol matrix) and nonwetting (100 kg/mol, Ïf=0.2 ch/nm2, 25 kg/mol, Ïf=0.26 ch/nm2 in 100 kg/mol matrix) nanocomposite systems also show a remarkable improvement, superior to values suggested by the Halpin-Tsai mixing rule.
4:15 AM - *GG3.3
Organic-Inorganic Nanocomposites via Directly Grafting Conjugated Polymers onto Semiconducting Nanocrystals
Zhiqun Lin 1 Lei Zhao 1 Xinchang Pang 1
1Georgia Institute of Technology Atlanta USAShow Abstract
Nanocomposites of poly(3-hexylthiophene)-cadmium selenide (P3HT-CdSe) are synthesized, for the first time, by directly grafting vinyl terminated P3HT onto [(4-bromophenyl)methyl]dicotylphosphine oxide (DOPO-Br)-functionalized CdSe nanocrystals surfaces via a mild palladium-catalyzed Heck coupling, thereby dispensing with the need for ligand exchange chemistry. The resulting P3HT-CdSe nanocomposites possess a well-defined interface, thus significantly promoting the dispersion of CdSe within the P3HT matrix and facilitating the electronic interaction between these two components. The photophysical properties of nanocomposites are found to differ from the conventional composites in which P3HT and CdSe are physically mixed. Solid-state emission spectra of nanocomposites suggest the charge transfer from P3HT to CdSe. A faster decay in lifetime further confirms the occurrence of charge transfer in P3HT-CdSe nanocomposites.
4:45 AM - GG3.4
Colloidal Processing of Inorganic/Organic Hybrid Structures by Heteroaggregation
Anne Aimable 1 Fahouzi Belounis 1 Marguerite Bienia 1 Roxanna Chotard-Ghodsnia 1 Arnaud Videcoq 1 Fabrice Rossignol 1 Cecile Pagnoux 1
1Centre Europeacute;en de la Ceacute;ramique Limoges FranceShow Abstract
The use of nanoparticles in the field of ceramics has already led to great advances. One important issue is their processing through conventional forming processes; it remains difficult due to the high developed surfaces. Colloidal processing is an interesting way for ceramics, and opens a wide range of possibilities, e.g. through direct coagulation casting (DCC), or electrophoresis deposition (EPD). In recent years, our group has more particularly developed the heteroaggregation process, which is based on a controlled grain agglomeration and the coalescence of such agglomerates in dilute media. This mechanism is quite simple, depending on the particle surface interactions which are explained by the DLVO theory. However the control of the process when colloids of different natures and sizes are used opens interesting perspectives. At first heteroaggregation has been applied to a two-component system made up of alumina and silica. Experimental data from cryo-SEM and confocal observations could be perfectly modeled by Brownian Dynamics simulations. Then inorganic/organic hybrid materials were prepared: TiO2 and polystyrene (PS) latexes, as well as hydroxyapatite and polymetacrylate beads (PMMA). Heteroaggregation allowed shaping micrometric and millimetric ceramic spheres with a homogeneous distribution in terms of size and shape, leading to a homogeneous distribution of the porosity after calcination. Finally hybrid structures were processed from inorganic nanoparticles modified by a silane anchoring. Aminopropyltriethoxysilane was used to modify the zeta potential of silica from -40mV to +60mV, and interact with polystyrene (PS) beads with different sizes. Methylpropyltriethoxysilane (MPS) could be grafted at the surface of a boehmite nanometric powder. Emulsion polymerization of PS was then conducted to grow the organic phase directly from the modified surface. These polymer-grafted colloids were then processed by heteroaggregation to form hybrid structures with various organic contents.
GG4: Layer-by-Layer Assembly I
Tuesday PM, April 10, 2012
Moscone West, Level 3, Room 3011
5:00 AM - *GG4.1
Layer-by-Layer Assembled NanoComposites or How to Obtain Materials with ``Impossible'' Combinations and Record Properties
Nicholas A. Kotov 1
1University of Michigan Ann Arbor USAShow Abstract
Layer-by-layer assembly (LBL) is materials manufacturing technique that affords multiscale engineering of nanocomposite materials based on sequential adsorption of nanometer scale layers of polymers and inorganic colloids. LBL can resolve hard challenges of materials science related to mechanical, electrical, optical, and biological properties. One of them is the design of materials with hard-to-reach combinations of electrical and mechanical properties necessary for energy conversion and storage characteristics. In this presentation, the principles of property engineering of these materials will be described. The focus technological areas will be (1) Flexible solar cells and solid state light emission devices; (2) High capacity lithium batteries; and (3) Biomedical implants with energy storage requirements. Manufacturing of such composites in large scale will also be addressed. LBL films exhibit exceptional mechanical performance. This property becomes very essential in preparation of transparent conductors for flexible solar cells. One of the key hurdles on their mass utilization is replacement of expensive indium tin oxide coating, which also reveals deficient performance in bending, which is essential for flexible electronic devices. It will be demonstrated that the LBL films made from carbon nanotubes and appropriate polymers reveal cumulative figure of merit taking into account both electrical and mechanical performance higher than standard ITO glass. Surface conductivity of the coatings was as low as 80 Ohm/square. Mechanical performance is essential for lithium ion batteries which is the key for attaining safety parameters. They are considered to be the main challenge for battery technologies in automotive and solar energy industries. It will be demonstrated that LBL films can achieve the combination of several characteristics enabling the new type of flexible Li+ batteries. Biomedical implants must have many parameters similar to those needed in energy conversion with additional requirements for biocompatibility and biodegradability. LBL composites can satisfy all these stringent set of conditions. Preparation and functionality of a new type of implantable electrodes using LBL multilayers from carbon nanotubes and other materials will be demonstrated. Relevant References. 1. Zhu, Jian et al, J. Am. Chem. Soc. 2011, 133 (19), 7450â?"7460 2. Andres, Christine. M.; Kotov, Nicholas A. J. Am. Chem. Soc., 2010, 132(41), 14496-14502 3. Shim, Bong Sup, et al., ACS Nano, 2009, 3 (7), 1711â?"1722. 4. Podsiadlo Paul., et al , Science, 2007,318, 80-83. 5. Mamedov, Arif. et al. Nature Materials, 2002, 1 190-194; 6. Tang, Zhiyong.; et al. Nature Materials, 2003, 2, 6, 413-418.
5:30 AM - *GG4.2
Nucleophilic Substitution Reaction-induced Layer-by-layer Assembly for Functional Nanocomposite Films with Optical, Magnetic and Electronic Properties
Jinhan Cho 1 Younghoon Kim 1 Miseon Yoon 1
1Korea University Seoul Republic of KoreaShow Abstract
We introduce a facile and robust approach for the preparation of functional nanocomposite multilayers, which allows the highly enhanced optical, magnetic and electronic properties as well as the dense and homogeneous adsorption of nanoparticles. By employing 2-bromo-2-methylpropionic acid (BMPA)-stabilized nanoparticles (BMPA-NPs) with bromo groups in toluene and highly branched poly(amidoamine) dendrimer (PAMA) with amino groups in ethanol, PAMA/BMPA-NP multilayers were prepared by nucleophilic substitution reaction in nonpolar solvent. The resulting superparamagnetic multilayers displayed highly improved opical and magnetic properties in comparison with those of multilayers based on water-dispersible NPs. Furthermore, we demonstrate that these functional multilayers using nucleophilic substitution reactions can be used as nonvolatile resistive switching memory (NRSM) devices.
GG5: Poster Session
Tuesday PM, April 10, 2012
Moscone West, Level 1, Exhibit Hall
6:00 AM - GG5.10
``Grafting To'' a Click Approach to Matrix-free Synthesis of Hairy Nanoparticles
Kimberly E Kern 1 2 Hilmar Koerner 1 2 Scott P Fillery 1 Lawrence F Drummy 1 2 Folusho T Oyerokun 1 2 Richard A Vaia 1
1Air Force Research Laboratory Wright-Patterson AFB USA2UES, Inc. Dayton USAShow Abstract
Hairy nanoparticles are becoming increasingly important for dielectric, shape memory, and metamaterial applications; in large part due to improved dispersion and enhanced morphological control compared to traditional filler surface modifiers and composite blending approaches. Optimizing the properties of hairy particles depends upon the ability to control the composition and structure of the organic corona, including grafting density, corona thickness, and polymer composition. The corona may be formed by attaching end funtionalized polymers to a reactive nanoparticle core (â?ografting toâ?) or growing the polymer from an initiator functionalized core (â?ografting fromâ?). While â?ografting fromâ? enables high graft density, it is challenging to create multi-component coronas of precisely control polymer molecular weight, where gelling of the reaction medium often occurs at high molecular weights. Here in, a systematic array of hairy nanoparticles, including corona composition, graft density, and molecular weight, is demonstrated via a â?ografting toâ? methodology based on silane coupling and click chemistry. Chromatography is utilized to monitor grafting kinetics, content of unattached chains, and stability of the hairy nanoparticles to extreme shear and temperature processing. The predictability of the â?ografting toâ? process is verified by comparison to recent theories of adsorption of end-functionalized polymers onto curved interfaces. The impact of corona structure, including thickness, grafting density, and molecular weight, on physical properties of assemblies of hairy nanoparticles, in the absence of unattached matrix chains, will be discussed.
6:00 AM - GG5.12
Optoelectronic Nanoparticles and Nanostructures with Self-assembled Templates of Polymeric Micelles and Thin Films
Jeong-Hee Kim 1 Jin-Hyung Kim 1 Byeong-Hyeok Sohn 1
1Seoul National University Seoul Republic of KoreaShow Abstract
Block copolymers composed of two or more chemically different polymers spontaneously self-assemble into periodic nanostructures, the size and morphology of which can be easily tuned by the molecular weight and composition of copolymers. In a selective solvent that dissolves only one of the blocks, diblock copolymers self-associate into micelles with coronas of the soluble block and cores of the insoluble block. Diblock copolymer micelles containing precursors of nanoparticles can be applied to synthesize various metal and semiconducting nanoparticles. Thin films of block copolymers, which form self-assembled cylindrical or lamella nanodomains, can also be utilized as nanotemplates for fabrication of periodic nanostructures of a variety of materials in a controlled manner such as metallic patterns of nanolines. In this study, we synthesized fluorescent silica nanoparticles templated by spherical diblock copolymer micelles. Precursors of silica nanoparticles with organic fluophopohore-conjugated silane were selectively incorporated into the core block of copolymer micelles. Fluorophore-doped silica nanoparticles in a narrow size distribution were synthesized by acid-catalyzed sol-gel process and were characterized by TEM and PL measurements. By spin coating of fluorescent silica nanoparticles, we fabricated arrays of fluorescent silica nanoparticles. We also fabricated nanostructured inorganic semiconductors using self-assembled block copolymer thin films as templates. A nanogroove pattern was obtained by selective removal of one of the blocks of perpendicularly oriented lamellae of copolymers in thin films. Titania nanostructures templated by the nanogroove were successfully fabricated by the liquid ALD method. FE-SEM and XPS measurements were carried out to characterize titania nanostructures, which can be applied to electrodes of photovoltaic cells.
6:00 AM - GG5.13
Fabrication of Gold Ring Arrays from Block Copolymer Templates via a Simple Modification of Surface Energy
Heesook Cho 1 Soojin Park 1
1UNIST Ulsan Republic of KoreaShow Abstract
Metal nanoring arrays have attracted increasing attention due to their potential applications, like unique magnetic and optical properties. Indeed, there have been extensive efforts to fabricate the nanoring arrays onto metallic, semi-metallic, and glass substrates, by employing various fabrication techniques including photolithography, electron beam lithography, template-based methods, colloidal lithography, capillary lithography, and self-assembly of block copolymers. In particular, block copolymer (BCP) self-assembly, which is tunable in dimensions and morphologies depending on the molecular weight and chemical composition, has been shown to be a simple, flexible and powerful strategy to fabricate nanoring arrays in a large area with a low cost. The self-assembled BCP thin films can be used as templates or scaffolds to fabricate well-defined nanoring arrays. We present here a simple and high-throughput approach for fabricating metal nanodot, nanoring, and corpuscle arrays using polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP) micellar templates with a control of surface energy. The PS-b-P2VP copolymers dissolved in o-xylene are formed spherical micelles consisting of PS corona and P2VP core. When the copolymer solutions were spin-coated onto a PS-modified silicon substrate, the micellar film consisted of a thicker PS shell than that of micelles prepared onto a normal silicon substrate, due to a favorable interaction between the PS-brush layer and the PS corona in the micelles. Subsequently, when the BCP thin films were immersed in Au precursor solution, the Au salts migrated to the interface between PS corona and P2VP core to make hollow Au structures. By exposing it to oxygen plasma, the Au nanoring arrays were obtained without changing the separation distance of the original BCP micellar films. As the loading time of Au precursors increased, the final Au morphologies changed to an Au ring with a thicker wall and a corpuscle-like structure. This approach can be extended to other metal oxide nanoring arrays, like CuO, Fe2O3, and ZnO. In contrast, when micellar films spin-coated onto a normal silicon surface were used as templates, only Au dotted arrays were obtained. A simple tuning of surface energy enabled us to control the morphologies of the Au nanostructures.
6:00 AM - GG5.15
Evaluation of Optical and Electrical Properties of CuS/Polyaniline Nanocomposite Using a Soft Chemical Synthesis Route
Anamika Dutta 1 Swapan K Dolui 1
1Tezpur University Tezpur IndiaShow Abstract
This study refers to a soft chemical synthesis route for nanocomposite based on CuS nanoparticles and polyaniline (PANI), and the evaluation of electrical and optical properties. The nanocomposite is characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), ultraviolet-visible absorption spectra (UV-vis) and photoluminescence spectra (PL). SEM and TEM images reveal the complex architecture of CuS/PANI nanocomposite. I-V characteristics of PANI and CuS/PANI were studied using Keithley 2400 source meter at room temperature in the frequency range of 102-106 Hz. Both the compounds exhibited similar semiconducting behaviour with respect to applied voltage . The DC electrical conductivity of PANI and CuS/PANI composite was measured using four probe technique and discussed. This synthetic route opens a new dimension to get nanomaterials with complex architectures with the possibilities for future technological applications. References:  Dey, A.; De, S.; De, A.; De, S. K. Characterization and dielectric properties of polyaniline-TiO2 nanocomposites, Nanotechnology 15 (2004) 1277-1283.
6:00 AM - GG5.16
Simultaneous Enhancement of Photoluminescence and Raman Spectroscopy of Ag/Polydiacetylene Core-shell Single Nanoparticle: Plasmonic Resonance Coupling Effect
Chunzhi Cui 1 Dong Hyuk Park 1 Gil Sun Lee 1 Dong June Ahn 1
1Korea University Seoul Republic of KoreaShow Abstract
We experimentally demonstrated the surface plasmon coupled enhancement both in photoluminescence (PL) and Raman spectroscopy from core-shell hybrid single nanoparticle (NP) consisting of Ag core and polydiacetylene (PDA) shell. We fabricated a core-shell NP in deionized (DI) water solution through reprecipitation and hydrothermal method. We used a high-resolution laser confocal microscope (LCM) combined with atomic force microscope (AFM) to obtain the LCM PL and Raman spectroscopy along with the nanoscale topographic information from individual single NP. We simultaneously observed a significant enhancement of the PL and Raman signals from the core-shell NP by the factor of about 55 and 100, respectively, compared with the PDA single NP. This indicates the excitation of surface plasmon due to the existence of Ag in core-shell NP inducing strong electromagnetic field near Ag/PDA interface. We were also able to analyze statistically the enhancement rates of surface plasmon coupled PL and Raman signals from LCM PL and Raman mapping images from multiple NPs. This new synthetic process provides a simple way of fabricating metal/conjugated polymer hybrid nanostructures being potentially important in high performance optoelectronic and/or biochemical applications.
6:00 AM - GG5.18
Highly Refractive Poly(2-ethyl-2-oxazoline) Coatings Incorporating TiO2 Nanoparticles
Annalisa Colombo 1 Francesco Tassone 2 John K Delaney 3 E Rene de La Rie 3 Domenico Salerno 4 Michael Palmer 3 Roberto Simonutti 1
1University of Milano Bicocca Milan Italy2IIT@POLIMI Milan Italy3National Gallery of Art Washington USA4University of Milano-Bicocca Monza ItalyShow Abstract
In recent years a few examples of nanocomposites with optimized optical properties have been reported. The research has been focused mainly on the following goals: luminescence, change (increase) of the refractive index (RI), UV absorption. In particular high RI polymer nanocomposites can be obtained by incorporation of inorganic building blocks with high RI (such as InP, PbS, TiO2, ZrO2, or ZnS) into organic matrices on the nanoscale. Concerning polymers, which are the embedding matrix for the inorganic nanoparticles, poly(meth)acrylates represent the most studied class since their feature high intrinsic optical clarity -especially in the case of polymethylmethacrylate- and the possibility to modulate the physico-chemical properties by simply varying the nature of the side chains. Quite rarely water soluble polymers are used, although the hydrophilicity of the macromolecular chains can, in principle, avoid aggregation of the nanoparticles, especially in the case of oxides that present hydrophilic surfaces. Here we report for the first time the preparation and optical characterization of nanocomposite films made of TiO2 dispersed in the water soluble polymer poly(2-ethyl-2-oxazoline). This polymer was chosen because of its solubility in water, lack of toxicity and stability. It features several recognized applications as an adhesive and as a coating. Nanocomposite films characterized by three different concentrations of TiO2 nanoparticles (20 nm average radius) in the polymeric matrix (16%, 28% and 44% w/w) were obtained. Optical characterization using UV-visible spectroscopy has shown that the films feature significant UV absorption below visible wavelengths and good transparency for visible wavelengths. Moreover, the highly TiO2 loaded films feature a high-refractive index of up to 1.67. The nanocomposites surface was studied by AFM, showing good coverage of extruding nanoparticles by the soft polymer. The roughness of the surface related to the high fraction of nanoparticles is not having a negative impact on the optical quality of the films which remains excellent, as clearly assessed by specific optical measurements of specular gloss and distinctness-of-image (DOI).
6:00 AM - GG5.19
Novel Hybrid Integration for Unconventional Laser Device Materials; Acoustically Coupled Photorefraction
Kyung M. Choi 1
1University of California Irvine USAShow Abstract
Doped organic/inorganic hybrid glasses with a molecular alignment were molecularly designed for unconventional optical device materials based on the periodicity at the nano-scales; molecular-level hybridization often results in new properties, which individual components didnâ?Tt have. TEM images of the hybrid glass with the molecular arrangement reveal a novel nano-structured fringe pattern. The hybrid glass exhibits an unconventional optical property, photorefraction modulated by acoustic waves. The most striking observation from the hybrid glass is acoustically coupled photorefraction. Additionally, the photorefraction that we report is in a centrosymetric material and does not require the application of static electric fields or polling during material synthesis. While both photorefractive and acoustic grating can be separately demonstrated in different materials, we do not know of examples in which the two effects are coupled. Implicit in such behavior is fast response photorefraction, which is ascribed to the density-controlled mobility of electrons trapped in aligned nano-domains of the hybrid sol-gel hosts. Applications, such as light modulators that rely on electro-acoustic-optical response, acousto-optics, and dynamic holography, are suggested.
6:00 AM - GG5.2
Electrospun Nylon-graphene Nanocomposites Synthesis and Microstructure
Loyda Albantilde;il-Sanchez 1 Angel Romo-Uribe 1 Araceli Flores 2 Rodolfo Cruz-Silva 3
1Universidad Nac A de Mexico Cuernavaca Mexico2C.S.I.C. Madris Spain3Universidad A Edo Morelos Madris MexicoShow Abstract
There has been much interest in the last few years on materials reinforced with nanometer scale particles. These so-called nanocomposites can exhibit hybrid properties derived from its components. One of the most promising nanocomposites is that based on polymers reinforced with single-layered carbon sheets named graphene. The reason is that graphene can significantly improve the physical properties of the polymeric material once it is completely dispersed in the matrix. In this work nylon/graphene nanocomposites were prepared starting from the synthesis of graphite oxide (GO). Direct oxidation of graphite powder was utilized to produce GO. That is, the oxidation reaction produced graphite layers with functional groups containing oxygen. The aim was to increase the polarity of GO to enable a good dispersion in polar solvents. Then, nylon/graphene nanocomposites were prepared by reducing GO in the presence of nylon. Finally, non-woven membranes, with nanometer sized filaments, of nylon/graphene were electrospun. The morphology and microstructure of the nanocomposites was investigated via electron microscopy and X-ray diffraction
6:00 AM - GG5.20
Polymer-nanocrystal Composites for Electrochromic Devices
Evan L Runnerstrom 1 3 Guillermo Garcia 2 3 Raffaella Buonsanti 3 Anna Llordes 3 Teresa E Pick 3 Brett A Helms 3 Delia J Milliron 3
1University of California Berkeley USA2University of California Berkeley USA3Lawrence Berkeley National Laboratory Berkeley USAShow Abstract
Recent work in our group has yielded a new type of electrochromic device based on the near-infrared (NIR) modulation of localized surface plasmon resonance (LSPR) in metal oxide nanocrystals (Garcia et al, Nano Lett., 2011). In order to develop a solid state device, this work utilizes ITO nanocrystals as an active, switchable component in a polymer electrolyte-nanocrystal composite. ITO nanocrystals were prepared by colloidal chemistry and the nanocrystal surface functionalization was modified to achieve favorable nanocrystal-polymer interactions. Homogeneous solutions containing polymer, ITO nanocrystals, and lithium salt were then prepared and deposited by a variety of methods. Characterization revealed that the ITO nanocrystals form a complete, connected electrode within a polymer electrolyte matrix. Electrochemical experiments also showed that the nanocomposite displays switching behavior. The result is a polymer-nanocrystal composite thin film with coupled properties; nanocrystals conduct electrons and serve as an electrochromic cathode while the polymer matrix stores and conducts ions.
6:00 AM - GG5.21
In situ Synthesis of Transparent Ln-doped ZnO Particle/Organic Hybrid with Malleability
Masahiro Kachi 1 Masao Ichida 2 Tomoo Wada 2 Hiroaki Ando 2 Wataru Sakamoto 1 Toshinobu Yogo 1
1Nagoya University Nagoya Japan2Konan Univ. Kobe JapanShow Abstract
Functional inorganic nanoparticle/organic hybrid materials have attracted attentions because of their beneficial properties of each phase. Zinc oxide is an n-type semiconductor with wurtzite structure and its nanoparticle is used for luminescent materials and photocatalysts. The authors reported the synthesis of Fe-doped ZnO particle/organic hybrid from metal-organics . ZnO is an appropriate host oxide for many visible photoluminescence (PL) centers. ZnO nanoparticles doped with rare-earth ions are expected to be novel optical materials because of their sharp and intense optical emission spectra. This paper describes the synthesis of transparent Ln-doped ZnO particle/organic hybrid with malleability. Zinc-organic and rare earth-organic dissolved in ethanol were hydrolyzed and polymerized under controlled conditions. The hybrid was analyzed by FT-IR, DTA-TG, powder XRD, UV-visible and luminescence spectroscopy. The crystallite size increased with increasing hydrolysis time. The size of ZnO particles dispersed in the hybrid was controlled by selecting the hydrolysis conditions. Self-standing hybrid films were fabricated from the hybrid solution by casting. The hybrid film had a high transparency because of nano-sized ZnO particles undergo no scattering at particle-organic interfaces. The hybrid film showed an absorption edge at 370 nm. Ln-doped ZnO particle/organic hybrids were confirmed to generate characteristic emissions of Eu or Er ion. Ln-doped ZnO particle/organic hybrid has a potential of applications in malleable luminescence materials. 1. T. Yogo, T. Nakafuku, W. Sakamoto and S. Hirano, J. Mater. Res., 20, 1475(2005).
6:00 AM - GG5.22
Nanocomposite of Polymer and Fluorescent Silica Nanoparticles as a Color-converter for White Light-emitting Diode Application
Hak Sung Jung 1 Shin-Woo Ha 1 Inhyung Lee 2 Chulsoo Yoon 2 Jin-Kyu Lee 1
1Seoul National University Seoul Republic of Korea2Samsung Electronics Yongin Republic of KoreaShow Abstract
Trialkoxysilyl terminal groups could be directly introduced into yellow-fluorescent organic dye molecule (N-alkyl-4-alkylamino-1,8-naphthalimide, NAAN) by the consecutive reactions of allylation and hydrosilation from 4-sulfo-1,8-naphthalic anhydride potassium salt. This derivatized dye molecule was successfully incorporated into silica nanoparticles by co-condensation with TEOS in basic ethanol solution. The emission characteristics from the SiO2(NAAN) nanoparticles were very similar to the parent dye molecule, showing a very bright yellowish green photoluminescence. SiO2(NAAN) nanoparticles were mixed with silicone polymer to apply onto LED chip, and the whole LED chip was dried at 25 Â°C to remove the solvent and then cured to form a homogeneously dispersed hybrid composite. Details on characterization and development of new yellow nanophosphor material will be discussed.
6:00 AM - GG5.3
Probing Damaged Substrates Using ``Repair and Go''
Katrina Kratz 1 Thomas Russell 1 Alfred Crosby 1 Anna Balazs 2 Todd Emrick 1
1University of Massachusetts Amherst USA2University of Pittsburgh Pittsburgh USAShow Abstract
Simple and general methods are needed for the localized delivery of nanoscale materials to surfaces and within bulk materials. Encapsulation offers one method for achieving such delivery objectives, by protecting the nanoscale contents until the desired point of release. Here is the experimental realization of an efficient process of localized delivery, termed repair-and-go, which to-date has remained a theoretical challenge. We show that nanoparticle-containing microcapsules probe a damaged (cracked) surface, and identify its imperfections by depositing the nanoparticles into the cracks. This selective delivery is performed using a phosphorylcholine-polymer surfactant for stabilizing oil droplets in water, where CdSe quantum dots are initially encased in the oil phase. The encased nanoparticles escape into the cracked regions of a SiO2-coated poly(dimethylsiloxane) substrate as the droplets traverse the surface. While the â?orepairâ? aspect of repair-and-go is demonstrated as a selective deposition of nanoparticles, the concept has implications for modifying the mechanical, optical, and/or electronic properties of a wide range of materials. This probing, identification, and delivery motif borrows from repair techniques of cellular biology (i.e., the action of leukocytes), replacing complex biological signaling with simple surface energy recognition.
6:00 AM - GG5.4
Patterning Inorganic Materials through Viscoelastic Flow and Phase Separation
Minwoo Park 1 Bongsoo Kim 1 Minkwan Shin 1 Jaeyoon Park 1 Unyong Jeong 1
1Yonsei University Seoul Republic of KoreaShow Abstract
In spite of many years of research, there is still a strong need to develop a simple and versatile technique for patterning a rich variety of materials over large areas. Here we demonstrate a novel soft lithography technique that is applicable to metals and semiconductors. The technique is based on self-organization, involving viscoelastic flow of a polymer melt from a pre-formed pattern and phase separation between the polymer melt and the material to be patterned. Hard materials with a melting point higher than the annealing temperature are concentrated in the recessed regions of the polymer pattern to generate continuous but porous structures that are advantageous for the production of composites with interpenetrating network (IPN) of the materials. Soft materials with a melting point lower or comparable to the annealing temperature form a sharp liquid-liquid interface with the polymer melt and evolve into solid structures. We have demonstrated fabrication of complex patterns from diverse inorganic materials with sub-micrometer feature sizes.
6:00 AM - GG5.5
Asymmetric Position-dependent Polymer Patterns Due to Thermal Deformation of an Elastomer Stamp in Capillary Force Lithography
Unyong Jeong 1 Kim Bongsoo 1 Minwoo Park 1
1Yonsei University Seoul Republic of KoreaShow Abstract
During the Capillary force lithography (CFL) process, It is often observed that polymer patterns are not symmetric, and position-dependent even in one sample. The disadvantage has not been explained successfully so far. This paper reveals that the position-dependent polymer pattern is mainly caused by the thermal expansion and contraction of the elastomer stamp during tempertaure changes in the CFL process. The stamp expands on a polymer liquid on heating and accumulating the polymer liquid at one side-wall of each pattern of the stamp. In the other hands, the stamp contracts back to the initial position, accumulating the polymer liquid at the opposite wall of pattern of the stamp. For crystalline polymers, the final morphology was determined by the heating temperature, that is, the degree of expansion. The position-dependence of the morphology was enlarged as the annealing temperature was increased. For amorphous polymers, the final morphology was sensitive to cooling rate. Fast cooling led to a frozen morphology generated at the high annealing temperature, while slow cooling produced an opposite morphology from the one at the heating. The experimental results were theoretically explained by the shear stress exerted in the polymer layer and elastomer stamp. In the conclusion, we added our suggestions to avoid the non-uniform pattern in the CFL process.
6:00 AM - GG5.6
Continuous Production of Functionalized Polymer Particles through the Phase Separation in Polymer Blend Films
ChooJin Park 1 BongSoo Kim 1 Unyong Jeong 1
1Yonsei University Seoul Republic of KoreaShow Abstract
A continuous prepartion of spherical or hemispherical polymer particles simply utilizing the phase separation in polymer blend films during the thin coating process. We took an advantage of the strong phase separation between a water soluble crystalline polymer as a matrix and hydrophobic polymers as minor components. We demonstrated the prepartion of water-soluble polystyrene (PS) particles, nitrilotriacetic acid (NTA)-functionalized PS particles for protein separation, and semiconducting poly(3-hexylthiophene) (P3HT) particles. The sizes of the particles could be controlled by adjusting the film thickness and weight fraction of the minor component polymers in the blend film. It provides a simple facile way to prepare polymer particles in a continous process.
6:00 AM - GG5.7
Transformation of Colloidal Nanocrystals on Graphene Oxide
Chaewon Pak 1 Doh C. Lee 1
1KAIST Daejeon Republic of KoreaShow Abstract
2-Dimensional (2-D) dispersion of semiconductor nanocrystals on a conductive template provides powerful implications for efficient transport of photoinduced charge carriers to targeting electrodes or reaction sites. Graphene, a highly conductive one-atom thick carbon sheet, is a suitable substrate in collecting the photocharges. However, challenges remain as dispersion of colloidal nanocrystals on a graphene leads to flocculation instead of uniform deposition. In this study, we used graphene oxide (GO) as a template. GO has several oxygen-containing functional groups, such as carboxylic, epoxide, hydroxyl, and ketonic moieties, on its surface. These functional groups can serve as an anchor to hold nanocrystals on its surface in a uniform 2-D dispersion. For example, we exchanged surface functional groups on CdSe nanocrystals so the nanocrystals can disperse on the 2-D GO layer. Interestingly, when we mix CdSe nanocrystals with GO in aqueous solution for 12 h, the nanocrystals undergo considerable size increase (from 3.5 nm to 500 nm) and crystalline transformation (from wurtzite CdSe to amorphous Se). The formation of amorphous Se globules indicates that GO promotes the cleavage of Cd-Se bonding and turns the structure in to Se. By tuning acidity of the bulk solution, we can minimize the undesirable transformation. Other nanocrystals, e.g., PbSe, CoPt3, and Co, were also blended with GO and we monitored their compositional and structural deformation. The set of experiments confirm that local acidity near the graphene oxide surface plays a critical role in the cleavage of the bonding and photogenerated charge carriers trapped in the functional groups of GO surface affect the crystalline deformation and transformation. We identified reaction conditions, pH or concentration, that allow nanocrystals to deposit on GO surface in uniform 2-D dispersion.
6:00 AM - GG5.9
Synthesis and Characterization of Polyimide-SiO2 Nanocomposites by Surface Modification of SiO2
Young-Jae Kim 1 Jin-Kyu Lee 1
1Seoul National University Seoul Republic of KoreaShow Abstract
Polyimide-SiO2. nanocomposites were successfully prepared by surface modification of silica nanoparticles with a ligand that has a structure similar to that of polymer repeating units. The modified silica nanoparticles in poly(amic acid) solution were subject to thermal imidization to obtain polyimide-SiO2. nanocomposite films. TEM analysis show that no significant aggregation in all polyimide-SiO2. nanocomposite films having up to 30 wt% of silica nanoparticles. The content effect of silica nanoparticles on the optical, thermal and mechanical properties was studied by UV-Vis spectrometer, thermal gravimetric analysis (TGA), thermal mechanical analysis (TMA) and dynamic mechanical analysis (DMA). Improved mechanical and thermal properties in polyimide-SiO2. nanocomposite films and relationship between those properties with silica contents will be discussed in detail.
GG1: Fundamentals of Self-Assembly I
Tuesday AM, April 10, 2012
Moscone West, Level 3, Room 3011
9:30 AM - *GG1.1
Polymer Capsules for Repair-and-Go
Todd Emrick 1
1University of Massachusetts Amherst Amherst USAShow Abstract
In repair-and-go, a flexible microcapsule filled with a solution of nanoparticles probes an imperfection-riddled substrate as it rolls over the substrate surface. The microcapsules are too large to be fully engulfed by the surface imperfections (cracks), but the flexibility of the capsule wall allows the capsules to interact with the crack, providing an opportunity for nanoparticle release. The thin capsule wall (~1 nanoparticle diameter thickness) allows the particles to escape into the cracks, driven in part by favorable interactions between the nanoparticle ligands and the cracked surface (i.e., hydrophobic-hydrophobic interactions). This probing, identification, and delivery motif borrows from repair techniques of cellular biology (i.e., the action of leukocytes), replacing complex biological signaling with simple surface energy recognition. The size selectivity and encapsulation aspect of repair-and-go resembles the action of liposomal systems in nanotherapeutics, which distinguish healthy vs. diseased (i.e., cancer) tissue based on vascular size and biological recognition events. In this work, such biological interactions are replaced with surface energies that dictate the potential for experimental implementation of the repair-and-go concept We describe an experimental realization of the repair-and-go concept, previously underpinned by theory and computation,9,10 using a cracked PDMS substrate and CdSe nanoparticles encapsulated in a phosphorylcholine-polymer surfactant stabilized oil droplets. The droplets probe the surface, are interrupted by imperfections in the surface, release their contents into the cracks, and exit the system as intact structures. The technique offers a very simple and unique method for preserving valuable cargo by encapsulation, and maximizing delivery efficiency to specific areas. While the â?orepairâ? aspect of repair-and-go is demonstrated here as a selective deposition of nanoparticles, the concept has implications for modifying the mechanical, optical, and/or electronic properties of a wide range of materials.
10:00 AM - GG1.2
Programmable Self-assembly and Rigidity of Solids
Alexei Tkachenko 1
1Brookhaven National Laboratory Upton USAShow Abstract
By decorating colloids and nanoparticles with various biomolecules, one can introduce highly selective key-lock interactions between them. This leads to a new class of systems and problems in soft condensed matter physics. I will present two theoretical problems dealing with self-assembly of DNA-functionalized nanoparticles. The first one deals with the inverse problem in self assembly, i.e. programming an arbitrary desired nanostructure. We proposed a hierarchical approach which involves self-assembly of particular building blocks which in turn would assemble into the target structure. We predict a set of conditions under which the scheme is expected to be essentially error free. The second problem deals with self assembly in binary system of DNA-functionalized colloids. Jointly with D. Frenkel group at Cambridge, we studied its phase behavior by combination of MC simulations analytical modeling. Interestingly, in both studies indicate a surprising connection to the fundamentally important problem of rigidity percolation in solids. In particular, one of the most important condition for robust self-assembly of a programmed structure is reduced to that coordination number of the connection network must exceed certain critical value above which the structure behaves as a regular elastic solid. In the other project, the thermodynamic solid-to-liquid transition correlates remarkably well with loss of rigidity of the crystalline phase (the so-called isostatic point). Acknowledgement: This research carried out at the CFN, Brookhaven National Laboratory, which is supported by the US DOE, Office of BES, under Contract No. DE-AC02-98CH10886.
10:15 AM - GG1.3
Controlled Assembly at Nanocrystal-polymer Interface: A General Method for Hollow Colloidal Nanocrystal Clusters
Zhenda Lu 1 Yadong Yin 1
1University of California, Riverside Riverside USAShow Abstract
We propose a general strategy for the fabrication of novel hollow colloidal nanocrystal clusters (HCNCs). Briefly, uniform nanocrystals and hydrophobic polymers are confined in an oil droplet in the oil-in-water emulsion system. Upon the evaporation of the low boiling point oil, the nanocrystals were expelled by the polymer as its concentration increased in the oil droplet and accumulated on the surface of polymers to form monolayer and multilayer assembly. The number of nanocrystal layers depends on the original nanocrystal/polymer ratio in the oil droplet. The size and morphology of assemblies can be conveniently tuned by controlling the size of nanocrystals, the chemical nature of protection ligands on nanocrystals and the type of polymers. Later, the nanocrystal/polymer composites are coated with a silica layer to enhance the stability and make them ready for post-modification. The stable, clean and well-dispersed hollow colloidal nanocrystal clusters can be finally fabricated by removing the polymers after calcination. By coating a layer of silica before calcination and removing it afterwards through chemical etching, we have been able to prevent the clusters from aggregating during heating, make the cluster surface hydrophilic and negatively charged, and eventually enhance the dispersibility of the clusters in aqueous solution. Such assembly approach will provide the research community a highly versatile, configurable, and reproducible process to prepare various hollow multifunctional structures.
10:30 AM - GG1.4
Supercritical Hydrothermal Synthesis for Super Hybrid Nanomaterials
Tadafumi Adschiri 1 Seiichi Takami 2 Tomohiro Arai 3 Kasumi Ishikawa 3 Masataka Ueda 3 Masatada Ueno 3 Hidenori Oshima 3 Takayuki Nakagawa 3 Kenji Fukushima 3 Shigeyuki Maeda Maeda 3 Kenji Miyata 3 Takehiro Morishita 3 Toshitaka Yamagata 3
1Tohoku University Sendai Japan2Tohoku University Sendai Japan3Japan Chemical Innovation Institute Tokyo JapanShow Abstract
Variety of materials have been developed so far, including ceramics, metals and polymers, but recent needs in the industries are of multi-functions of ceramics/metals and polymers. So far, variety of composite materials has been developed, but in many cases trade-off of the functions are of important issues: For example, workability is reduced due to the significant increase of viscosity, and transparency of the polymer is sacrificed. For overcoming the problem of trade-off, organic functionalization of inorganic nanoparticles is required to have higher affinity between nanoparticles (NPs) and polymers. The organic modification, NPs should be dispersed in an organic solvent with high concentration, which is difficult. There are significant needs in the industries for multi-functional materials. We proposed a new method to synthesize organic modified NPs in supercritical water, for the new functional materials. Since the organic molecules and metal salt aqueous solutions are miscible under the supercritical state, and water molecule works as an acid/base catalyst for the reactions, organic-inorganic conjugate nanoparticles can be synthesized under the condition. The hybrid NPs show high affinity with the organic solvent or the polymer matrix, which leads to fabricate the organic inorganic hybrid nanomaterials with the trade-off function (super hybrid nanomaterials). For power devices and semiconductor tips, the size is reduced while the power is increased, and thus the power density is increased drastically. How to release the heat from the devices is the bottle neck of developing these future power devices, and thus nano hybrid materials of polymer and ceramics are required to achieve both high thermal conductivity and easy thin film flexible fabrication, namely trade-off function. By the surface modification of BN particles by supercritical method, affinity of BN and polymers could be improved, so that high BN content of hybrid materials, thus high thermal conductivity materials, could be synthesized. By dispersing high refractive index NPs like TiO2 or ZrO2 into polymers transparently, we can tune the refractive index of the polymers. By using supercritical hydrothermal synthesis, organic modified ZrO2, TiO2 nanoparticles could be synthesized. By tuning the affinity of NPs and polymers, we could fabricate the flexible polymer film that has high refractive index and high transparency, namely super hybrid nano materials.
11:15 AM - *GG1.5
Design Rules for Soft Matter Quasicrystals and Complex Crystals
Sharon C. Glotzer 1 Christopher R Iacovella 1 Aaron S Keys 1
1University of Michigan Ann Arbor USAShow Abstract
The surprising recent discoveries of quasicrystals and their approximants in soft matter systems poses the intriguing possibility that these structures can be realized in a broad range of nano- and micro-scale assemblies. We use computer simulation and free energy calculations to demonstrate a simple design heuristic for assembling quasicrystals and approximants in soft matter systems, including nanoparticle-polymer hybrid materials. Our study builds on previous simulation studies of the self-assembly of dodecagonal quasicrystals and approximants in minimal systems of spherical particles with complex, highly-specific interaction potentials. We demonstrate an alternative entropy-based approach for assembling dodecagonal quasicrystals and approximants based solely on particle functionalization and shape, thereby recasting the interaction-potential-based assembly strategy in terms of simpler-to-achieve bonded and excluded-volume interactions. We apply this strategy to systems of polymer-tethered nanoparticles that form micelles, which in turn order into quasicrystalline structures, We argue that this design strategy can be widely exploited to assemble quasicrystals and approximants on the nano- and micro- scales. In addition, our results further elucidate the formation of soft matter quasicrystals in experiment. We also discuss the formation of other complex crystals from polymer-tethered nano particles.
11:45 AM - GG1.6
Self Assembly of Tethered Nanoparticle Telechelics
Ryan Marson 1 Carolyn L Phillips 2 Joshua A Anderson 3 Sharon C Glotzer 3 1
1University of Michigan Ann Arbor USA2University of Michigan Ann Arbor USA3University of Michigan Ann Arbor USAShow Abstract
Recent simulations predict that aggregating nanoparticles functionalized with polymer tethers can self-assemble to form phases seen in block copolymer and surfactant systems, but with additional nanoparticle ordering and mesophase complexity. Here we consider a novel class of â?otelechelicâ? tethered nanoparticle building blocks, where two nanoparticles are connected together by a polymer tether. The architecture is similar to a triblock copolymer, but with additional geometric constraints imposed by the rigid particle end groups. Using Brownian dynamics simulations, we explore the phase diagrams of several examples of this class of nano-building-block, and present predictions of novel phases and their dependence on particle size, tether length and thermodynamic parameters.
12:00 PM - *GG1.7
Role of Parallel Reformable Bonds in the Self-healing of Crosslinked Nanoparticles
Isaac G Salib 1 German V Kolmakov 1 Chet N Gnegy 1 Krzysztof Matyjaszewski 2 Anna C Balazs 1
1University of Pittsburgh Pittsburgh USA2Carnegie Mellon University Pittsburgh USAShow Abstract
We develop a hybrid computational approach to examine the mechanical properties and self-healing behavior of nanogel particles that are crosslinked by both stable and labile bonds. The individual nanogels are modeled via the lattice spring model (LSM), which is an effective method for probing the response of materials to mechanical deformation. The crosslinks between the nanogels are simulated via the Hierarchical Bell Model (HBM), which allows us to capture the rupturing of multiple, parallel bonds due to an applied force. Since the labile bonds are relatively reactive, they can reform after they have been ruptured. To incorporate the possibility of bond reforming, we modify the HBM formalism and validate the modified HBM by considering a system of two surfaces, which are connected by multiple parallel bonds. We then use our hybrid HBM/LSM to simulate the behavior of the crosslinked nanogels under a tensile deformation. In these simulations, each labile linkage between the nanogels contains at most Î parallel bonds. We vary the fraction of labile linkages and the value of Î in these linkages to determine optimal conditions for improving the robustness of the material. While numerous parallel bonds within a linkage enhance the strength of the material, these bonds diminish the ductility and the ability of the material to undergo the structural rearrangements that are necessary for self-repair. For a relatively low fraction of labile bonds and Î â?¤ 4, however, we can significantly improve the strength of the material and preserve the self-healing properties. For instance, a sample with 30% labile linkages and Î = 4 per linkage is roughly 200% stronger than a sample that is crosslinked solely by stable bonds and can still undergo self-repair in response to the tensile deformation. The results reveal how mechanical stress can lead not only to the appearance of cavities within the material, but also the bond formation that â?ohealsâ? these cavities and thus, prevents the catastrophic failure of the material.
12:30 PM - GG1.8
Evaporation-induced Nanoparticle Assembly
Shengfeng Cheng 1 Gary S Grest 2
1Sandia National Laboratories Albuquerque USA2Sandia National Laboratories Albuquerque USAShow Abstract
Large crystalline arrays of nanoparticles that are defect free and nanoparticle-polymer composites with controlled distribution of nanoparticles are critical for a number of technologically important ultrathin film materials including sensors, optical devices and magnetic storage media. One common method for dispersing nanoparticles is to suspend them in solution, spread the suspension on a surface and then evaporate the solvent. Recent experiments have shown that for nanoparticles dispersed in a solvent the rapid evaporation of the latter dynamically produces a two-dimensional solution of nanoparticles at the liquidâ?"air interface, from which nanoparticle islands nucleate and grow. The quality of the nanoparticle film can be controlled by controlling the evaporation rate. Here we present the results of large scale molecular dynamics simulations to study the evaporation-induced assembly of nanoparticles. During solvent evaporation, nanoparticles move toward the liquid/vapor interface and order into a hexagonal lattice. The quality of the order is found to be higher for slower evaporation rates, where fewer defects and grain boundaries are observed. We also examine the structure of polymer nanocomposites during solvent evaporation. Experiments show that very frequently nanoparticles segregate to the surface of polymer thin films after the solvent is evaporated. We observe a rich phase behavior depending on the evaporation rate and the mutual miscibility of the nanoparticles, polymer, and solvent.
12:45 PM - GG1.9
A Method for Quantitatively Characterizing the Dispersion of Nanostructures in Polymer Composites
Steve Pfeifer 1 Prabhakar Bandaru 1
1UC, San Diego La Jolla USAShow Abstract
It is often necessary to quantitatively measure the degree of dispersion of microscopic and nanoscopic entities in a macroscopic polymer matrix. As an example for illustrating the applicability of such a notion, composites constituted of zero and lower dimensional nanostructures placed in a polymer have been widely proposed for electromagnetic interference (EMI) shielding, in high sensitivity infrared sensors, structural applications, etc.. It has also been generally accepted in the community that the composite properties would be optimal when the nanostructures/nanoparticles are uniformly dispersed within the polymer matrix. The uniform dispersal and bonding of the particles in a polymer may confer unique properties to the composite, e.g. through the postulated, formation of an interphase region, enhanced charge carrier scattering, etc. However, there is at present no uniformly accepted metric to gauge the uniformity of dispersion of the nanostructures in the polymers. Additionally, current notions of uniformity of dispersion are either too qualitative or do not have a strong mathematical foundation. We then present in this paper, an experimental methodology for quantifying the degree of dispersion of nanoparticles in polymers. Our proposed measure of dispersion, the d-metric (â?¡ d(P||Q)) is based on fundamental and well established information theory principles that are used to correlate randomness to the dispersion. This allows a quantitative comparison of the given distribution (say, P) to a preferred distribution or pattern (say, Q). We then provide examples from our own studies and those from literature on the application of the metric. Specific studies on the dispersion of alumina nanoparticles in a polyethylene terephthalate (PET) polymer matrix will be considered.
Symposium OrganizersJoseph B. Tracy, North Carolina State University
Yadong Yin, University of California, Riverside
Nicole S. Zacharia, Texas Aamp;M University
Unyong Jeong, Yonsei University
Symposium Support Army Research Office
GG8: Block Copolymer-Based Systems
Wednesday PM, April 11, 2012
Moscone West, Level 3, Room 3011
2:30 AM - *GG8.1
Co-continuous Nano-structured Polymer Membranes via Spinodal Decomposition of Homopolymer Blends with Nanoparticles and Random Copolymers
Le Li 1 Xiaobo Shen 1 Sung Woo Hong 1 Todd S Emrick 1 Ryan Hayward 1 Thomas Russell 1
1University of Massachusetts Amherst USAShow Abstract
Simple approaches to prepare co-continuous micro-structured blends of polymers are presented. With nanoparticles, the formation of a percolating network of particles within one phase of a polymer mixture undergoing spinodal decomposition is demonstrated. Nanorods and nanospheres of CdSe were added to near-critical blends of polystyrene and poly(vinyl methyl ether) quenched above their lower critical solution temperature (LCST). Beyond a critical loading of nanoparticles, phase separation is arrested due to the aggregation of particles into a network (or colloidal gel) within the poly(vinyl methyl ether) phase, yielding a co-continuous spinodal-like structure with a characteristic length scale of several microns. The size scale of the co-continuous domains was reduced to the tens of nanometers using solvent cast mixtures of polystyrene (PS) and poly(2-vinylpyridine) (P2VP) where miscibility was controlled by incorporating styrene monomers into the backbone of P2VP to form a random copolymer. The co-continuous structure size is controlled by varying the molecular weights of the homopolymer PS and the random copolymers, as well as the film thickness. This solvent-induced phase separation was robust, provided the solvent dissolved both components, and insensitive to the substrate surface chemistry.
3:00 AM - GG8.2
Diblock Copolymer - Nanocrystal Hybrids with Improved Nanostructure for Optoelectronic Applications
Lisa zur Borg 1 Jaehoon Lim 2 4 Donggu Lee 3 Chang-Hee Lee 3 Seonghoon Lee 4 Kookheon Char 2 Rudolf Zentel 1
1Johannes Gutenberg-University Mainz Germany2The National Creative Research Initiative Center for Intelligent Hybrids, Seoul National University Seoul Republic of Korea3Inter-University Semiconductor Research Center, Seoul National University Seoul Republic of Korea4Seoul National University Seoul Republic of KoreaShow Abstract
Semiconducting polymers combined with inorganic semiconductors offer exciting possibilities for optoelectronic devices like LEDs or OSCs,. They are flexible and lightweight, and have high absorption coefficients. The properties of the polymers can be adjusted according to need, by systematically tuning their chemical structure. The inorganic semiconductors on the other hand, bring high charge carrier mobility and a high dielectric constant. Nanostructured materials in particular, such as quantum dots or tetrapods, display fascinating properties because of the quantum size effect, and can also be fine-tuned during synthesis. By bringing these two materials together, hybrids are formed with improved performance. The control of the morphology between the inorganic and organic part was achieved by synthesizing novel block copolymers. To create a good interphase, we utilize a long, solubility-enhancing semiconducting block, and a short anchor block. The polymers are bound strongly to the inorganic material due to the chelate effect. We show that CdSe tetrapods which are functionalized with a block copolymer are well dispersed into the polymer matrix. On the contrary, a blend consisting of tetrapods and polymer without anchoring groups shows aggregates and a poor film formation. The assembly of the hybrid system can be precisely tuned by adjusting the amount of polymer on the surface. This morphology is considered ideal for hybrid solar cells because the tetrapods form a large interconnected network, with their thin arms allowing the exciton to easily dissociate. Two different kinds of polymers have been synthesized: Poly-(p-phenylene vinylene) (PPV) with a defined end group by Siegrist polycondensation and a modified triphenylamine based polymer by Reversible Addition Fragmentation Chain Transfer (RAFT) Polymerization. Both polymers are well known for optoelectronic devices. Block copolymers were synthesized carrying active ester groups, and amine anchoring groups were attached in a second step. Hybrids of the CdSe tetrapods with these polymers were formed and showed improved properties. Especially the PPV block copolymer offers a great variety of new functional block copolymers, because nearly any functionality can be easily introduced. The precise control of the morphology of the hybrids as shown here, offers various new possibilities. Now, with these advanced materials, the opportunity has arrived for a new range of applications for optoelectronic devices to be realized. References  P. Reiss, E. Couderc, J. De Girolamo and A. Pron, Nanoscale, 3, 446-489 (2011)  J-H. Kwak, W-K. Bae, M. Zorn, H-J. Woo, H-S. Yoon, J-H. Lim, S-W. Kang, S. Weber, H-J Butt, R. Zentel, S. Lee, K. Char and C-H. Lee, Advanced Materials, 21, 5022-5026 (2009)
3:15 AM - *GG8.3
Block Copolymer Mediated Inorganic Nanostructures
Ho-Cheol Kim 1
1IBM Almaden Research Center San Jose USAShow Abstract
Microphase separation of block copolymers provides well defined nanostructures. While numerous effort has been devoted to investigate the self-assembly behavior of block copolymers (for example, thin films of block copolymers), to use them as a structure directing agent has been attracted great interest as well in terms of generating nanostructures of functional inorganic materials through self-assembly. In this talk, Iâ?Tll discuss our effort to understand and control the nanostructures of block copolymer containing hybrid materials. The discussion will include nanostructures of silicates, titania and semiconductor nanocrystals. Applications to fabrication of devices and the effect of nanostructures on their performance will be addressed as well.
3:45 AM - GG8.4
High-throughput Directed Self-assembly of Core-shell Nanoparticle-polymer Composites
Alshakim Nelson 1 Qiu Dai 1 Joy Cheng 1 Jane Frommer 1 Kumar Virwani 1
1IBM Almaden Research Center San Jose USAShow Abstract
Nanoparticles represent a versatile set of building blocks for constructing functional materials with properties that can be exploited for both existing and emerging technologies. Although many of these applications would significantly benefit from the organization of nanoparticles into higher order architectures, the precise placement and arrangement of nanoparticles over large areas of a surface remain a challenge. Here, we present a simple and facile strategy for high-throughput directed self-assembly of nanoparticles on lithographically defined substrates via spin-coating. Ferrimagnetic nanoparticles were stabilized in solution with a diblock copolymer to form nonaggregating core-shell composite nanoparticles. The polymers enable the self-assembly of these particles from solution onto the patterned substrates. The two-dimensional arrangement of nanoparticles that is formed is determined by the strategic placement of resist features on the substrate. For example, circular and star-shaped arrangements of nanoparticles, wherein the diameter of the self-assembled structure can be controlled from several hundred nanometers to a few microns, were formed by controlling the size and geometric arrangement of the resist features. In addition to the precise arrangement and registration of the nanoparticle assemblies on the substrates, all of the assemblies were formed in just 30 seconds of spin-coating. Ferrimagnetic nanoparticles, assembled using this method, were further investigated using magnetic force microscopy (MFM). This high-throughput self-assembly of functional nanostructures over large areas demonstrates the scalablity of fabricating future devices and materials using processes compatible with current semiconductor manufacturing techniques.
4:30 AM - *GG8.5
Designing Polymer-coated Nanoparticle ``Surfactants'' to Control Block Copolymer Morphology
Se Gyu Jang 3 Anzar Kahn 3 Bumjoon J Kim 4 3 Michael D Dimitriou 1 3 Nate A Lynd 3 Glenn H Fredrickson 4 3 Craig J Hawker 1 2 3 Edward J. Kramer 1 4 3
1UC Santa Barbara Santa Barbara USA2UC Santa Barbara Santa Barbara USA3UC Santa Barbara Santa Barbara USA4UC Santa Barbara Santa Barbara USAShow Abstract
End-functional polymer ligands grafted to form brushes on inorganic nanoparticles, the polymer-coated nanoparticles of the title, provide useful probes to reveal the fundamentals of block copolymer/nanoparticle co-assembly. Lamellar block copolymers of poly(styrene-b-2vinylpyridine) PS-b-P2VP of molecular weights ranging from 114 to 380 kg/mol are used as a model system. Short thiol terminated polymer ligands are synthesized to allow Au nanoparticles (~ 1.5 nm radius Au core) coated with polymer brushes to be prepared. Using either anionic or controlled radical polymerization, end-functional polymer ligands can be synthesized with homopolymer, random copolymer or even block copolymer architecture. Diblock copolymer ligands of PS-b-PI-SH where the short 1,2&3,4 polyisoprene (PI) block can either be crosslinked by hydrosilation to provide thermal stability or hydroxylated (PIOH) to provide hydrogen bonding capability to the P2VP block. The nanoparticles with crosslinked ligand shells are thermally stable for days at 190 Â°C but yet segregate to PS-b-P2VP interface, at high enough volume fractions causing a transition from lamellar to bicontinuous morphology. Au nanoparticles coated by block copolymer ligands with a PIOH shell are soluble in nonpolar solvents due to the outer PS ligand brush yet will hydrogen bond to the P2VP block of the PS-b-P2VP and, depending on the length of the PIOH inner block, nanoparticles coated with such ligands can be directed to the PS-b-P2VP interface or into either the P2VP or PS domains. In the latter case a novel â?opea-podâ? arrangement of the nanoparticles in the PS lamellae is observed.
5:00 AM - GG8.6
Chemically Assembled SERS Substrates: Au Nanoparticle Clusters on Diblock Copolymer Templates
Sarah Marie Adams 1 Joshua Caldwell 2 Regina Ragan 1
1UC Irvine Irvine USA2Naval Research Laboratory Washington USAShow Abstract
Assembly of metal nanoparticles into architectures with molecular scale interparticle separations result in enhanced optical fields on surfaces, having applications to lower detection limits in sensors and enhance absorption in the active region of solar cells. We will present results on the planar assemblies of monodisperse Au nanoparticles that were formed in clusters with interparticle separations unachievable using lithographic methods on low-cost substrates using self-organization processes. Using chemical self-assembly, we have attached monodisperse, colloidal gold nanoparticles on self-organized polymer templates, patterning arrays of nanoparticle clusters with sub-10 nanometer interparticle separations. Poly(methyl methacrylate) (PMMA) domains in phase-separated PS-b-PMMA diblock copolymer thin films were chemically modified with surface amine functional groups for controlled arrangements. Chemically synthesized gold nanoparticles, from 10 nm and 20 nm sample sets, were attached to the amine-functionalized PMMA surface domains using 1-Ethyl-3-[3-dimethylaminopropyl] carbodiimide hydrochloride (EDC) cross-linking chemistry with thioctic acid ligand-bound to the nanoparticle surface, preferentially immobilizing the Au nanoparticles on PMMA domains of the copolymer template. By using chemical assembly techniques, versatility of size and shape of nanoparticles and cluster arrangements are achievable in the patterned planar surface. By controlling nanoparticle diameter relative to PMMA domain size, nanoparticle clustering was controlled. As the diameter of nanoparticles was decreased relative to the size of the amine-functionalized PMMA regions, larger numbers of Au nanoparticles were localized on each individual nanoparticle cluster domain. These dense arrays of closely spaced nanoparticles were characterized and have demonstrated advantageous benefits for field-enhanced biochemical sensors using surface enhanced Raman scattering (SERS). SERS measurement of the planar nanoparticle assemblies showed uniform signal enhancement across each samples with 107 maximum signal intensity enhancement factor and reusability of SERS substrates with simple analyte removal between application.
5:15 AM - *GG8.7
Direct Hierarchical Assemblies of Nanoparticles with High Precision
Ting Xu 1
1University of California, Berkeley Berkeley USAShow Abstract
Controlled assembly of functional building blocks, such as nanoparticles, over multiple length scales has great potential to advance technologies. However, generating hierarchically structured nanocomposites in a manner similar to that seen in nature represents a fundamental scientific challenge. We recently developed a simple, yet versatile approach to produce stimuli-responsive hierarchical assemblies of readily available nanoparticles by combining small molecules and block copolymers (BCPs). BCPs microphase separate and form well-defined nanostructures in tens of nanometer and provide ideal framework to assemble nanoparticle from tens of nanometers to macroscopic distances. By hydrogen bonding small molecules that favorably interact with the nanoparticle ligands to the polymer side-chains, nanoparticle-polymer interactions can be tailored. Organization of small molecules within BCP microdomains provides a unique handle to tailor nanoparticle assemblies with high precision. Using this approach, organization of nanoparticles into one, two and three-dimensional arrays with controlled inter-particle separation and ordering is achieved without chemical modification of either the nanoparticles or BCPs. Recently, we expanded this approach to obtain ordered arrays of nanoparticles in thin films. The unique architecture of supramolecules and favorable interactions between the small molecules and nanoparticle ligands balance the enthalpic and entropic driving forces that lead to the segregation of nanoparticles to the surface of film, resulting in surface-guided 3-D assemblies of nanoparticles. The long-range lateral ordering of nanoparticle assemblies can be readily achieved using a saw-tooth patterned substrate. Combining the sub-particle-diameter precision in the spatial location of the nanoparticles and the long-range lateral order with the rapid processing time, the approach described provides a unique platform to fabricate a wide range of nanodevices for energy harvesting and storage, catalysis, sensing, optical waveguide and nanoelectronics.
GG6: Layer-by-Layer Assembly II
Wednesday AM, April 11, 2012
Moscone West, Level 3, Room 3011
9:30 AM - *GG6.1
Water-Based Rapid Assembly of Hybrid Nanomaterials for Electrochemical Electrodes
Nasim Hyder 1 Sung Yeol Kim 1 Kittipong Saetia 1 Yang Shao-Horn 2 Paula T. Hammond 1
1Massachusetts Institute of Technology Cambridge USA2Massachusetts Institute of Technology Cambridge USAShow Abstract
We have recently demonstrated the ability to assemble nanotubes, nanoparticles, and a range of other organic and inorganic nanostructured materials onto substrates using the electrostatic layer-by-layer (LbL) assembly approach to achieve asymmetric electrochemical capacitors and battery electrodes that exhibit unusually high power and high energy density. We have now extended our work to include conjugated polymer nanofibers and titania nanostructures, or metal oxide nanoparticles, for electrochemical capacitors with even higher energy capacity. Furthermore, it is possible to scale up the LbL process using newly devised approaches to Spray-LbL that enable the formation of dense nanotube arrays that are several microns or more in thickness over short periods of time. Templating on porous systems and generation of new architectures enable the translation of nanoscale architectures formed from disperse nanomaterials to micron to millimeter length scales. By tuning the surface chemistry of the carbon nanotubes, and carefully selecting other nanomaterials that enable charge insertion or facilitate charge transport, we can design a broad range of materials systems with applications that range from electrochemical energy to sensing and storage applications.
10:00 AM - GG6.2
Composites by Design: Novel Properties of Three-Dimensional Layer-by-Layer Assembled Materials with Controlled Multiscale Architecture
Christine M. Andres 1 Nicholas A Kotov 1
1University of Michigan Ann Arbor USAShow Abstract
Hybrid nanocomposites create functional materials with enhanced and diversified properties as compared to their bulk counterparts. Three-dimensional architecture adds to these impressive properties by allowing for the addition of unique characteristics such as special deformation patterns, negative Poisonâ?Ts ratio, negative thermal expansion coefficients, propagation of electromagnetic waves, controlled biological interactions, and mass transport properties. Typical methods for preparing materials with 3D microscale features are often restricted by limited material variability, lack of control over the nanophase and challenging transitions to macroscale materials. This work describes a new method to introduce controlled multiscale architecture into freestanding, functional composites by using layer-by-layer assembly (LBL), the sequential adsorption of monoloyers attracted by chemical forces, to strategically fill the void space of templates from ordered arrays of uniform microspheres. The technique allows for systematic control of chemical and structural features of polymer nanocomposites from the molecular scale through the macroscale. Establishing appropriate techniques to produce materials involving features across multiple scales with fairly independent control at all levels allows for the investigation of structural influences on macroscale material properties, including mechanical, thermal and electrical properties. Considering the unique properties of planar LBL nanocomposites, currently unattainable by alternate techniques, the method allows for new practical applications due to the unusual combinations of properties that can be achieved by such controlled assembly of composite materials.
10:15 AM - *GG6.3
Tailoring Gas Permeability and Imparting Flame Retardant Behavior Using Nano Brick Wall Thin Film Assemblies
Jaime Grunlan 1 2 3
1Texas Aamp;M University College Station USA2Texas Aamp;M University College Station USA3Texas Aamp;M University College Station USAShow Abstract
Layer-by-layer (LbL) assembly of montmorrilonite (MMT) clay and various polyelectrolytes result in nano brick wall thin films with impressive oxygen barrier and flame retardant behavior. Sixteen polymer-clay layers results in a film less than 60 nm thick with an undetectable oxygen transmission rate (< 0.005 cc/m2 day) at room temperature. This film has oxygen permeability lower than that reported for SiOx-coated or metalized plastic film, making it a transparent foil replacement (for food and flexible electronics packaging). When similar clay-based thin films are deposited on cotton (or polyester) fabric and polyurethane foam, they create a char forming layer that reduces peak heat release rate and eliminates melt dripping (in the case of foam). In an effort to create an even more environmentally-friendly flame retardant system for foam, ten bilayers (~ 30 nm thick) of pH 6 chitosan (CH), as the cationic layer, and pH 10 MMT as the anionic layer, were deposited. Only the outermost surface was charred after being exposed to the direct flame from a propane torch for 10 seconds. Cone calorimetry revealed that this protective nanocoating, which increased the foamâ?Ts weight by only 4%, reduced the peak heat release by 52% relative to the uncoated control. These results demonstrate the first truly â?ogreenâ? LbL flame retardant. All of the properties of these thin films can be tailored by altering pH, concentration, and ionic strength of deposition mixtures, along with varying the type of polycation.
10:45 AM - GG6.4
Hierarchical Nanoflake Surface Driven by Spontaneous Wrinkling of Polyelectrolyte/Metal Complexed Films
Young Hun Kim 1 Yong Man Lee 2 Jong Hyeok Park 1 2 Pil J. Yoo 1 2
1Sungkyunkwan University Suwon Republic of Korea2Sungkyunkwan University Suwon Republic of KoreaShow Abstract
A mechanical or physical change observed in nanocomposite thin films has recently offered new opportunities to generate intriguing nanostructures. In this study we present a novel means of creating a hierarchically developed nanoflake structure by exploiting surface wrinkles that occur during the impregnation process of metallic nanoparticles with layer-by-layer assembled polyelectrolyte multilayer (PEM) thin films. The polyelectrolyte multilayer film comprised with linear polyethylenimine (LPEI) and poly(acrylic acid) (PAA) allows for interdiffusion even after the electrostatic complexation and chemical crosslinking reaction, which enables a facilitated cationic exchange reaction within the film. The subsequent reduction process induces an in-situ complexation of metallic nanoparticles with a polyelectrolyte multilayer matrix, causing an accumulation of lateral compressive stress for surface wrinkling. The wrinkling characteristics of the complexed films can be theoretically interpreted by employing the gradationally swollen film model, whereby a gradual change in the elastic property along the axial direction of the film can be appropriately reflected. In addition, wrinkled surfaces are further processed to form vertically aligned and hierarchically ordered nanoflakes after selective removal of the polyelectrolyte multilayer matrix with plasma-ashing. Consequently, superhydrophobic surface properties (dynamic water contact angle = 170 degrees, sliding angle < 1 degree) can be attained from the hierarchical nanoflake structure. The method presented here is advantageous in that large-scale preparation can be readily implemented by a stepwise dipping process without resorting to specific patterning or a serially applied complex structuring process, which can provide a promising platform technique for various surface engineering applications.
GG7: Field-Directed Self-Assembly
Wednesday AM, April 11, 2012
Moscone West, Level 3, Room 3012
11:30 AM - *GG7.1
Precise Directed Assembly of Colloidal Particles into Materials with Engineered Structure and Properties
Orlin D Velev 1
1NC State University Raleigh USAShow Abstract
We will overview a few strategies for controlled assembly of micro- and nanoparticles into highly structured materials and will discuss how the issues of scalability, control and precision could be addressed in such processes. In the first part of the talk we'll discuss how controlled drying of liquid suspensions confined in thin menisci or in droplets deposited on surfaces can be used for efficient assembly in two and three dimensions. The organization of the particles is a result of a complex combination of convective transport and capillary forces at the liquid/air interface. The process of convective assembly can be engineered at high particle volume fractions in order to deposit structured nanocoatings with maximal velocity. An alternative process for assembly of self-contained supraparticles that we have developed involves drying of sessile suspension droplets. The dynamic shape of the liquid surface guiding the assembly can be controlled to form particle crystals in the form of spheres, hemispheres, ellipsoids or "doughnuts". In the second part of the talk we will focus on more complex and precise methods for assembly by electric and magnetic fields. Examples of field-driven assembly of nanoparticles, microspheres, â?oJanusâ? and â?opatchyâ? particles will be presented and interpreted from the perspective of the field-induced forces and interactions. We will demonstrate how the field parameters can be used for efficient control and modification of the process and how the use of complex particles can result in field-programmed materials assembly.
12:00 PM - *GG7.2
Synthesis of and Colloidal Polymerization of Heterostructured Dipolar Nanoparticles
Jeffrey Pyun 1 2
1University of Arizona Tucson USA2Seoul National University Seoul Republic of KoreaShow Abstract
We will discuss our recent efforts in the synthesis of dipolar colloids to prepare heterostructured cobalt oxide nanowires. The synthesis of ferromagnetic nanoparticles based on metallic cobalt offers a facile route to self-assembling dipolar chains. By modification of cobalt nanoparticles with metallic noble metal inclusions (Au, Pt), or n-type semiconductors (CdSe, CdS), the preparation of complex dipolar colloids has been achieved. We will also discuss our developments in using these dipolar nanoparticles as â?ocolloidal monomersâ? for Colloidal Polymerization to prepare cobalt oxide nanowires that carry these nanoinclusions in the interior, or exterior of the 1-D assembly. Synthesis, characterization and evaluation of potential applications of these materials for energy storage and conversion will be discussed
12:30 PM - GG7.3
Magnetic Field-directed Self-assembly of Magnetic Nanoparticle Chains in Bulk Polymers
Peter J Krommenhoek 1 Richard J Spontak 2 1 Joseph Benjamin Tracy 1
1North Carolina State University Raleigh USA2North Carolina State University Raleigh USAShow Abstract
There is a great need for approaches to assemble nanoparticles in three dimensions and to preserve the assembled structure. We report a template-free approach for the magnetic field-directed self-assembly of chains of 25 nm magnetite nanoparticles in a bulk polymer, in which all three dimensions are 1 cm or greater. Application of a uniform 10 kOe magnetic field drives chain formation within liquid monomers (a mixture of lauryl methacrylate and ethylene glycol dimethacrylate). Heating initiates polymerization of the monomers, resulting in magnetic nanoparticle chains embedded in a solid polymer. Repulsive forces between the chains cause them to assemble into an array with quasiperiodic, micron-scale spacing. According to electron microscopy and electron tomography, the chains remain assembled within the polymer indefinitely after removing the magnetic field. The optical absorbance of the chains is much greater when they are oriented perpendicular rather than parallel to incident light, and they exhibit enhanced magnetic anisotropy along the chain axis. This approach of magnetic field-directed self-assembly is potentially scalable to large volumes, limited only by the size of the electromagnet. This fabrication strategy of magnetic-field assisted nanoparticle assembly, successfully applied to a single polymer during polymerization, is also applied to a physical blend of two immiscible thermoplastics: polystyrene (PS) and poly(methyl methacrylate) (PMMA). Thin and thick films of PS/PMMA blends differing in composition are cast from toluene suspensions containing varying concentrations of magnetite nanoparticles in a uniform magnetic field. The effects of the magnetic field-directed assembly of magnetite nanoparticles on polymer blend morphology are investigated by optical and electron microscopy and compared to blend morphologies generated without nanoparticles, as well as with nanoparticles and no applied field.
12:45 PM - GG7.4
Long-Range Alignment of Gold Nanorods in Electrospun Polymer Nano/Microfibers
Kristen E Roskov 1 Krystian A Kozek 2 Wei-Chen Wu 2 Raghav K Chhetri 3 Amy L Oldenburg 3 Richard J Spontak 1 2 Joseph Benjamin Tracy 2
1North Carolina State University Raleigh USA2North Carolina State University Raleigh USA3University of North Carolina at Chapel Hill Chapel Hill USAShow Abstract
A scalable fabrication technique for controlling and maintaining the nanoscale orientation of gold nanorods (GNRs) with long-range macroscale order has been achieved through electrospinning. Low aspect-ratio GNRs were dissolved in aqueous poly(ethylene oxide) solutions and electrospun to generate fibers possessing different GNR concentrations (up to 4.5 vol%) and diameters measuring between 40 and 3000 nm. The GNRs aligned within the fibers with their long axes parallel to the fiber axis. The average deviant angle between the GNR long axis and the fiber axis increases modestly as the fiber diameter increases. Complementary electron diffraction measurements confirm preferred orientation of the GNR crystal planes. Optical absorbance spectroscopy measurements reveal that the longitudinal surface plasmon resonance bands of the aligned GNRs depend on the polarization angle and that maximum extinction occurs when the polarization is parallel to the fiber axis.