Erik Luijten University of Illinois, Urbana-Champaign
Sharon C. Glotzer University of Michigan-Ann Arbor
Francesco Sciortino Universitá di Roma “La Sapienza”
CC1: Self-assembly of Anisotropic Particles
Tuesday PM, December 02, 2008
Fairfax A (Sheraton)
9:30 AM - **CC1.1
Assembly of Divalent Nanoparticles.
Francesco Stellacci 1 Show Abstract
1 Materials Science and Engineering, MIT, Cambridge, Massachusetts, United States
When a mixture of dislike ligand molecules forms a self assembled monolayer on the core of a gold nanoparticle striated worm-like domains of alternating composition spontaneously form. This unique phase separation pattern leads to the formation of two diametrically opposed point defects that can be selectively chemically modified. A full thermodynamic analysis of the reactivity of these point defects will be presented. Moreover the assembly of these 'divalent' particles in chains and other patters will be discussed. Finally chains of superparamagnetic iron oxide nanoparticles with a blocking temperature 40 K higher than their nanoparticles compontents will be presented.
10:00 AM - **CC1.2
Self-Assembly of Nanostructured Materials.
Bartosz Grzybowski 1 2 Show Abstract
1 Chemistry & Chem. Biol. Eng, Northwestern University, Evanston, Illinois, United States, 2 Chemistry, Northwestern University, Evanston, Illinois, United States
Self-assembly of nanoscopic components into higher-order architectures defines the forefront of fundamental nanoscience research and is important for the development of new materials with potential applications in optoelectronics, high-density data storage, catalysis, and biological sensing. In my talk, I will discuss how the peculiar nature of electrostatic and photoinduced dipole-dipole forces acting between nanoscale components can mediate their self-assembly into various superstructures and materials. I will show how the interactions underlying self-assembly can be studied and understood in quantitative detail, and how they can be tailored to synthesize unusual higher-order architectures: ionic-like crystals of nanoparticles, crystalline aggregates that can be assembled and disassembled by light, as well as extremely durable and yet very flexible metallic structures. Since these materials display a range of novel optical, electrical and mechanical properties, the discussion of experimental results will be accompanied by theoretical analyses combining elements of thermodynamics, statistical mechanics, electrodynamics and elasticity.
10:30 AM - **CC1.3
Nanoparticle with Protein-like Anisotropy: From Self-organization to Nanoscale Biosensing Devices.
Nick Kotov 1 Show Abstract
1 , U Michigan, Ann Arbor, Michigan, United States
Physical properties of nanoparticles and nanowires are currently well understood. The next frontier is conceptualization of larger structures, such as nanoscale assemblies. This talk will discuss the two paradigms in this field: (1) spontaneous assemblies of nanoparticles and (2) quantum mechanical interactions of metallic and semiconductor building blocks in nanoscale assemblies. Anisotropic forces arising between nanocrystalline particles drive the self-assembly behavior of these colloidal particles. Interaction anisotropy between CdTe nanoparticles in solution leads to their spontaneous, template-free organization into free-floating sheets. Electrostatic interactions arising from a dipole moment and a small positive charge combined with directional hydrophobic attraction between the nanoparticles are the driving forces for the self-assembly, which we demonstrate by computer simulation. We found that nanoparticles show conceptual similarities with assembly of proteins. This supposition was recently confirmed by assembly of nanoparticles into spiral systems similar to those found in many biological systems. Electronic interactions in nanoparticle assemblies represent one of the fundamental problems of nanotechnology. Excitons and plasmons are the two most typical excited states of nanostructures, which were shown to produce coupled electronic systems. The concept of these interactions between the Au and CdTe nanoparticles and nanowires will be discussed in terms of quantum mechanical coupling of excited states and unusual optical effects. As such, in presence of dynamic component for excitons theory predicts that emission of coupled excitations in nanowires with variable electronic confinement is stronger, shorter, and blue-shifted. These predictions were confirmed with high degree of accuracy in molecular spring assemblies, where one can reversibly change the distance between the exciton and plasmon. The prepared systems were made protein-sensitive by incorporating antibodies in molecular springs. Modulation of exciton-plasmon interactions can serve as wavelength-based biodetection tool, which can resolve difficulties of quantification of luminescence intensity for complex media and optical pathways.
11:30 AM - **CC1.4
Hybrid Assembly and the Role of Malleable Molecules.
Phill Geissler 1 , Stephen Whitelam 1 , Carl Rogers 1 Show Abstract
1 Chemistry, U.C. Berkeley, Berkeley, California, United States
12:00 PM - CC1.5
Predicting Self-Assembled Structures from Strongly Interacting Nanoparticles and Colloids.
Eric Jankowski 1 , Sharon Glotzer 1 Show Abstract
1 Departments of Chemical Engineering and Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan, United States
12:15 PM - CC1.6
An Ordered Mesoporous Metal from Nanoparticle-Block Copolymer Self-Assembly.
Scott Warren 1 2 , Lauren Messina 2 , Liane Slaughter 2 , Marleen Kamperman 1 , Qin Zhou 2 , Sol Gruner 3 , Francis DiSalvo 2 , Ulrich Wiesner 1 Show Abstract
1 Materials Science & Engineering, Cornell University, Ithaca, New York, United States, 2 Chemistry & Chemical Biology, Cornell University, Ithaca, New York, United States, 3 Physics, Cornell University, Ithaca, New York, United States
Since the pioneering synthesis of SBA-15 mesoporous silica by Stucky et al. in 1998, the field of mesoporous ceramics self-assembled from block copolymers has grown rapidly. This self-assembly concept has been extended to transition metal oxides, non-oxide ceramics, and carbon. Here we present the extension of this concept to metals. We first synthesized ligand-stabilized platinum nanoparticles with a low ligand density, intended to partially expose part of the platinum surface. We self-assembled these patchy particles with a poly(isoprene-block-dimethylaminoethylmethacrylate) block copolymer (PI-b-PDMAEMA), which produced an ordered mesostructured hybrid with an inverse hexagonal morphology. The use of patchy platinum particles was an essential part of the self-assembly process; the partially exposed platinum surface allowed enthalpically favorable platinum-polymer interactions to occur in which the amine of the polymer probably chemisorbed onto the platinum surface. The hybrid was converted into an ordered mesoporous platinum-carbon nanocomposite by a pyrolysis process and the carbon was removed by either a plasma treatment or an acid etch. The resulting ordered mesoporous platinum was electrocatalytically active for hydrogen oxidation. This work demonstrates the power of working with patchy platinum nanoparticles with carefully controlled ligand densities for the self-assembly of ordered mesoporous metals.
12:30 PM - CC1.7
Self Assembly of Colloidal Particles at Small Number.
Guangnan Meng 1 2 , Natalie Arkus 2 , Ryan McGorty 1 , Michael Brenner 2 , Vinothan Manoharan 1 2 Show Abstract
1 Physics, Harvard University, Cambridge, Massachusetts, United States, 2 SEAS, Harvard University, Cambridge, Massachusetts, United States
12:45 PM - CC1.8
Non-cubic Self-organization of Single-component Nanoparticles with Soft, Reconfigurable Corona.
Hilmar Koerner 1 , Folusho Oyerokun 1 , Maxim Tchoul 1 , Richard Vaia 1 , Sanat Kumar 3 , Yu Li 2 , Douglas Duke 2 , Brian Benicewicz 4 , Linda Schadler 2 Show Abstract
1 , Air Force Research Laboratory, Wpafb, Ohio, United States, 3 , Columbia University, New York City, New York, United States, 2 , Rensselaer Polytechnic Institute, Troy, New York, United States, 4 , University of South Carolina, Columbia, South Carolina, United States
Meso-scale organization pervades organic, macromolecular and biomolecular systems. For example, units lacking an inversion center (non-centrosymmetric), such as surfactants and di-block copolymers, are known to organize, depending on details of the molecular architecture, into lamellae, cylinders and complex 3D structures. The polar nature of these units is generally considered a requirement for organization into such mesoscale structures. Recent scattering experiments and theoretical modeling though indicate that a centrosymmetric nanoparticle with a soft, reconfigurable corona can “respond” to inter-particle interactions, resulting in an energetically-favorable quadrupolar distortion of the corona and non-cubic mesoscale organization. For example, depletion forces acting on high molecular weight chains that are tethered to the nanoparticle surface at a density below the mushroom to brush transition lead to lamellar organization of the nanoparticle center of mass. Specifically, 15 nm silica surrounded by 120kg/mol polystyrene at a grafting density of 0.05chains/nm2 (50 vol % silica) yield robust films consisting of lamellar morphology, in which fibers can be drawn at temperatures above 120C. To establish an understanding of structure formation, the structural and physical characteristics of a systematic series of silica nanoparticles of variable core size, tethering density and molecular weight is discussed. The high inorganic content (30-60vol%) of these single-component nanoparticles with soft, reconfigurable corona will have broad implications to civil and defense applications, with initial payoffs seen for ultrahigh density capacitors.
CC2: Synthesis of Patchy and Anisometric Particles
Tuesday PM, December 02, 2008
Fairfax A (Sheraton)
2:30 PM - **CC2.1
Synthesis, Manipulation and Assembly of Engineered Particles having Controlled Shape, Size and Surface Chemistry.
Joseph DeSimone 1 2 , Kevin Herlihy 1 , Janine Nunes 1 , Stephanie Gratton 1 , Stephen Jones 1 Show Abstract
1 Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States, 2 Chemical Engineering, North Carolina State University, Raleigh, North Carolina, United States
On the quest for the fabrication of micro- and nano-scale machines, assemblies of small pieces of equipment, capable of interacting both with each other and responding to external stimuli are a necessity. Using a novel technique known as Particle Replication In Non-wetting Templates (PRINT), we have fabricated particles with a variety of distinct shapes and sizes that are suitable for this task. We have shown the alignment and formation of crystalline assemblies of our non-spherical particles in solution under the influence of AC electric fields via dielectrophoresis. Other particles were loaded with iron oxide and were manipulated in solution by applying an external magnetic field. Additionally, the surfaces of the particles were selectively functionalized to fabricate Janus-type particles. This was done by altering the chemistry of the particles while they were either 1.) trapped in the mold or 2.) in arrays bound to an adhesive layer. This will allow the fabrication of reversibly interlocking pieces and self-propelled, remotely steered particles taking us a step closer to functional nano-machines. In addition to materials applications, these non-spherical particles can be utilized in life science applications in order to probe the mechanism of cellular entry. Preliminary studies were performed in which particles were dosed onto mouse macrophage cells in order to observe the effect of directed cellular entry. In these studies, one side of the particles were coated with an antibody that promotes internalization selectively over the other sides of the particle. The results of these early experiments and the implication of end-functionalization in both life science and materials science applications will be discussed.
3:00 PM - **CC2.2
Stop Flow Lithography to Create Functional Anisotropic Microparticles.
Priyadarshi Panda 1 , T. Alan Hatton 1 , Patrick Doyle 1 Show Abstract
1 Chemical Engineering, MIT, Cambridge, Massachusetts, United States
3:30 PM - CC2.3
Anisotropically Phase-Segregated Inorganic Nanoparticles: Synthesis and Structure-Specific Functions.
Toshiharu Teranishi 1 Show Abstract
1 Department of Chemistry, University of Tsukuba, Tsukuba, Ibaraki, Japan
Recently, anisotropically phase-segregated nanoparticles have been accessible and received much attention due to two important features, namely, the simultaneous use of plural functions, such as the luminescent and magnetic properties, and the directed assembly of nanoparticles by anisotropically arranging the different ligands at the surface of these particles . We succeeded in the spontaneous formation of anisotropically two phase-segregated Co9S8/PdSx (CoPd sulfide) nanoparticles (nanoacorns) . Furthermore, the PdSx seed-mediated synthesis on the basis of our proposed mechanism for the formation of CoPd sulfide nanoacorns gave the anisotropically three phase-segregated PdSx/Co9S8/PdSx (PdCoPd sulfide) nanoparticles (nanopeanuts) .Another important feature of anisotropically phase-segregated nanoparticles is that the atom diffusion can occur at the interface between two inorganic phases. Recently, we have succeeded in the novel synthesis of fct-FePd/α-Fe nanocomposite magnets via the interfacial atom diffusion of anisotropically phase-segregated Pd/γ-Fe2O3 nanoparticles, where both the hard (fct-FePd) and soft (α-Fe) phases were controlled at the nanometer scale . The HRTEM measurement and magnetic property of the resulting product revealed the existence of an effective exchange coupling between the hard and soft phases. T. Teranishi, Small 2006, 2, 596.  T. Teranishi, Y. Inoue, M. Nakaya, Y. Oumi and T. Sano, J. Am. Chem. Soc. 2004, 126, 9915. T. Teranishi, M. Saruyama, M. Nakaya and M. Kanehara, Angew. Chem. Int. Ed. 2007, 46, 1713 . T. Teranishi, A. Wachi, M. Kanehara, T. Shoji, N. Sakuma and M. Nakaya, J. Am. Chem. Soc. 2008, 130, 4210.
3:45 PM - CC2.4
Asymmetrically Functionalized Nanoparticles via Polymer Single Crystals.
Bing Li 1 , Bingbing Wang 1 , Christopher Li 1 Show Abstract
1 Materials Sci. & Eng., Drexel University, Philadelphia, Pennsylvania, United States
Nanoparticles (NPs), both in solution and in solid state ensembles, show fascinating optic, electronic and magnetic properties. In particular, Janus NPs, which possess a noncentrosymmetric structure with a single core surrounded by compartmentalized corona, are of great interest because of their unique surface pattern. Since de Gennes coined the Janus concept, a number of Janus “architectures” have been reported, including dendrimers, block copolymer micelles, etc. While a Janus NP possesses two types of surface structures, the Janus concept can be extended to “patchy particles” where multiple “patches” (functional groups) are introduced to the NP surface. Judicious selection of “patches” could lead to directed assembly of NPs into complex structures for targeted applications. Most of the reported works on Janus NPs have been focused on relatively large size particles (with diameters greater than 20 nm) and small molar mass ligands. Despite the extensive efforts in polymer-modified NP research, because of the difficulty of controlling polymer phase separation on NP surface, synthesizing sub-10 nanometer, polymer-modified Janus NPs is challenging. In this presentation, we will demonstrate using the single crystal of thiol-terminated polyethylene oxide (HS-PEO) as the solid substrate to immobilize gold NPs (AuNPs); Polyethylene oxide (PEO) was attached to the selected area of the AuNP surface, leading to “patchy” AuNPs. This approach is referred as a “solid state grafting-to” method where polymer single crystals are used as the substrates. Furthermore, we will demonstrate synthesizing Janus AuNPs that are functionalized with two different types of polymer chains on the opposite sides of the AuNP by combining “solid state grafting-to” and “grafting-from” methods. Janus AuNPs with two types of different polymer chains decorated on the opposite sides of the NPs, i.e. amphiphilic PEO-Au-PMMA, PEO-Au-PtBA and hydrophilic PEO-Au-PAA have been synthesized. The Janus nature was clearly demonstrated using a PtNP-decoration method. Using polymer single crystals as the reaction substrates is advantageous because they afford higher throughput compared to self-assembled monolayers. Dissolution of the single crystal also leads to NPs with defined polymer patches. We anticipate that our approach could serve as a generic method for synthesizing polymer-functionalized Janus NPs and this unique system holds promises for achieving controlled assembly and tunable optic and electronic properties of NPs.
4:30 PM - **CC2.5
Quality of Orientational Order Resulting from Self- and field-assisted Assembly of Anisometric Colloids.
Michael Solomon 1 Show Abstract
1 , University of Michigan, Ann Arbor, Michigan, United States
Anisotropic colloids have great potential for assembly into unusual phases with liquid crystalline order. However, experimentally, bulk (3D) assemblies with orientational ordered are difficult to achieve with colloids, even for the simple case of anisometric rods; isotropic phases are instead the more common result. Here we explore the possibility of inducing orientational order in anisometric colloidal rods by the process of controlled sedimentation. The particles assembled are fluorescent sterically stabilized poly(methyl methacrylate) colloids with aspect ratios in the range 3-10. Local orientational order is quantified in 3D by direct visualization with confocal microscopy. The quality of the colloidal liquid crystals produced is studied as a function of rod aspect ratio, applied field strength and attractive interactions between the particles. The relative contributions of thermodynamically driven self-assembly and guided, field-assisted assembly to the observed order are discussed.
5:00 PM - CC2.6
Fabrication, Field Assembly, and Molecular Modification of Patchy Particles.
Ilona Kretzschmar 1 Show Abstract
1 Chemical Engineering, City College of New York, New York, New York, United States
5:15 PM - CC2.7
Stable Colloidal Molecules Formed by Patchy Particles.
Andrey Shalkevich 1 , Frank Scheffold 1 , Peter Schurtenberger 2 Show Abstract
1 Department of Physics, University of Fribourg, Fribourg Switzerland, 2 Adolphe Merkle Institute, University of Fribourg , Fribourg Switzerland
5:30 PM - CC2.8
Fabrication of Novel Magnetic Janus Microparticles.
Amro Dyab 1 , Vesselin Paunov 1 Show Abstract
1 Department of Chemistry, University of Hull, Hull, North Humberside, United Kingdom
We have created a novel type of composite magnetic Janus microparticles which consist of a polymeric matrix containing magnetite nanoparticles that are orientated predominantly in one direction. A dispersion of such anisotropic microparticles in this configuration corresponds to a dispersion of micromagnets. At present there is a considerable interest in fabrication of microparticles which can be manipulated and orientated by application of external electrical or magnetic fields. Such magnetically anisotropic polymeric particles can be easily prepared and their size, morphology and surface groups can be varied in the broad range. Therefore, incorporation of magnetite nanoparticles (Fe3O4) in polymeric matrix to form anisotropic microparticles can provide interesting new applications in different technologies. We report a novel technique for fabrication of magnetically polarized Janus microparticles based on 'arresting' the orientation of oleic acid-coated magnetite nanoparticles (OCMNs) incorporated within the oil phase of oil-in-water (o/w)magnetic emulsion drops. The latter has been achieved by polymerizing of the emulsion droplets in a gelled continuous aqueous phase in the presence of external magnetic filed. The resulting Janus microparticles exhibited very unusual aggregation behaviour and chain structure when exposed to external magnetic field where the magnetic halves of neighbouring microparticles align together. The magnetic properties of the magnetic Janus microparticles were investigated and compared to control samples produced in the absence of external magnetic field. Our results showed that the produced microparticles retain remnance magnetisation with high coercivity indicative of ferromagnetic behaviour as revealed from the magnetization-applied field curve. In addition, similar microparticles, but larger in size, have been prepared without using surfactants and the effect of pH of continuous aqueous phase on the morphology of these microparticles was investigated. This allowed us to fabricate "Pickering-Janus" particles where the magnetic nanoparticles are segregated only on one part of the microparticle surface. We have also extended the same procedure to prepare submicrometer magnetic Janus particles and will report our results on their physical and magnetic properties, self-assembly and aggregation in an external magnetic field.
5:45 PM - CC2.9
``Patch" Functionalized Living Immune Cells.
Albert Swiston 1 , Connie Cheng 1 , Soong Ho Um 1 2 , Darrell Irvine 1 2 , Robert Cohen 3 , Michael Rubner 1 Show Abstract
1 Materials Science and Engineering, MIT, Cambridge, Massachusetts, United States, 2 Biological Engineering, MIT, Cambridge, Massachusetts, United States, 3 Chemical Engineering, MIT, Cambridge, Massachusetts, United States
Tuesday 12/2Transferred Poster CC3.22 to CC2.9 @ 4:45 PM"Patch" Functionalized Living Immune Cells. Albert Swiston
CC3: Poster Session
Wednesday AM, December 03, 2008
Exhibition Hall D (Hynes)
9:00 PM - CC3.1
Fabrication and Self-Assembly of Anisotropic Patchy Particles.
Adam DeConinck 1 2 , Robert Shepherd 1 2 , Jennifer Lewis 1 2 Show Abstract
1 Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 2 Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Colloidal particles that possess both chemical and geometric anisotropy have been shown through simulation  to self-assemble into complex mesoscopic structures. Unlike their isotropic counterparts, anisotropic building blocks can adopt a wide range of self-assembled architectures. Here, we fabricate polymeric microparticles with distinct hydrophilic and hydrophobic patches via stop-flow lithography , in which photopolymerizable liquids are co-flowed through a microfluidic device and then exposed to ultraviolet light through a mask that defines the particle shape. We have created biphasic "Janus" rods as well as structures with two or more equally-spaced patches. Using confocal and fluorescence microscopy, we have directly observed their self-assembly in polar and nonpolar solvents. By tuning the particle composition, shape, and number and location of chemically distinct “patches”, we demonstrate a range of possible mesoscopic structures that can be produced through this approach. S. C. Glotzer and M. J. Solomon. Nat. Mater. 6, 557-562 (2007). D. Dendukuri, S. S. Gu, D. C. Pregibon, T. A. Hatton and P. S. Doyle. Lab Chip 7, 818-828 (2007).
9:00 PM - CC3.11
Integrative Chemistry Toward Designing Polyvinyl Alcohol/Poly-aniline/Vanadium Oxide Nanocomposite-based Macroscopic Fibers: 1D-Highly Sensitive Alcohol Sensors Bearing Enhanced Toughness.
Nicolas Brun 1 2 , Julien Dexmer 1 , Celine Leroy 1 , Helene Serier 1 , Nathalie Steunou 3 , Marie-France Achard 1 , Jacques Livage 3 , Renal Backov 1 Show Abstract
1 , Centre de Recherche Paul Pascal UPR 8641 CNRS, PESSAC France, 2 , Institut des Sciences Moléculaires UMR 5255 CNRS Université Bordeaux 1, TALENCE France, 3 , Laboratoire de Chimie de la Matière Condensée de Paris UMR 7574 CNRS Université Pierre et Marie Curie, PARIS France
9:00 PM - CC3.12
Fabrication of Crosslinked Morphologies of Crosslinked Block Copolymer Nanoparticles Using Cold Vulcanization.
Sungwon Ma 1 , Yonathan Thio 1 Show Abstract
1 Polymer, Textile and Fiber Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
The aim of this study is to understand the crosslinked system of poly(styrene)-b-poly(isoprene) copolymer using cold vulcanization process as a facile method to produce anisometric nanoparticles. The morphologies of block copolymers could be controlled by the type of monomers, block junction, composition, and block size. A systematic methodology, utilizing cylindrical, lamellar, and sphere morphologies of PS-b-PI copolymer, was used for producing fiber, sheet, and ball shaped nanoparticles. The cold vulcanization process was accomplished using sulfur monochloride (S2Cl2) as crosslinking agent. In addition, crosslinking density was investigated by varying exposure times of S2Cl2 at room temperature. The diameter of the nanofibers was almost 50 nm whereas their length was controlled by ultrasonication. The crosslinking density was studied at various crosslinking times but at constant wt% of crosslinking agent for nanofibers and nanosheets. The microstructures and crosslinking density of crosslinked PS-b-PI copolymers were imaged and characterized. This study demonstrated the crosslinking of microphase separated block copolymer as a method to create particles with controlled size, shape, and physical properties.
9:00 PM - CC3.13
Patchy and Anisometric Particles Synthesized by a Dry Aerosol Method.
Bing Guo 1 , Hoon Yim 1 Show Abstract
1 Department of Mechanical Engineering, Texas A&M University, College Station, Texas, United States
A dry aerosol method was used to synthesize anisometric Fe2O3/SiO2 particles. The product particles have segregated gamma-Fe2O3 and amorphous SiO2 phases. Depending on the synthesis conditions, the phase segregation is self-organized into either a core-shell structure, or a half-half structure. In both cases the particles have an overall spherical shape. The particles are characterized by TEM, XRD, fluorescence spectroscopy, Mossbauer spectroscopy and magnetization measurement. These particles have the potential to be used in targeted drug delivery, imaging contrast enhancement, hyperthermia therapy, or biochemical sensing.
9:00 PM - CC3.14
The Role of Condensation in Pseudomorphic Transformations of Silica Spheres.
Won Cheol Yoo 1 , Andreas Stein 1 Show Abstract
1 chemistry, U of Minnesota, MInneapolis, Minnesota, United States
Pseudomorphic transformations are reactions in which the shape of a solid material is preserved. By using a pseudomorphic transformation, it is possible to convert nonporous, amorphous silica spheres to mesoporous silica spheres while retaining the size and monodispersity of the original silica spheres. In this work, we study the role of condensation of silica spheres in different solvents (ethanol, isopropanol and butanol) during surfactant-induced pseudomorphic transformations. Slightly different degrees of condensation cause significant changes in surface morphologies under specific conditions. The pseudomorphic product using parent silica spheres synthesized under ethanol shows a smooth surface but the pseudomorphic products from silica spheres produced under isopropanol and butanol show corrugated surfaces. In both cases, mesopores are formed within the spheres. This significant change in surface morphology after the pseudomorphic transformation is mainly caused by different degrees of condensation in parent silica spheres produced under different solvent conditions because the dissolution and assembly of the silica structure and the surfactant occur at the same time. The degree of condensation was characterized by 29Si solid-state magic angle spinning NMR spectroscopy, and morphological changes were identified using scanning electron microscope and transmission electron microscope techniques. The porosity of the mesoporous silica spheres produced by the pseudomorphic reactions was determined by BET nitrogen sorption measurements and small-angle x-ray scattering. Furthermore, the diffusion depth of the surfactant (cetyl trimethylammonium bromide) was investigated by nanocasting carbon into the mesoporous silica spheres using a phenol-formaldehyde gas phase polymerization and subsequently removing the silica structure. Replicated mesoporous carbon shows a corrugated mesoporous shell and a hollow inside due to the limited diffusion of surfactant into the core of amorphorous silica spheres for isopropanol and butanol as solvents. This transformation could suggest a way to produce mesoporous structures with porous shells and dense cores from amorphous silica with well controlled size and monodispersity. Furthermore, it is another way to synthesize hollow carbon spheres with a mesoporous shell structure.
9:00 PM - CC3.15
Hydrothermal Synthesis of Zeolite Partices in Massively Parallel 3-D Ordered Macroporous (3DOM) Nanoreactors.
Won Cheol Yoo 1 , Sandeep Kumar 2 , R. Lee Penn 1 , Michael Tsapatsis 2 , Andreas Stein 1 Show Abstract
1 Chemistry, University of Minnesota, Minneapolis, Minnesota, United States, 2 Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota, United States
For advanced applications of zeolites, including thin, defect-free catalytic membranes with high efficiencies, growth and aggregation of zeolite nanoparticles must be controlled to obtain monodisperse zeolite particles with desired sizes. To this effect, we have investigated the concept of zeolite growth within massively parallel arrays of "nanoreactors" with sub-100 nm interconnections that can prevent transport of solid products but still provide access to precursors into each nanoreactor. Three-dimensionally ordered macroporous (3DOM) carbon can act as massively parallel reaction chambers for either high yield hydrothermal syntheses or combinatorial syntheses of zeolite particles with uniform sizes (here, silicalite-1), where the product morphology is controlled not only by the shape of the macropores, but also by several parameters (surface chemistry of the nanoreactors, the precursor concentration which determines nucleation processes, the number of infiltration steps, the pore position in terms of depth profile of a 3DOM carbon monolith and the dimensions of windows that connect adjacent pores and define transport properties). Depending on the reactor and processing parameters, the products can be uniform, geode-like, hollow zeolite spheres or high aspect ratio zeolite needles. Furthermore, surface morphologies, ranging from corrugated to smooth surfaces, can be dictated by confinement effects arising from the nanoreactors. Such particles with controllable shapes and defined dimensions are of great interest for preparations of zeolite membranes or for hierarchically structured zeolite catalysts. This nanoreactor engineering approach promises to bring improved control over the morphology of materials prepared by confined syntheses, and the design principles should also be applicable to hydrothermal syntheses of other materials.
9:00 PM - CC3.16
Asymmetric Nanopattern Formation from Elastic, Ionic Lattices Wrapped Around Nanofibers.
Kevin Kohlstedt 1 2 , Graziano Vernizzi 1 , Monica Olvera de la Cruz 1 2 Show Abstract
1 Materials Science and Engineering, Northwestern University, Evanston, Illinois, United States, 2 Chemical and Biological Engineering, Northwestern University, Evanston, Illinois, United States
We show how asymmetric structures can arise on the surface of nanoscale fibers that are covered by a triangular ionic lattice. A model of positive and negative charges tiled around cylindrical nanostructures is introduced, and the effect of competing electrostatic and short-range strain interactions is analyzed. Long-range interactions are modeled by a Coulomb potential between the charges on the lattice, and the lattice strain energies are introduced with interconnected springs between neighboring ions on the cylinder. We determine the optimal orientation of the ionic lattice with respect to the axis of the cylinder, and we compute the effects of the nanofiber curvature. If strain energies are sufficiently large, then chiral lattices are energetically favorable when there is an electrostatic component. Further, the model shows how electrostatic or strain interactions alone cannot give the nanofiber the property of chirality. We analyze also how our findings on ionic lattice symmetries depend on the stoichiometric ratio of the ionic lattice from the 2:1 to 3:1 ratio.
9:00 PM - CC3.17
Microstructural Characterization of Colloid-Derived Bimetallic Pd-Cu Nanocatalysts Supported on γ-Al2O3.
Zhenyu Liu 1 , Kathryn Guy 2 , John Shapley 2 , Charles Werth 3 , Qi Wang 4 , Anatoly Frenkel 4 , Judith Yang 1 Show Abstract
1 Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, Pennsylvania, United States, 2 Department of Chemistry and Center of Advanced Materials for the Purification of Water with Systems, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 3 Department of Civil and Environmental Engineering and Center of Advanced Materials for Purification of Water with Systems, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 4 Physics Department, Yeshiva University, New York, New York, United States
9:00 PM - CC3.18
Non-linear Dependence of Interfacial Energy on Monolayer Structure of Striated Nanoparticles.
Jeffrey Kuna 1 , Kislon Voitchovsky 1 , Steve Mwenifumbo 2 , Molly Stevens 2 , Francesco Stellacci 1 Show Abstract
1 Department of Materials Science and Engineering, MIT, Cambridge, Massachusetts, United States, 2 Department of Materials, Imperial College, London United Kingdom
9:00 PM - CC3.19
Colloidal Thin Film Growth on a Micro-fabricated Substrate.
Rajesh Ganapathy 1 , Mark Buckley 1 , Itai Cohen 1 Show Abstract
1 Physics, Cornell University, Ithaca, New York, United States
9:00 PM - CC3.2
Dielectrophoretically-Driven Alignment of Unique Anisotropic Polymer Particles.
Kevin Herlihy 1 , Janine Nunes 1 , Joseph DeSimone 1 2 Show Abstract
1 Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States, 2 Chemical Engineering, North Carolina State University, Raleigh, North Carolina, United States
Four sets of unique, highly anisotropic polymer particles were synthesized utilizing the Particle Replication in Non-wetting Templates (PRINT) process. The four sets consisted of rods, discs, fenestrated hexagons, and boomerang-shaped particles. These monodisperse, micron-sized particles were composed of mainly poly(ethylene glycol) triacrylate. The particles were aligned using dielectrophoresis, a technique known to drive the assembly of colloidal systems. Particle alignment and particle chaining were observed in aqueous suspensions using moderate electric fields and frequencies (20-40 V AC, 0.5 – 5.0 kHz). In most cases, the particles aligned with their longest axis parallel to the electric field. Hexnut and disc shaped particles assembled into hexagonal close packed lattices, and the rod particles exhibited rectangular packing. Due to the size and geometry of the boomerang particles, limited chaining was observed, however the field triggered a change from random to more ordered packing arrangement.
9:00 PM - CC3.20
Coordinated Sub-micron Spheres: A New Self-assembling Building Block.
Hyunchul Kim 1 , Hyunjung Shin 1 , Changdeuck Bae 1 Show Abstract
1 National Research Lab for Nanotubular Structures of Oxides, Center for Materials and Processes of Self-Assembly, and School of Advanced Materials Engineering, Kookmin University, Seoul Korea (the Republic of)
A fabrication method and the self-assembly of “patch” colloidal building blocks (which we call them “coordinated particles”) are presented. By using contact area lithography with site-selective growth (Bae et al, J. Am. Chem. Soc. 2007, 129, 14232), nanometric surface chemical contrasts were realized by coating surfaces with self-assembled monolayers (SAMs) except the contact area either between colloidal particles or between colloids and substrate. Nanoscale site-specific heterogeneous nucleation and growth of oxide materials of titanium were studied using the patterns of SAMs onto the curved surfaces of silica. Experimental results suggest that a combination of the large difference in the surface energy between the growing and surrounding surfaces and the diffusion-controlled growth leads to complete nanoscale site-specificity. We successfully fabricated the coordinated particles consisting of silica spheres and hemispheres of titania of the spheres’ coordination numbers. We discuss how the patch particles can be grown and self-assembled each other in a controlled manner.
9:00 PM - CC3.21
The Isotropic-Nematic Interface in Suspensions of Na-Fluorohectorite Synthetic Clay.
Henrik Hemmen 1 , Nils Ringdal 1 , Eduardo de Azevedo 2 , Elisabeth Hansen 1 , Yves Méheust 3 , Jon Fossum 1 , Mario Engelsberg 4 , Kenneth Knudsen 5 Show Abstract
1 Department of Physics, Norwegian University of Science and Technology, Trondheim Norway, 2 Programa de Pós-Graduação em Ciência de Materias, Universidade Federal de Pernambuco, Recife Brazil, 3 Geosciences Rennes, Université de Rennes 1, Rennes France, 4 Departamento de Física, Universidade Federal de Pernambuco, Recife Brazil, 5 Physics Department, Insitute for Energy Technology, Kjeller Norway
Colloidal suspensions of the platelet-shaped anisometric synthetic clay Na-fluorohectorite (NaFh) in saline water exhibit coexisting isotropic and nematic phases, due to gravitational separation and ordering of the polydisperse particles. We study this ordering of the NaFh platelets near the isotropic-nematic interface, where a sharp horizontal layer appears. We utilize three complimentary experimental techniques: Visual observation of birefringence, Magnetic Resonance Imaging and synchrotron Wide Angle X-ray Scattering. We find that the particles are lying horizontally, i.e. with the mean particle director along the vertical direction, which is perpendicular to the isotropic-nematic interface. We also observe frustration effects due to competition between nematic ordering and homeotropic ordering of the clay particles anchored to the container glass walls, and/or due to alignment in an external magnetic field (Freederikz transition).
9:00 PM - CC3.3
Synthesis and Characterization of CdPd Sulfide Heterostructured Nanoparticles.
Masaki Saruyama 1 , Masayuki Kanehara 1 , Toshiharu Teranishi 1 Show Abstract
1 Department of Chemistry, Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki, Japan
Combination of distinct metal chalcogenide nanoparticles would have great potential for various applications, including biological labeling, light-emitting diodes, and photovoltaic devices. They may also serve as building blocks for complex nanostructures in nanodevices. Recently, we reported anisotropically phase-segregated nanoparticles consisted of Co9S8 and PdSx (CoPd sulfide nanoparticles)., On the basis of our proposed mechanism for the formation of CoPd sulfide nanoparticles in which the crystalline Co9S8 phases anisotropically grow on the amorphous PdSx seed nanoparticles, the PdSx phases are the key material for the formation of heterostructures. In order to extend the kind of sulfide seeds for the designed synthesis of anisotropically phase-segregated nanoparticles, herein we report on the synthesis of CdPd sulfide heterostructured nanoparticles by the PdSx- and CdS-seeded growth methods. In the PdSx-seeded growth reaction, the amorphous PdSx seed nanoparticles of 5.4±0.8 nm in size were reacted with the mixture containing Cd(acac)2 and 1-octadecanethiol (C18SH) at 260 °C for 120 min to form the flower-like CdPd sulfide heterostructured nanoparticles (nanoflowers). TEM observation revealed that the nanoflowers had the faceted PdxCdyS cores of 6 nm and the radial length of CdS petals of 3 nm in size, clearly indicating the nucleation of CdS on the PdxCdyS core. Size of PdxCdyS core is similar to that of PdSx seeds. High-resolution TEM observation revealed that the CdS phases possessed zincblende structure with a minor wurtzite structure. It is quite interesting that the crystal structure transformation from amorphous PdSx seeds to crystalline PdxCdyS phases is induced by the diffusion of Cd2+ ions into PdSx seeds (cf., the diffusion of Co2+ ions does not occur), and S2- ions simultaneously diffuse from the PdSx seeds to the outside to form the CdS phases. Then the reaction of the nearly spherical CdS seed-nanoparticles (~9.7 nm) with Pd(acac)2 and C18SH at 260 °C for 180 min predominantly gave the dumbbell-shaped CdS/PdxCdyS/CdS nanoparticles (nanodumbbells) with two CdS phases connected by PdxCdyS phase. It was found from TEM observation, more than 80 % of nanoparticles had a dumbbell-shape, and the average size was 20 nm (length) × 10 nm (width). From the investigation of formation mechanism of nanodumbbells, we revealed that the dumbbell-structures were generated by fusing two CdS/PdxCdyS nanoparticle dimers, as observed in the formation of PdSx/Co9S8/PdSx nanopeanuts. By utilizing this formation mechanism, the self-assembly of CdS nanorods was carried out via binding CdS nanorods with PdxCdyS phases. The PdxCdyS grew preferentially on the tips of CdS nanorods and fused to link nanorods, resulting in the formation of one-dimentional wires.ReferencesT. Teranishi et al., J. Am. Chem. Soc. 2004, 126, 9914.T. Teranishi, M. Saruyama et al., Angew. Chem. Int. Ed. 2007, 46, 1713.
9:00 PM - CC3.4
Superparamagnetic Composite Colloids with Anisotropic Structures.
Yadong Yin 1 , Jianping Ge 1 , Yongxing Hu 1 Show Abstract
1 Chemistry, University of California, Riverside, California, United States
We report the synthesis and assembly of superparamagnetic magnetite-polystyrene composite colloids with anisotropic structures. Magnetite colloidal nanostructures were first synthesized using a high-temperature hydrolysis process, and then used as seeds for the subsequent emulsion polymerization process. By controlling the interfacial tension between the seeds and the monomers, and the swelling and phase separation of the monomer in the growing polymer shell, we are able to produce magnetite-polystyrene composite particles with various geometric shapes, including isotropic core-shell spheres, anisotropic core-shell spheres, doublets and rods. The anisotropic structures show dramatically different self-assembly behavior than isotropic structures when they are subjected to an external magnetic field, producing unusual structures such as zig-zag chains. These colloidal composite particles, with superparamagnetic property and anisotropic structures, would allow a wide range of potential applications, for example, as active components for biosensors and building blocks for photonic bandgap materials.
9:00 PM - CC3.6
Functionalized Biodegradable Multiphasic Microparticles and Microfibers via Electrified Jetting for Biomedical Applications.
Srijanani Bhaskar 1 , Kyung Ho Roh 1 , Xuwei Jiang 4 , Kelly Marie Pollock 5 , Mutsumi Yoshida 4 , Suparna Mandal 4 , Jonathan Hitt 4 , Gregory Baker 2 , Joerg Lahann 1 4 3 Show Abstract
1 Macromolecular Science and Engineering, University of Michigan, Ann Arbor, Michigan, United States, 4 Chemical Engineering, University of Michigan, Ann Arbor, Michigan, United States, 5 Chemical Engineering, Cornell University, Ithaca, New York, United States, 2 Chemistry, Michigan State University, Lansing, Michigan, United States, 3 Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan, United States
Precise control of nano- and microscale architecture of biomedical devices is desirable for their improved performance. Using side-by side electrified co-jetting process , we have fabricated biodegradable biphasic microparticles with polymer solutions prepared from commercially available poly(lactic-co-glycolic acid). By varying different solution and electrohydrodynamic processing parameters, the complex fluid dynamics of such organic polymer solutions at the tip of the Taylor cone formed during jetting resulted in a variety of non-equilibrium biphasic shapes, such as discs and rods, in addition to spheres. This precise control over particle shape and anisotropy provides multifunctionality not achievable with their isotropic counterparts. Hemisphere-specific surface modification of these particles was achieved through introduction of free acetylene groups in one hemisphere of the biphasic microparticles, followed by selective immobilization of polyethylene glycol onto this hemisphere via “click chemistry”. Similarly, biphasic particles modified to present biotin only on one hemisphere were capable of self-assembling into dimers, trimers, and tetramers in the presence of streptavidin, demonstrating their multifunctionality. Interestingly, extension of electrified co-jetting process for the formation of fibers resulted in biphasic fibers with aligned phases. These biphasic microparticles and fibers may have potential applications in multiplexed bioassays and tissue engineering scaffolds capable of simultaneously supporting the controlled growth of multiple cell lines.1.Roh KH, Martin DC, Lahann J. Nat Mater. 2005 Oct;4(10):759-63.
9:00 PM - CC3.7
Rippled Domain Nanoparticles as Catalytic Platforms for Organic Chemistry.
Benjamin Wunsch 1 , Francesco Stellacci 1 Show Abstract
1 Department of Materials Science and Engineering, MIT, Cambridge, Massachusetts, United States
Nanoparticles with unique, phase-segregated domains – termed rippled domains - can be generated by using two different ligands to synthesize the particle. Ripple domainscan modify the physical and chemical properties of the particle, suggesting changes in the molecular structure of the domains can affect the surface energy of the particleinterface. From this we have initiated work to see if organic catalysts, embedded in the ripple domains, are affected by these changes in the molecular structure. Preliminary work with these catalytic platforms has shown that a model catalytic ester hydrolysis can be modulated or enhanced depending on the presence of the ripple domain structure.
9:00 PM - CC3.8
Complex Au-Ag-Pt Nanostructures: Colloidal Strategies to Optimize the Heterostructure for Optical and Catalytic Performance.
Kyoungweon Park 1 , Hilmar Koerner 1 , Joseph Slocik 1 , Richard Vaia 1 , Michael Jespersen 1 , Rajesh Naik 1 Show Abstract
1 , Air Force Research Laboratory, Wright-Patterson AFB, Ohio, United States
Multicomponent nanostructures have great potential in a wide range of applications due to their unique chemical, optical, and magnetic properties that arise from the structural and compositional complexity and associated heterojuctions. In this study, robust, efficient and scalable synthesis of structurally and compositionally complex metal (Pt, Au and Ag) nanostructures is discussed. Building upon previous findings that elucidated the role of binary surfactant mixtures, pH and reductant concentration on the re-initiation of gold nanorod growth only from the rod terminus, secondary chemical reduction and galvanic exchange reactions are adopted to introduce additional metal (Ag and Pt) at various locations around the gold nanorod template. Depending on interfacial strain, facet-dependent chemical reactivity, pH and the oxidation state and reduction potential of the metal precursor, the structure of the second component can be tuned from a continuous shell to islands, resulting in heterostructures ranging from onion-like to raspberry-like. Furthermore, the location of the secondary deposition can be modulated by masking one surface of the nanorod template, resulting in asymmetric nanostructures. The effect of the structural and compositional complexity on the optical and catalytic properties is discussed with regards to the different heterojuctions formed on the nanoparticles. For example, the formation of Ag shell around Au NR with high aspect ratio (~7) induces huge surface plasmon blue shifts (both longitudinal and transverse) and enhances electromagnetic field around the structure. The solution color changes dramatically due to the hybrid surface plasmon appearing around 400nm. The deposition mode of Pt on the Au-Ag core shell structure and the degree galvanic replacement further modifies the surface plasmon and local electromagnetic field distribution. Also, structural details of the Au/Ag/Pt trimetallic nanostrutures alters the catalytic efficacy, as demonstrated via the hydrogenation reaction of unsaturated alcohol. The advantage of the presented colloidal approach is the ability to provide finely-tailored, and narrowly-dispersed nanostructures, either for specific sensing, catalysis, or electrochemical applications; as building blocks for self-assembled mesostructures; or to provide model materials to forward the fundamental understanding of structure-function relationships.
9:00 PM - CC3.9
Catalytically Driven Movement of Bimetallic Colloidal Particles.
Yang Wang 1 , Timothy Kline 1 , Michael Ibele 1 , Shih-to Fei 1 , Darrell Velegol 2 , Ayusman Sen 1 , Thomas Mallouk 1 Show Abstract
1 Chemistry, Pennsylvania State University, University Park, Pennsylvania, United States, 2 Chemical Engineering, Pennsylvania State University, University Park, Pennsylvania, United States
Self-propulsion and directed movement of nano- and micro-particles can in principle provide novel components for applications in microrobotics and MEMS. Our research involves the design of catalytic propulsion systems and the control of colloidal movement based on this principle. We have designed autonomous nanomotors and micropumps that mimic biological motors by using catalytic reactions to generate forces derived from chemical gradients. By studying the electrochemical reactions of hydrogen peroxide at ultramicroelectrodes, we have developed an approach to understanding the principles of catalytically driven motion. The results provide strong support for a bipolar electrochemical mechanism, which allows us to predict the behavior of bimetallic motor systems. Based on these principles, we are able to rationalize the formation of ring patterns in silica colloidal suspensions due to fluid flow induced by immobilized catalytic pumps. Through architectural control of bimetallic catalytic particles, we have recently developed systems that undergo more complex movement. For example, we have constructed 10-micron scale linear or rotary motors by contact lithography. In these chiral motors, bimetallic Au-Pt patterns are either free-standing or supported on an organic resist layer. The potential for elaboration of these designs to more complex nanomachine assemblies will be discussed.
Erik Luijten University of Illinois, Urbana-Champaign
Sharon C. Glotzer University of Michigan-Ann Arbor
Francesco Sciortino Universitá di Roma “La Sapienza”
CC4: Theory and Simulation of Self-Assembly
Wednesday AM, December 03, 2008
Fairfax A (Sheraton)
9:30 AM - **CC4.1
Computer Simulations of the Self-assembly and Crystallization of Patchy Particles.
Jonathan Doye 1 Show Abstract
1 Department of Chemistry, University of Oxford, Oxford United Kingdom
In this contribution I will provide an overview of the computational work of my group aimed at understanding the design rules for the self-assembly and crystallization of patchy particles. In particular, we are interested how the nature of the interactions (e.g. the geometry of the patch positions, and their strength and width) can be used to control their assembly behaviour, and hence to form novel materials.Firstly, we consider the self-assembly of shell-like clusters made up of a specific number of particles and with a high-symmetry structure . We have delineated the regions of parameters space where this monodisperse self-assembly is successful, and have shown how this reflects the requirements for both thermodynamic stability and kinetic accessibility. We find that for simpler target structures, self-assembly is robust and relatively straightforward, but that as one more considers more complex targets, assembly becomes increasingly difficult, unless one introduces a torsional component to the interactions to reduce the number of ways that the system can become trapped in incorrectly-assembled structures. Secondly, we explore the crystallization of patchy particles in both two- and three dimensions, and whether their interactions can be tuned to allow the formation of unusual colloidal materials, such as low-dimensional colloidal crystals, including colloidal diamond, and two-dimensional quasicrystals [2,3]. A.W. Wilber, J.P.K. Doye, A.A. Louis, E.G. Noya, M.A. Miller, P. Wong, Reversible self-assembly of patchy particles into monodisperse icosahedral clusters, J. Chem. Phys. 127, 085106 (2007). J.P.K. Doye, A.A. Louis, I-C. Lin, L.R. Allen, E.G. Noya, A.W. Wilber, H.C. Kok, R. Lyus, Controlling crystallization and its absence: Proteins, colloids and patchy models, Phys. Chem. Chem. Phys. 9, 2197-2205 (2007). E.G. Noya, C. Vega, J.P.K. Doye and A. A. Louis, Phase diagram of model anisotropic particles with octahedral symmetry, J. Chem. Phys. 127, 054501 (2007).
10:00 AM - **CC4.2
How Viral Capsids Adapt to Mismatched Cargoes—identifying Mechanisms of Morphology Control with Simulations.
Michael Hagan 1 Show Abstract
1 Physics, Brandeis University, Waltham , Massachusetts, United States
We develop a computational model that represents the dynamical assembly of viral proteins into capsids with icosahedral symmetry both in the presence and absence of functionalized nanoparticles. We find parameter values for which subunits faithfully form empty capsids with a single morphology, but adaptively assemble into different icosahedral morphologies around nanoparticles with different diameters, as seen in recent experiments. We find that adaptation is only successful at moderate nanoparticle-subunit interaction strengths; with strong interactions assembly is frustrated by metastable partial capsids whose curvature is incommensurate with the nanoparticle geometry. We compare the simulation results to recent experiments in which brome mosaic virus capsid proteins assemble around functionalized nanoparticles, and suggest future experiments motivated by model predictions. Finally, we discuss implications of these results for the development of nanostructured materials with controlled and adaptable sizes.
10:30 AM - **CC4.3
Icosahedral Ionic Shells.
Graziano Vernizzi 1 , Monica Olvera de la Cruz 1 Show Abstract
1 Materials science and engineering, Northwestern University, Evanston , Illinois, United States
11:30 AM - **CC4.4
Kinetic Arrest, Activated Dynamics and Mechanical Response in Suspensions of Anisometric Colloids and Nanoparticles.
Kenneth Schweizer 1 , Galina Yatsenko 1 , Mukta Tripathy 1 , Rui Zhang 1 Show Abstract
1 Department of Materials Science, University of Illinois, Urbana, Illinois, United States
Slow dynamics in suspensions of nonspherical particles under quiescent and mechanically-driven conditions is a problem of major scientific and materials engineering importance. A fundamental question is how excluded volume forces, strong short range interparticle attractions, and colloid shape determine kinetic arrest and mechanical properties. Besides its intrinsic interest, understanding the emergence of nonequilibrium amorphous states (glass, gel) is critical for both the practical realization of possible new equilibrium crystal structures of anisometric colloids and the control of flow-driven printing of highly concentrated particle inks. We have developed a microscopic theory for the glassy translational dynamics of anisometric particles which includes thermally activated barrier hopping. Suspensions of hard core diatomic, triatomic and spherocylinder objects exhibit ideal kinetic arrest boundaries that are nonmonotonic functions of aspect ratio. Rather remarkably, the kinetic arrest boundaries closely resemble the jamming analogs of granular ellipsoids and spherocylinders. A strict nonergodicity transition is avoided below random close packing due to noise-induced activated barrier hopping. The consequences of particle shape anisotropy on the entropic barrier height, alpha relaxation time, shear modulus, and yielding behavior have been determined. Based on analytic arguments, we find that many properties for different aspect ratios and volume fractions collapse well onto master curves based on a local fluid structural variable that quantifies mean square forces. Generalization of the theory to treat coupled translational and rotational single particle motion has been achieved based on the concept of a two-dimensional dynamical free energy landscape. A plastic amorphous solid state is predicted in addition to a fully localized ideal glass state. The basic approach has also been applied to treat the slow dynamics and shear modulus of more complex rigid objects of one (rods, rings), two (planar disks) and three (e.g. cubes, octadechedron, tetrahedron) dimensional character. In the presence of short range attractions, vitrification competes with gelation, and a shape-dependent re-entrant glass-fluid-gel behavior is predicted at high volume fractions. A unified understanding of how barriers and relaxation times in gel-like systems depend on local structure, attraction strength and volume fraction has been achieved within the same collisional framework established for repulsion-dominated glassy materials. Generalization of the theoretical methods to treat chemically patchy nonspherical colloids is underway. This work is supported by DOE-BES via the Frederick Seitz Materials Research Laboratory.
12:00 PM - CC4.5
Functionalized Particles with Low Valence. Numerical and Theoretical Predictions.
Francesco Sciortino 1 Show Abstract
1 , Universita' La Sapienza, Roma Italy
I will review some problems concerning the phase diagram, the self-assembly and the gelation of patchy particles which can form a limited number (valence) of attractive interactions.In the talk I will show that for a nontrivial self-assembly phenomenon, originating branched loop-lessclusters, it is possible to derive a fully predictive parameter-free theory of equilibrium self-assembly bycombining the Wertheim theory for associating liquids with the Flory-Stockmayer approach for chemicalgelation[1-3]. I will also address some connections between physical and chemical gels.I will also discuss the self-assembly of a simple model for four single strands of DNAtethered to a central core, and show that the model exhibits a rich phasediagram that includes at least four thermodynamically distinctamorphous phases (polyamorphism) in a one-component system.The dense phases consist of a hierarchy of interpenetrating networks, reminiscent of awoven cloth [4-5]1] E. Bianchi, J. Largo, P. Tartaglia, E. Zaccarelli, F. Sciortino Phase diagram of patchy colloids: towards empty liquids Phys. Rev. Lett. 97, 168301, 2006 2] Emanuela Bianchi, Piero Tartaglia, Emilia La Nave and Francesco Sciortino Fully Solvable Equilibrium Self-Assembly Process: Fine-Tuning the Clusters Size and the Connectivity in Patchy Particle Systems J. Phys. Chem. B 111, 11765 (2007). 3] F. Sciortino, E. Bianchi, J. Douglas and P. Tartaglia Self-assembly of patchy particles into polymer chains: A parameter-free comparison between Wertheim theory and Monte Carlo simulation J. Chem. Phys.126, 194903, 20074] Largo, J.; Starr, F. W.; Sciortino, F. Self-Assembling DNA Dendrimers: A Numerical Study Langmuir, 23, 5896-5905. 20075] Hsu C., Largo, J., Sciortino, F. Starr, F., A challenge for functionalized nanoparticles: Multiple Liquid-Liquid Critical points (preprint)
12:15 PM - CC4.6
Graphene Sheets-Oil Nanocomposites: Equilibrium and Transport Properties from Molecular Simulation.
Alberto Striolo 1 , Deepthi Konatham 1 Show Abstract
1 School of Chemical Biological and Materials Engineering, University of Oklahoma, Norman, Oklahoma, United States
Nanostructured materials hold unrestricted promises in catalysis, material science and engineering. It has long been thought that dispersing nanoparticles in a polymer blend can enhance both mechanical and transport properties. It would be for example desirable to generate a polymer nanocomposite with high thermal conductivity. Such materials could be obtained by dispersing thermally conductive nanoparticles within polymers. Carbon-based nanoparticles are extremely promising towards these goals, although the use of carbon nanotubes is hindered by high resistance to heat transfer from the nanotubes to the polymer matrix.We are interested in composites in which graphene sheets (GS) are dispersed within organic oils. We observed that pristine GS agglomerate when dispersed in oils such as octane, hexane and dodecane. However, our equilibrium molecular dynamic simulations demonstrate that when the GS are functionalized on their edges with short branched hydrocarbons, they remain well dispersed within the oils for up to 100ns. Because our goal is to control the composite thermal transport by manipulating the GS self-assembly, we are conducting equilibrium and non-equilibrium molecular dynamics simulations to assess the effective interactions between GS dispersed in oils, the self-assembly of GS within oils, the structure of the fluid surrounding the GS, and the heat transfer from a GS to the surrounding matrix. Our tools are designed to understand the effect of GS size, oils molecular weight and molecular architecture on the GS dispersability and GS-oil heat transfer rate. We will discuss our results and how they could be used to design novel polymer nanocomposites.
12:30 PM - CC4.7
Diffuse-Interface Field Approach to Simulation of Self- and Guided-Assembly of Charged Particles of Various Shapes and Sizes.
Paul Millett 1 , Yu Wang 2 Show Abstract
1 , Idaho National Laboratory, Idaho Fall, ID, Idaho, United States, 2 Department of materials science and engineering, Virginia Tech, Blacksburg, Virginia, United States
Recent advances in the ability to experimentally control the size, shape, and composition of nanoparticles have significantly broadened the possibilities to create novel mesoscale structures as a result of their “bottom-up” assembly. A particularly efficient approach to facilitate various assembly dynamics in colloidal systems is to control the collective electrostatic interactions by tuning the particle charge density and/or dipole moment as well as the application of an external electric field. Here, we present a novel mesoscale simulation approach that utilizes diffuse interface fields to capture and investigate the dynamic assembly processes for arbitrarily shaped particles with arbitrary charge density and/or dipole moment. Individual particle positions are updated due to long-range electrostatic forces and torques as well as short-range (steric) repulsive interactions. We will present results illustrating the method’s ability to predict a wide variety of colloidal crystal structures, with a particular focus on binary lattices consisting of positively- and negatively-charged particles. We find that varying the shapes, relative charge density ratio, as well as the relative number density of each particle type results in vastly different assembly dynamics.
12:45 PM - CC4.8
Multivalent Nanoparticles: Adsorption and Organization of Bidisperse Polymer Chains onto a Solid Interface.
Folusho Oyerokun 1 , Richard Vaia 1 , John Maguire 1 , Barry Farmer 1 Show Abstract
1 Nanostructured and biological materials branch, AFRL, Wright-Patterson AFB, Ohio, United States
Multivalent nanoparticles, i.e. nanoparticles with two or more (organic, polymeric or biological) ligands attached to their surfaces, are used in a variety of scientific, biomedical and technological applications. By introduction of different chemical groups orligands of varying size (length mismatch) and elastic properties (flexible, semiflexible or rigid), it is possible to tune magnetic, optical and chemical properties of the nanoparticles. The most common protocols for synthesizing these multivalent nanoparticles involves immersion of the particles into a solution containing the various ligands or into a solution containing an excess of one ligand to drive a partial (solvent mediated) exchange reaction with a previously bound ligand. Despite intense experimental activities, the dependence of the surface coverage (e.g. mole fractions of the respective chains on the nanoparticle) on free ligand concentration and solvent quality is still poorly understood. As an initial step, this study will discuss a theoretical model to address the thermodynamics of adsorption of bidisperse end-functionalized polymer chains in a good solvent onto a flat surface. At equilibrium, the absorbed chains form a bidisperse polymer brush in contact with the solution. Our analysis, based on self consistent field theory, looks at the role of molecular parameters; such as ratio of the polymerization index (i.e. degree of bidispersity), energy gained via absorption of the terminal group, equilibrium surface coverage, brush height and degree of penetration of free short and long chains into the brush layer. The dependence of the composition of the chains of different lengths on grafted surface as a function of their relative composition in the solution and overall concentration will also be discussed. The approach presented here can be generalized to the case of immiscible polymeric ligands, where in addition to conformational entropy; the intersegment repulsive interaction plays an important role in determining the equilibrium properties of the grafted layer.
CC5: Fabrication and Assembly I
Wednesday PM, December 03, 2008
Fairfax A (Sheraton)
2:30 PM - **CC5.1
Shape Controlled Multivalent 3D Particles via Stop Flow Mask and Interference Lithography.
Edwin Thomas 1 , Ji-Hyun Jang 1 , Patrick Doyle 2 Show Abstract
1 Materials Science and Engineering, MIT, Cambridge, Massachusetts, United States, 2 Chemical Engineering, MIT, Cambridge, Massachusetts, United States
We use standard mask lithography and holographic interference lithography (IL) combined with stop flow lithography (SFL) as an easy and high-throughput fabrication method for creating complex polymer particles with controlled symmetry, size and highly non-convex shapes and fine scale 3d bicontinuous internal structures. IL has already been demonstrated as a promising approach to the fabrication of large-area and periodic 3D structures on the sub-micrometer scale. An advantage of the IL method for fabrication of particles is that a particle supra-structure with a particular point group which is not easily or otherwise accessible can be created by the reassembly of blends of particles with prescribed shapes. This approach can give access to a wider range of structures with novel optical or mechanical properties. IL involves the formation of a time independent spatial variation of intensity created by the interference of two or more beams of light. The pattern that emerges out of the intensity distribution is transferred to a light sensitive medium, such as a photoresist, to yield structures. Importantly by proper choice of beam parameters one can control the geometrical elements and volume fraction of the structures. Multivalent particles are fabricated by creating disconnected IL structures in a negative photoresist. Manipulation of the experimental parameters of intensity, polarization, phase and wave vectors of the interfering beams allows one to target specific space group structures. The use of a small number of beams results in a light intensity distribution with regions of high intensity being concentrated in Wyckoff sites of low multiplicity and high symmetry. The use of a negative photoresist implies a high crosslink density of insoluble polymer in these regions. The valency of the resultant particles is determined by the connectivity of these Wyckoff sites and the process by which they become disconnected. To disconnect the structure, the connecting arms are made thin by decreasing the exposure and by subsequent strong development. The particles can be separated either by chemical etching with UV/ozonolysis or by mechanical forces, for example, from the expansion due to the freezing of water in the continuous matrix region. Use of a standard mask enables well defined prism shaped large scale particles to be defined. Combining this with a phase mask in the microfludic stop flow apparatus, permits such large (eg 50 micron diameter) particles to also contain 3d features at the 200nm scale.
3:00 PM - **CC5.2
Structured Colloids: Clusters, Patchy Colloids & Self Replication.
David Pine 1 Show Abstract
1 , New York University, New York, New York, United States
3:30 PM - CC5.3
Nonspherical Particles: Shape Control and Assembly.
Tao Deng 1 , Yu Du 1 , James Cournoyer 1 , James Schermerhorn 1 , Joleyn Balch 1 , Margaret Blohm 1 Show Abstract
1 Nano Advanced Technology, GE Global Research Center, Niskayuna, New York, United States
Nonspherical particles draw increasing interests due to the impact that these particles bring to the bulk properties of various material systems, such as biological, optical, and mechanical systems. The challenges in the synthesis of nonspherical particles, especially in large quantity, limit the widespread use of such particles in both fundamental studies and industrial applications. This presentation reports a straightforward approach in transforming spherical particles into nonspherical particles using controlled directional chemical reaction. A simple model is proposed to predict the geometry of the resulting nonspherical particles. The shape and dimension of the nonspherical particles generated through such process matched well with the prediction of the model. The particles generated are uniform in size and also with large quantity, which open the door for further studies of their fundamental properties. This presentation will also report the initial observation of the assembly of these nonspherical particles. Dispersed in a solvent, these particles can form ordered layers on substrates through the evaporation assisted assembly. During the assembly of spherical particles with homogeneous surfaces, there is no orientational order in the assembled face centered cubic structure due to their spherical symmetry. In the assembly of these nonspherical particles, however, there are several energy states that are associated with different orientational orders in the packing. These orientaional orders are due to the nonspherical symmetry of the particles. This presentation will discuss the observed orientational orders of the particles and also propose ways of generating other possible packing geometries through manipulation of the assembly forces at different structure forming stages.
3:45 PM - CC5.4
Restricted Dislocation Motion in Crystals of Colloidal Dimer Particles.
Sharon Gerbode 1 , Stephanie Lee 2 , Chekesha Liddell 2 , Itai Cohen 1 Show Abstract
1 Physics, Cornell University, Ithaca, New York, United States, 2 Materials Science and Engineering, Cornell University, Ithaca, New York, United States
The microscopic motion of dislocations plays a crucial role in melting and governs numerous macroscopic phenomena observed in crystalline materials, including plastic flow, yield, and work hardening. Studies of dislocations in colloidal crystals enable direct visualization of such processes. Thus far, such studies have focused on crystals of spherical particles, whose defect transport mechanisms are well described by existing models. Here, we describe nucleation and transport of dislocations in novel colloidal crystals of anisometric, hollow, hard dimer particles with spherical lobes of diameter 1.36 µm and lobe separation 1.46 µm (particle polydispersity < 5%). At high area fractions, monolayers of these particles form a novel ordered structure previously only observed in simulations. In this phase, called a degenerate crystal, the dimer particle lobes occupy triangular lattice sites while the dimer orientations uniformly populate the three lattice directions. We find that geometric constraints dramatically restrict dislocation motion in these structures. In particular, we show that obstacles formed by certain particle orientations severely limit the range over which dislocations can glide. Finally, we observe that longer range transport can proceed beyond such obstacles via dislocation reactions that switch the direction of propagation.
4:30 PM - **CC5.5
Assembly of Finite-size Nano-Clusters via Stepwise Encoding.
Oleg Gang 1 , Mathew Maye 1 , Dmytro Nykypanchuk 1 , Daniel van der Lelie 1 , Marine Cuisinier 1 , Cheng Chi 1 Show Abstract
1 , Brookhaven National Lab, Upton , New York, United States
5:00 PM - CC5.6
The Pair Potential of Hairy Beads: Microspheres Grafted with Filamentous Bacteriophage.
Phil Huang 1 , Seth Fraden 1 , Karim Addas 1 , Andy Ward 1 , Nolan Flynn 2 , Michael Hagan 1 , Zvonimir Dogic 1 Show Abstract
1 Physics, Brandeis University, Waltham, Massachusetts, United States, 2 Chemistry, Wellesley College, Wellesley, Massachusetts, United States
5:15 PM - CC5.7
Nanoscale Patterning of Spherical and Cylindrical Surfactant-Coated Nanoparticles.
Chetana Singh 1 , Sharon Glotzer 1 2 Show Abstract
1 Department of Chemical Engineering, University of Michigan, Ann Arbor, Ann Arbor, Michigan, United States, 2 Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan, United States
We present simulation results of phase separation and pattern formation in binary [1-3] and ternary  self-assembled monolayers (SAMs) of immiscible surfactants on nanoparticle surfaces. We focus on patterns formed on substrates with a high degree of curvature, e.g. nanospheres  and nanotubes , and compare them with patterns formed on flat substrates . Recent experimental results [5, 6] have shown that patterns on nanoparticles can help functionalize them to form nano-building blocks for bottom-up assembly of novel materials. Surface patterns are also important for applications in catalysis, ceramics, photonics etc. Our studies provide a tool to predict and control patterns that form on nanostructured surfaces as a function of tunable thermodynamic and geometric parameters.References:1. C Singh, PK Ghorai, MA Horsch, AM Jackson, RG Larson, F Stellacci and SC Glotzer, “Entropy-mediated patterning of surfactant-coated nanoparticles and surfaces”, Physical Review Letters 99, 226106 (2007).2. C Singh and SC Glotzer, “Patchy vs. striped phase separation of binary self-assembled monolayers”, preprint.3. C Singh and SC Glotzer, “Nanoscale patterning of binary self-assembled monolayers on nano-cylindrical substrates”, preprint.4. C Singh and SC Glotzer, “Ternary Janus and patchy particles”, preprint.5. AM Jackson, JW Myerson, F Stellacci, “Spontaneous assembly of subnanometre-ordered domains in the ligand shell of monolayer-protected nanoparticles”, Nature Materials, 3, 330-336 (2004).6. RP Carney, GA DeVries, C Dubois, H Kim, JY Kim, C Singh, PK Ghorai, JB Tracy, RL Stiles, RW Murray, SC Glotzer and F Stellacci, "Size limitations for the formation of ordered striped nanoparticles", Journal of American Chemical Society, (Communication), 130(3), 798-799 (2008).
5:30 PM - CC5.8
Controlled Clusters of Magnetic Nanoparticles by Dynamic Emulsion and Phase Separation Methods under Magnetic Field.
Tatsushi Isojima 1 , Su Kyung Suh 1 , John B. Vander Sande 1 , T. Alan Hatton 1 Show Abstract
1 Department of Chemical Engneering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
The functionality, assembly, and fabrication of functional nanoparticles, such as magnetic materials, noble metals, and quantum dots, are of increasing interest for a wide range of application areas and there is currently a strong scientific focus on the fundamental properties of such particles. Magnetite (Fe3O4) nanoparticles are especially useful in a wide range of fields. In many cases it is not the individual nanoparticles that are useful, since they generally do not respond strongly to magnetic fields, and it is desirable to form small clusters of these nanoparticles that are more responsive to moderate magnetic fields.We synthesized monodisperse nanomaginetic particle carted with oleic acid and oleil amine by Sun’s method (JACS 2002, 2004) for fabricated clusters. Controlled clusters of magnetic nanoparticles have been created by Solvent evaporation method from S/O/W type emulsion. These 100s nanometers clusters were categorized by spherical crystal clusters, amorphous clusters, toroidal clusters, coated polymer beads and Janus clusters. These clusters responded to applied magnetic fields to form structured chains.In our second approach, polymer-free magnetic fibers of magnetic nanoparticles have been created by Liquid-Liquid phase separation method under external magnetic field.The phase diagram consists of two different coexistence regions, one due to the simple binary mixture of the solvents, in which the nanoparticle dispersion is stable one of the two phases, and the other due to particle-particle interactions. The phase separating domains concentrated magnetic nanoparticles by particle-particle interactions were elongated into extremely long string structures in relatively weak external magnetic field (30mT), and stiffen these structures by quenching temperature into the inside coexistence curve or adding methanol at high temperature.
Erik Luijten University of Illinois, Urbana-Champaign
Sharon C. Glotzer University of Michigan-Ann Arbor
Francesco Sciortino Universitá di Roma “La Sapienza”
CC6: Fabrication and Assembly II
Thursday AM, December 04, 2008
Fairfax A (Sheraton)
9:30 AM - CC6.1
Simultaneous Synthesis and Assembly of Left-Handed Gold Nanoparticle Double Helices.
Chun-Long Chen 1 , Peijun Zhang 2 , Nathaniel Rosi 1 Show Abstract
1 Department of Chemistry, 219 Parkman Ave., University of Pittsburgh, Pittsburgh, Pennsylvania, United States, 2 Department of Structural Biology, 3501 5th Ave., University of Pittsburgh, Pittsburgh, Pennsylvania, United States
Thursday, 12/4New Presentation TimeCC6.1 @ 8:30 am - 8:45 amSimultaneous Synthesis and Assembly of Left-Handed Gold Nanoparticle Double Helices. Chung-Long Chen
9:45 AM - CC6.2
Dissipative Particle Dynamics Studies on the Self-Assembling Dynamics of the Peptide Amphiphiles.
Taiga Seki 1 , Noriyoshi Arai 1 , Taku Ozawa 2 , Tomoko Shimada 3 , Kenji Yasuoka 1 , Atsushi Hotta 1 Show Abstract
1 Graduate School of Science and Technology, Keio University, Yokohama Japan, 2 , JRI Solutions, Ltd., Tokyo Japan, 3 , Asahi Kasei Co., Tokyo Japan
Thursday, 12/4New Presentation TimeCC6.2 @ 8:45 AMDissipative Particle Dynamics Studies on the Self-Assembling Dynamics of the Peptide Amphiphiles.Taiga Seki
10:00 AM - CC6.3
Patchy Polymersomes with Tunable Morphologies.
Caterina LoPresti 1 , Giuseppe Battaglia 1 Show Abstract
1 , University of Sheffield, Sheffield United Kingdom
Thursday, 12/4New Presentation TimeCC6.3 @ 9:00 AMPatchy Polymersomes with Tunable Morphologies. Caterina LoPresti
10:15 AM - CC6.4
Nanomotors Based on Asymmetric Colloidal Particles and Rods.
Nicole Zacharia 1 , Leonardo Valadares 1 , Tihana Mirkovic 1 , Vladimir Kitaev 2 , Geoffrey Ozin 1 Show Abstract
1 Chemistry, University of Toronto, Toronto, Ontario, Canada, 2 Chemistry, Wilfred Laurier University, Waterloo, Ontario, Canada
Thursday, 12/4New Presentation TimeCC6.4 @ 9:15 AMNanomotors Based on Asymmetric Colloidal Particles and Rods. Nicole Zacharia
10:30 AM - CC6.5
Janus Gold Nanorods for Self-Limiting Lateral Assembly of Protostructures.
Robert MacCuspie 1 2 , Kyoungweon Park 1 2 , Michael Jespersen 1 2 , Andrea Elsen 1 3 , Jinsong Duan 1 , Ruth Pachter 1 , Richard Vaia 1 Show Abstract
1 Materials and Manufacturing Directorate, Air Force Research Lab, Wright-Patterson AFB, Ohio, United States, 2 , National Research Council, Washington, District of Columbia, United States, 3 Chemistry, Wright State University, Beavercreek, Ohio, United States
Thursday, 12/4New Presentation TimeCC6.5 @ 9:30 AMJanus Gold Nanorods for Self-Limiting Lateral Assembly of Protostructures. Robert I MacCuspie
10:45 AM - CC6.6
Fabrication of Polymeric Particles with Regular Surface Patches via Solution Assembly Kinetics.
Sheng Zhong 1 2 , Honggang Cui 1 2 , Jiahua Zhu 1 2 , Darrin Pochan 1 2 Show Abstract
1 Materials Science and Engineering, University of Delaware, Newark, Delaware, United States, 2 Delaware Biotechnology Institute, University of Delaware, Newark, Delaware, United States
Thursday, 12/4New Presentation TimeCC6.6 @ 9:45 AMFabrication of Polymeric Particles with Regular Surface Patches via Solution Assembly Kinetics. Sheng Zhong
11:30 AM - CC6.7
Assembly of Striped and Janus Monolayer Protected Gold Nanoparticles.
Hyewon Kim 1 , Francesco Stellacci 1 Show Abstract
1 Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
When monolayer protected gold nanoparticles are coated a self assembled monolayer composed of two types of immiscible thiolated molecules, spontaneous phase separation occurs in the ligand shell. In the case of particles in the ~ 2.5 nm to ~ 8.0 nm, quasi-ordered ribbon-like domains of alternating composition form. We call these striated domains ‘ripples’. We have shown that rippled particles are characterized by the presence of two polar point defects that can be selectively functionalized with target molecules. Effectively these ‘patchy’ particles behave as divalent nanoscale objects. In this talk, we will illustrate the assembly properties of these objects. In the case of particles of very small (< 2 nm) sizes, phase separation leads to the formation of Janus nanoparticles. Here we will show all the assembly properties that this class of ‘patchy’ particles has.
11:45 AM - CC6.8
Self-Assembly of Polyhedral Hybrid Colloidal Particles.
Adeline Perro 1 , Etienne Duguet 2 , Serge Ravaine 3 , Vinothan Manoharan 1 Show Abstract
1 School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States, 2 , Institut de Chimie de la Matière Condensée de Bordeaux - ICMCB, Pessac France, 3 , Centre de Recherche Paul Pascal - CRPP, Pessac France
We have developed a new method to produce hybrid particles with polyhedral shapes in very high yield (liter quantities at up to 75% purity) using a combination of emulsion polymerization and inorganic surface chemistry. The procedure has been generalized to create complex geometries, including hybrid line segments, triangles, tetrahedra, octahedra etc... The optical properties of these particles are tailored for studying their dynamics and self-assembly. For example, we produce systems that consist of index-matched spheres allowing us to define the position of each elementary particle in three-dimensions. We present some preliminary studies on the self-assembly of these complex shaped systems based on various optical experiments, including confocal microscopy, light scattering and electronic microscopy.
12:00 PM - CC6.9
The Effects of Shape Anisotropy on the Phase Behavior and Mechanical Properties of Polymer Colloids.
Ryan Kramb 1 , Charles Zukoski 1 Show Abstract
1 Chemical and Biomolecular Engineering, University of Illinois at Urbana Champaign , Urbana, Illinois, United States
Colloidal particles used in both experimental studies and theoretical predictions are most often spherical in shape. Because this shape is often easiest to synthesize as well as simplifies calculations, the vast majority of research in the field has been with spheres. Recently, an increasing number of studies have expanded synthesis techniques and theoretical models to include non-spherical shapes.The effect of shape anisotropy on the phase behavior and mechanical properties of colloidal systems has been predicted with the use naïve mode coupling theory (NMCT) calculations by Yatsenko and Schweizer.1 These calculations were performed assuming homonuclear, diatomic particle shape with a variable length to width (i.e. aspect) ratio. The results predict a nonmonotonic relationship between aspect ratio and glass transition volume fraction and as well as with elastic modulus. Calculations show a glass transition increasing from φ~0.43 for spherical particles (aspect ratio = 1.0), reaching a maximum of ~0.48 for an aspect ratio of ~1.4, and finally decreasing to below 0.4 for aspect ratios above 2.0. A corresponding trend can be seen for the dimensionless elastic modulus, G’D3/kT. At a fixed volume fraction, a minimum in the elastic modulus is predicted for an aspect ratio of ~1.4 with the largest moduli found at the extremes of 1.0 and >2.0. Experimental confirmation of these predictions has yet to be attempted. The goal of this work then has been to develop an experimental system to test the accuracy of the model. To accomplish this, ~850 nm polystyrene seed particles were synthesized with between 0 – 2.75 % divinyl benzene crosslinker. These particles were then swelled with additional styrene monomer and a second reaction was performed. This produced a “bump” on the crosslinked particles of varying size or simply increased the size of the noncrosslinked, linear particles. The resulting particles have aspect ratios of 1.0, 1.1 and 1.2 with an approximate average diameter of 1.2μm. The ionic strength and volume fraction of samples of these particles was systematically varied to determine the glass transition, gel point, and gel phase elastic modulus in each of these sets of particles. This experimental system will allow us to verify that shape anisotropy affects the properties of a colloidal system and determine if NMCT calculations predict the correct trends.(1) Yatsenko, G.; Schweizer, K. S., J. Chem. Phys. 2007, 126.
12:15 PM - CC6.10
Sculpting One-dimensional Nanocrystals of Chalcogenides: Sacrificial Templating and Surfactant-directed Core-shell Branching.
G. Ramanath 1 Show Abstract
1 Materials Science and Engineering (111 MRC), Rensselaer Polytechnic Institute, Troy, New York, United States
12:30 PM - CC6.11
Fabrication of Actuating Flexible Magnetic Filaments Through Co Nanoparticle Self-assembly.
Jason Benkoski 1 , Ryan Deacon 1 , Jennifer Breidenich 1 , Lance Baird 1 , Rengaswamy Srinivasan 1 Show Abstract
1 MERC, JHU Applied Physics Laboratory, Laurel, Maryland, United States
By self-assembling polymer functionalized cobalt nanoparticles, we demonstrate the formation of flexible magnetic filaments that measure approximately 1-5 um in length and only 25 nm in diameter. The nanoparticles measure approximately 25 nm in diameter and are coated with a benzaldehyde-functionalized polystyrene that can react with a diamine crosslinker in order to covalently link adjacent particles. Unlike rigid magnetic rods, which can only rotate or translate under the influence of an applied field, these segmented magnetic filaments can also bend in response to an external magnetic field. This degree of freedom can be exploited for unique micromechanical applications, as the bending filament is a common motif in biological systems. Flagella and cilia are perhaps the most common examples. In our study, we examine the effects of particle concentration, crosslinker concentration, reaction time, and external magnetic field strength on the size and morphology of the self-assembled filaments. We find that strong magnetic fields (~150 mT) induce phase separation that generates long, thick filaments. Weaker fields (<50 mT) yield filaments that measure only one particle wide (~25 nm). Lower particle concentrations result in fewer, thinner filaments. Taken together, the lack of influence from either reaction time or crosslinker concentration appear to indicate that the self-assembly of the nanoparticles occurs over much shorter time scales than the chemical crosslinking.
12:45 PM - CC6.12
General Templating Approaches towards Multi-Podal Nanoparticles with Functional Tethers.
Fan Li 1 , Won Cheol Yoo 1 , Molly Beernink 1 , Andreas Stein 1 Show Abstract
1 Chemistry Department, University of Minnesota, Minneapolis, Minnesota, United States
Self-assembly processes could benefit substantially from building blocks with anisotropic structures and functions. Nanoparticles (NPs) of anisotropic shape are building blocks of choice for many complex structures. Functional anisotropy (patching) is considered to facilitate the assembly process by establishing directional interactions. In this study we explore a general colloidal templating approach to create multi-podal nanoparticles with functional tethers on podal ends. The multi-podal structures were synthesized based on a reversed, ‘top-down’ strategy. For tetrapods, potential building blocks for diamond-like structures, the synthesis involved first molding a 3D ordered macroporous (3DOM) silica of centimeter size by replicating the interstitial space in a colloidal crystal template. The 3DOM replicas were then fractured into nanometer-level fragments of tetrapodal and truncated-octahedral shapes, defined by the colloidal crystal geometry. These particles could be selectively functionalized to achieve foot tethering. With a thiol-containing silane as grafting reagent, the selectivity of tethering was confirmed by attachment of Au NPs. Other functional groups could be grafted in the same manner, and the number of tethered feet could also be adjusted. We further extended this work to prepare tethered tripod particles by templating a close-packed colloid film. 1D nanorods with functionalized ends were also templated within a columnar porous membrane which was created by reactive ion etching with colloidal spheres. Overall, in this work, we demonstrated a complete spectrum of tethered multi-podal NPs, vividly mimicking the classic atomic valence structures of main group elements. The facile hard-templating approach should be applicable to a variety of compositions, and the study of the self-assembly of the tethered multi-podal structures is under way.