Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session G30: Self-Assembly |
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Sponsoring Units: DCMP Chair: Bulent Akgun, National Institute of Standards and Technology Room: 338 |
Tuesday, March 19, 2013 11:15AM - 11:27AM |
G30.00001: Is a hierarchical dynamics the best route to the self-assembly of a hierarchical structure? Thomas Haxton, Stephen Whitelam Mimicking nature's ability to assemble functional hierarchical materials will require understanding how to promote the self-assembly of structure on multiple lengthscales while avoiding kinetic traps. We use computer simulation to study the self-assembly of a simple hierarchical structure, a square lattice whose repeat unit is a tetramer. Although the target material is organized hierarchically, it self-assembles most reliably when its assembly pathway consists of the sequential addition of monomers to a single structure. Hierarchical assembly pathways via dimer and tetramer intermediates result in lower yield, because these intermediates tend to associate in ways incompatible with the target structure. In addition, assembly via tetramers results in the formation of incomplete building blocks (trimers) that cannot combine to form the target crystal. We use analytic theory to relate assembly pathways to the underlying thermodynamics, identifying two principles for optimal assembly: 1) make the free energy gap between the target phase and the most stable fluid phase comparable to the thermal energy, and 2) ensure that no other dense phases (liquids or close-packed solids of monomers or oligomers) or fluids of incomplete building blocks fall within this gap. [Preview Abstract] |
Tuesday, March 19, 2013 11:27AM - 11:39AM |
G30.00002: Optimized assembly and steady-state length-scale control in dissipative systems of photo-switchable colloids Antonio Osorio-Vivanco, Monica Olvera de la Cruz, Sharon Glotzer Photo-switchable nanoparticles, such as those developed by Wei et al.,\footnote{Y.H. Wei, S. B. Han, J. Kim, S. L. Soh and B. A. Grzybowski, J. Am. Chem. Soc., 2010, 132, 11018-11020.} can be assembled into a broad range of structures using light exposure as a control parameter. Jha et al.\footnote{P.k. Jha, V. Kuzovkov, B.A. Grzybowski, and M. Olvera del la Cruz, Soft Matter, 2012, 8, 227-234} explored the evolution of these structures using kinetic Monte Carlo simulations. In this work, we build on these studies using Molecular Dynamics with a Langevin thermostat to, by judicious choice of exposure parameters that control the dissipative nature of the system, engineer and optimize the self-assembly pathways as well as control the length scales of the steady-state structures. [Preview Abstract] |
Tuesday, March 19, 2013 11:39AM - 11:51AM |
G30.00003: Self organization of exotic oil-in-oil phases driven by tunable electrohydrodynamics Anand Yethiraj, Atul Varshney, Shankar Ghosh, S. Bhattacharya The tuning of electrostatic interactions has helped to elucidate when coherent crystalline structures or incoherent amorphous structures form in colloidal systems. However, there is little understanding of self-organization in situations where hydrodynamic interactions are also present. We present a minimal two-component oil-in-oil model system where we can control the strength and length scale of the electrohydrodynamic interactions by tuning the amplitude and frequency of the imposed electric field. As a function of the hydrodynamic length scale, we observe a rich phenomenology of exotic structure and dynamics, from incoherent cloud-like structures and chaotic droplet dynamics, to polyhedral droplet phases, to coherent droplet arrays.\\[4pt] Reference: A. Varshney et al., Scientific Reports 2, 738 (2012). [Preview Abstract] |
Tuesday, March 19, 2013 11:51AM - 12:03PM |
G30.00004: Novel Behavior in Self-Assembled Superparamagnetic Nanoparticle Monolayers at the Air-Water Interface Jacob Stanley, Leandra Boucheron, Yeling Dai, Binhua Lin, Mati Meron, Oleg Shpyrko Iron oxide nanoparticles, coated with an oleic acid ligand, have been found to form self-assembled monolayers when deposited at the air-water interface. Even for low particle densities these particles aggregate into hexagonally close-packed islands which merge into a uniform layer at higher densities. Using Grazing Incidence Small Angle X-Ray Scattering (GISAXS) we were able to measure the first through fifth order diffraction peaks. By analyzing the positions and shapes of these peaks we investigated the in-plane structure of these monolayers and characterized how the structure changes as a function of compression in a Langmuir-Blodgett trough. Since iron oxide nanoparticles are known to be super-paramagnetic, we sought to investigate the role magnetic effects may have on the interparticle interactions and ordering within the film. We performed Grazing Incidence Diffraction (GID) measurements on the film while varying an external magnetic field. We will discuss the results of our findings. [Preview Abstract] |
Tuesday, March 19, 2013 12:03PM - 12:15PM |
G30.00005: Structure and dynamics of self-assembly Henrik van Lengerich, Richard James We investigate structures that are composed of many identical building blocks. Of particular interest are equilibrium structures where every building block sees the same environment - we call these ``objective structures''. For example, carbon nanotubes and virus capsids are both objective structures. The dynamics of assembly is investigated through experiments and simulations. The experiment consist of a macro-scale shaker containing identical neutrally buoyant magnetic particles. Simulations model the translation and rotation of particles using Langevin dynamics. This kind of modelling is applicable to both our experiment and to molecular assembly. [Preview Abstract] |
Tuesday, March 19, 2013 12:15PM - 12:27PM |
G30.00006: How to Maximize Self-Assembly in Free Surface Films by Resonant Wavelength Excitations Sandra Troian, Nan Liu Application of an external force probe on self-assembly processes in thin liquid films can offer significant insight into the fundamental dynamics of pattern formation. Less appreciated is the fact that modulation of such forces can induce resonant excitation effects in linearly unstable systems. While temporal modulation is rather common, there has been less emphasis on spatial forcing as a method for corralling emergent structure formation; such studies have also been strictly limited to 2D. In this talk, we call attention to a novel 3D hydrodynamic instability in nanoscale films whose free surface is exposed to a large uniform thermal gradient. Such films spontaneously develop arrays of nanopillars whose uniformity is often compromised by nanoscale inhomogeneities in film thickness, temperature and surface defects. In this talk we focus on resonant wavelength excitations induced by spatial modulation of the external thermal field near the linear stability point. Linear stability, weakly nonlinear analysis and simulations of the full nonlinear interface equation demonstrate the existence of a spatial coherence regime leading to more rapid growth and denser packing of perfectly uniform arrays, of significance to recent advances in lithographic patterning. [Preview Abstract] |
Tuesday, March 19, 2013 12:27PM - 12:39PM |
G30.00007: Analysis of pattern formation in systems with competing range interactions Vyacheslav R. Misko, Haijun Zhao, Francois M. Peeters Pattern formation is governed by competing interaction. Examples include: Langmuir monolayers, colloids and gels, ferrofluids, magnetic garnet thin films, type-I superconductors, the pasta phase in neutron stars, etc. We analyzed pattern formation and identified various morphologies in a system of particles interacting through a non-monotonic potential with a competing range interaction characterized by a repulsive core ($r < r_{c}$) and an attractive tail ($r > r_{c}$), using molecular-dynamics simulations [1]. Depending on parameters, the interaction potential models the inter-particle interaction in various physical systems ranging from atoms, molecules and colloids to vortices in superconductors. We constructed a ``morphology diagram'' in the plane ``critical radius $r_{c}$ $-$ density $n$'' and proposed a new approach to characterize the patterns. Namely, we elaborated a set of quantitative criteria in order to identify the different pattern types, using the radial distribution function (RDF), the local density function and the occupation factor. We also discuss the dynamics of the obtained patterns [2]. \\[4pt] [1] H. J. Zhao, V. R. Misko, and F. M. Peeters, New Journal of Physics {\bf 14}, 063032 (2012). \\[0pt] [2] H. J. Zhao, V. R. Misko, and F. M. Peeters, submitted (2012). [Preview Abstract] |
Tuesday, March 19, 2013 12:39PM - 12:51PM |
G30.00008: Crystallographic Tailoring: Self-Assembling Complex Crystals Through Building Block Design Pablo F. Damasceno, Michael Engel, Sharon C. Glotzer A primary challenge for the development of bulk, scalable and high yield materials with interesting properties is the limited number of structures that can be obtained via self-assembly of nano and micrometer sized particles. To increase this variability, several suggestions have been proposed among which the exploration of new anisotropic building blocks have received much attention. Here we present the results of a systematic and extensive computational study of hard polyhedral particles [1,2] and their subsequent assembly into a diverse range of complex structures. Our results show that 1) by utilizing more complex, anisotropically designed building blocks new structures can be self-organized purely from entropy maximization principles and, 2) a predictive criteria for assembly can be formulated, allowing for specific choices of building blocks given a target structure to be self-assemble. [1] Pablo F. Damasceno, Michael Engel {\&} Sharon C. Glotzer. ACS NANO (2012). [2] Pablo F. Damasceno, Michael Engel {\&} Sharon C. Glotzer. SCIENCE (2012). [Preview Abstract] |
Tuesday, March 19, 2013 12:51PM - 1:03PM |
G30.00009: Design Rules for the Self-Assembly of Voronoi Particles Benjamin Schultz, Pablo Damasceno, Michael Engel, Sharon Glotzer Recent theoretical advances have developed methodologies for predicting the assembly of hard, polyhedral particles. In this work, we use the Voronoi tessellation to generate polyhedral shapes that form space-filling superlattices that are isostructural to well-known atomic crystals. We focus on the assembly of these polyhedra into crystalline superlattices with orientational and positional order. Analogous to potentials designed to stabilize crystals at zero temperature, these particles are designed to stabilize the space-filling tiling at infinite pressure. We study a set of these particles in simulation and characterize how their symmetry and other geometric features affect their assembly characteristics at finite pressure. We calculate the relative stability of competing structures for several shapes that do not assemble their target structure and discuss how features of the shape affect this stability. From our conclusions, we demonstrate how to move beyond the concept of Voronoi tessellation for the design of hard polyhedral particles targeted for self-assembly. [Preview Abstract] |
Tuesday, March 19, 2013 1:03PM - 1:15PM |
G30.00010: Self-assembly of binary space-tessellating compounds Mihir Khadilkar, Umang Agarwal, Fernando Escobedo Self-assembly of polyhedral nanoparticles and their mixtures has been a topic of interest in both experimental and simulation studies due to its potential to help engineer novel materials. Hard-core mixtures that tessellate space are particularly interesting since they are expected to form entropy-driven high-pressure ordered structures. Using Monte Carlo simulations, we study three such binary tessellating mixtures; namely, cuboctahedra + octahedra (Mixture 1), octahedra + tetrahedra (Mixture 2), and truncated cubes + octahedra (Mixture 3). We see that upon gradual compression of the isotropic system, Mixtures 1 and 2 form a metastable, glassy disordered phase while Mixture 3 demixes into a disordered phase and an unusual `semi-crystalline' phase where truncated cubes form a cubic lattice while the octahedra remain disordered occupying interstitial pockets. While our results identify some relations between properties of individual species and their mixtures, they also illustrate the potential of tessellating mixtures as designable materials that can lead to novel equilibrium phases or serve as entropic glass formers. Preliminary results on non-tessellating binary mixtures will also be briefly discussed to provide a broader context of the results for the tessellating cases. [Preview Abstract] |
Tuesday, March 19, 2013 1:15PM - 1:27PM |
G30.00011: Targeted self-assembly of complex lattices and meta materials from isotropic interactions Oskar Lindgren, Erik Edlund, Martin Nilsson Jacobi I will present an analytical method for designing isotropic interactions causing particles to self-assemble into complex lattices. The method is direct as opposed to previous trial and error schemes where the interactions are modified and tested until the desired pattern self-assembles. Since a naive implementation of the design scheme generally yields interaction potentials too complicated to implement experimentally, we provide a systematical simplification scheme to minimize the interaction potentials' complexity without changing which pattern is produced by the self-assembly process. We also prove that our suggested simplification scheme is optimal. The method has been tested using simulated systems and proven to work for a wide range of patterns, ranging from chiral 2D surfaces to 3D diamond-like crystals. The recent improvements in simplicity for the designed potentials makes experimental realization feasible. The interactions can also be designed so that the self-organizing systems obtain different material properties like directional sound propagation or stealth-like properties via the diffraction pattern. [Preview Abstract] |
Tuesday, March 19, 2013 1:27PM - 1:39PM |
G30.00012: Rheology of Self-Assembling Colloidal Chains Kazem V. Edmond, Stefano Sacanna, Zachary D. Forbes, Andrew D. Hollingsworth, David J. Pine We probe the rheology of self-assembling chains of ``pacman'' particles using a Zimm viscometer, a modified Couette apparatus. Pacman particles are microscopic spherical particles specially designed to have a spherical indentation on their surface. In the presence of a depletant, overlap between the indentation and another particle's surface maximizes the excluded volume between the two interacting particles, resulting in a selective attraction between them. Careful tuning of the interaction strength in a suspension of particles induces the formation of long chains. Shearing this material can twist, stretch, and break the chains, causing the material to exhibit unique rheological properties. [Preview Abstract] |
Tuesday, March 19, 2013 1:39PM - 1:51PM |
G30.00013: Shaping Colloids for Self-Assembly Stefano Sacanna, Gi-Ra Yi, David Pine The creation of a new material often starts from the design of its constituent building blocks at a smaller scale. From macromolecules to colloidal architectures, to granular systems, the interactions between basic units of matter can dictate the macroscopic behavior of the resulting engineered material and even regulate its genesis. Information can be imparted to the building units by altering their physical and chemical properties. In particular, the shape of building blocks plays a fundamental role at the colloidal scale, as it can govern the self-organization of particles into hierarchical structures and ultimately into the desired material. Herein we report a simple and general approach to generate an entire zoo of new anisotropic colloids. Our method is based on a controlled deformation of multiphase colloidal particles that can be selectively liquified, polymerized, dissolved and functionalized in bulk. We further demonstrate control over the particle functionalization and coating by realizing patchy and Janus colloids. [Preview Abstract] |
Tuesday, March 19, 2013 1:51PM - 2:03PM |
G30.00014: Probing transition pathways of self-assembled colloidal clusters Rebecca W. Perry, Miranda Holmes-Cerfon, Michael P. Brenner, Vinothan N. Manoharan Clusters of colloidal particles bound by weak interactions explore rich energy landscapes characterized by a few minima and many higher-energy, non-rigid configurations. To investigate how such systems transit through their energy landscapes, we designed a two-dimensional system that lends itself to simple observations with brightfield video microscopy. In our aqueous system, a short-range depletion interaction strongly confines the diffusion of the spherical polystyrene colloids to a shallow volume close to a glass cover slip. The same depletion interaction provides reversible bonds between the spheres. Analyzing time series of clusters of 3, 4, and 6 spheres allows us to compare the free energy of rigid configurations to that of the transition states and to measure the kinetics of the transitions. Combining experimental measurements of the kinetics with a recent theory using a geometrical approach for calculating energy landscapes leads to a new understanding of how hydrodynamics effect transitions rates between energy minima. [Preview Abstract] |
Tuesday, March 19, 2013 2:03PM - 2:15PM |
G30.00015: Optical assembly of thermodynamically stable colloidal clusters mediated by depletion Bhaskar Jyoti Krishnatreya, Stefano Sacanna, Kazem Edmond, David Pine, David G. Grier Colloidal particles with complementary shapes can self-organize into composite structures under the influence of entropic attractions mediated by depletion. What structures can form is governed by the colloidal components' shapes. The structures' stability can be tuned by adjusting the strength of the depletion attraction. Even when a particular colloidal cluster configuration is thermodynamically stable, achieving the stable structure typically involves substantial kinetic barriers. We overcome these kinetic barriers by assembling geometrically organized colloidal clusters using holographic optical tweezers in three dimensions. Once formed, the structures are stable and undergo three-dimensional shape fluctuations that can be measured with video microscopy. [Preview Abstract] |
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