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2008 APS March Meeting New Orleans, Louisiana 2008 APS March Meeting New Orleans, Louisiana http://www.aps.org/meetings/march/index.cfm i Monday, March 10, 2008 8:00AM - 11:00AM — Session A8 DFD: Colloidal Self-Assembly I Morial Convention Center RO6 8:00AM A8.00001 Directed Self-Assembly of Spherical Particles NATALIE ARKUS, GUANGNAN MENG, VINOTHAN MANOHARAN, MICHAEL BRENNER, Harvard University — We examine the kinetics and energetics of self-assembly in systems containing a small number of spherical colloidal nanoparticles using a combination of theory, simulation, and experiment. We then explore how the addition of spherically symmetric binding specificity can be used to direct the self-assembly of a given structure. Using graph theoretic, numerical, and algebraic geometric techniques, we denumerate all possible packings for a system of n particles. We map out the energy landscape of these packings, which is determined not only by the value of the potential energy at these minima, but also by the vibrational normal modes of the structures. Experiments for a 6 particle system show that the likelihood of a given packing follows this expected equilibrium distribution. To explore the kinetics of packing formation, we simulate the self-assembly of these systems in the irreversible binding limit. For the 6 particle system, this reveals that the kinetics required to form one of the packings is highly unlikely, resulting in the other packing forming with 100% probability. With the addition of binding specificity however, we can cause the unlikely packing to form with 100% probability. We show how the addition of binding specificity effects the energetic landscape of these systems, and that it alone is sufficient to direct self-assembly. 8:12AM A8.00002 Controlling assembly of micro- and nano-particle systems with DNA. , DMYTRO NYKYPANCHUK, MATHEW MAYE, DANIEL VAN DER LELIE, OLEG GANG, Brookhaven National Laboratory — Addressable biological interactions provide attractive platform for rational self-assembly, however the strength of such interactions are often difficult to control. Here we present an approach where DNA molecules are used to balance attractive and repulsive interactions during particles assembly while preserving the interaction addressability. We show, that by changing the composition and structure of DNA shall of micro- (2 um) or nanoparticles (10 nm), assembly kinetics, aggregate sizes, and the systems melting properties can be tuned. At constant environmental conditions, this strategy allows for rational control of interaction energy landscape for nano- and micro-systems in a wide dynamic range. 8:24AM A8.00003 Evaporation-Driven Assembly of Microspheres with Polymer in Emulsion Droplets1 , KENG-HUI LIN, Institute of Physics, Academia Sinica, Taipei, Taiwan, LIANG-JIE LAI, Dept. of Physics, National Central University, Chung-li, Taiwan, CHIH-CHUNG CHANG, HUI CHEN, Dept. of Chemical and Materials Engineering, National Central University, Chung-li, Taiwan — We study the packing of colloidal microspheres mixed with polymer in oil-in-water emulsion droplets through evaporation. The addition of polymer produce non-unique configurations of final clusters when the number of particles N inside the droplet is larger than 4. The cluster configurations are classified into three categories based on the symmetry. Stablized colloidal clusters of spherical packings are observed. Observation on packing process shed light to the mechanisms which cause different and non-unique structures. The osmotic pressure and interparticle interaction due to polymer play important roles in packing. 1Support for this work is provided by NSC Grant No. 96-2112-M-001 8:36AM A8.00004 Entropy-driven self-assembly of dimers , ISSEI NAKAMURA, AN-CHANG SHI, McMaster University — Supramolecular self-assembly is an important phenomenon with applications ranging from chemical synthesis to biological systems. Although the driving force of assembly is the weak non-covalent intermolecular interaction such as hydrogen bonding and dispersion force, the self-assembly is a result from balancing the enthalpic and entropic contributions. In general, the disassembled/disordered phase is expected as temperature is raised because of the entropic gain from the components of the aggregate. However, it has been observed that the self-assembled/ordered phase can be promoted with increasing temperature. This implies that the self-assembly is driven by entropy. In order to provide a better understanding of this entropy-driven transition, we have studied a statistical mechanical model for the aggregation of macromolecular dimers immersed in solvents. The model demonstrates that solvent molecules absorbed on the surface of the solute are released with increasing temperature, leading to an increase of the total entropy of the system. Consequently, the cooperative stability of the dimeric state is induced. The thermodynamic features of this transition are analyzed. 8:48AM A8.00005 Hydrodynamic interactions effects on the dipole-induced self-assembly of β- peptides and Brownian-induced polymer pore translocation , JUAN HERNANDEZ-ORTIZ, Departamento de Materiales, Universidad Nacional de Colombia, Sede Medellin, MICHAEL GRAHAM, JUAN DE PABLO, Department of Chemical and Biological Engineering, University of Wisconsin-Madison — A novel method that scales linearly with the number of particles is used to study Brownian-systems considering fluctuating hydrodynamic interactions. The method is demostrated in the concept of two applications: the dipole-induced self-assembly of β-peptides and the Brownian-motion-induced translocation of a polymer thought a rectangular pore. The method includes the long-range interactions by the Green’s function formalism. It allows the consideration of peptides at intermediate concentrations and the inclusion of the non-periodic domain of the translocation. The hydrodynamics interactions affect the dynamics of the peptides agglomeration and the mean-squared-displacement indicates significant changes in the long-time diffusion coefficient. The polymer translocation is study using a transition path sampling based methodology. In particular it is used to calculate the translocation rate constant. Even for a single bead there are differences once hydrodynamics are included. These differences are due to the changes of mobility near walls and the change in polymer chain diffusion coefficient. 9:00AM A8.00006 Self-assembly of complex shaped colloidal particles , ADELINE PERRO, VINOTHAN N. MANOHARAN, Harvard School of Engineering and Applied Sciences — 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 optical properties of these particles are tailored for studying their dynamics and self-assembly. For example, we produce systems that consist of index-matched sphere doublets with a small strongly scattering inorganic core between the two spheres, allowing us to track the center of mass of each doublet. We have generalized the preparation procedure to create even more complex geometries, including hybrid tetrahedra and octahedra. We present some preliminary studies on the self-assembly of these systems based on various optical experiments, including confocal microscopy, light scattering, and digital holographic microscopy. 9:12AM A8.00007 Progress on systems of DNA modified colloidal particles for self-replication , PAUL CHAIKIN, MIRJAM LEUNISSEN, REMI DREYFUS, ROUJIE SHA, NADRIAN SEEMAN, DAVID GRIER, DAVID PINE, New York University — Our goal is to create new materials that can self-replicate and self-assemble. For this, we modify the interactions between micrometer-sized colloids by coating them with single-stranded DNA ‘sticky ends’, which specifically recognize complementary sequences on other colloids. We find that the aggregation-dissociation behavior is fully reversible for at least tens of temperature cycles. Using magnetic beads or optical tweezers, we form a chain-like ‘seed’ structure, which acts as a template to assemble copies of itself from a soup of singlets. To determine what are the preferred binding sites, we studied the interactions between the singlets and their complementary particles in the seed. Important in our replication scheme is that each particle has two different types of sticky ends: one for ‘longitudinal’ bonding along the chain and another for ‘transverse’ bonding between seed and daughter chains. Contrary to the transverse linkers, the longitudinal linkers form AT/TA bonds, which can be crosslinked with an intercalator and UV irradiation. In this way, we permanently fix the seed and its copies. 9:24AM A8.00008 Binary Colloidal Assembly by Dielectrophoresis , PETER HOFFMAN, YINGXI ELAINE ZHU, University of Notre Dame — Dielectrophoresis (DEP)-driven colloidal assembly has been recently explored as a new route to manipulate colloids and rapidly form nanostructured materials. In this talk, we demonstrate that colloidal particles of varied sizes can be assembled with controllable packing configurations in the presence of AC-electrical fields. We investigate binary latex particles of varied size ratios from 0.25 to 0.8 and directly monitor the dynamic assembly process with final structural characterization by using high-speed confocal microscopy. We observe rich phase behaviors of binary colloidal assembly with a strong dependence of applied AC-field frequency and medium conductivity. The obtained structural phase diagram can be well predicted
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