Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session K54: Self and Directed Assembly I: Colloids |
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Sponsoring Units: GSOFT Chair: Thomas Mason, Dept. of Physics and Astronomy, University of California - Los Angeles Room: LACC 514 |
Wednesday, March 7, 2018 8:00AM - 8:12AM |
K54.00001: Self-assembled topological metamaterials: Weyl points for light and sound Michel Fruchart, Seung-Yeol Jeon, Kahyun Hur, Vadim Cheianov, Ulrich Wiesner, Vincenzo Vitelli Soft materials such as liquid crystals, block copolymers, or colloidal particles can self-assemble into highly structured phases which replicate at the mesoscopic scale the symmetry of atomic crystals. As such, they offer an unparalleled platform to design metamaterials for light and sound. Here, we present a bottom-up approach based on self-assembly to engineer three-dimensional photonic and phononic metamaterials with topologically protected Weyl points. In addition to angular and frequency selectivity of their bulk optical response, Weyl metamaterials are endowed with topological surface states, which allows for the existence of one-way channels even in the presence of time-reversal invariance. Using a combination of group-theoretical methods and numerical simulations, we identify the general symmetry constraints that a self-assembled structure has to satisfy to host Weyl points, and describe how to achieve such constraints using a symmetry-driven pipeline for metamaterial design and discovery. |
Wednesday, March 7, 2018 8:12AM - 8:24AM |
K54.00002: Phase behavior in polydisperse microgel suspensions controlled by spontaneous particle deswelling Urs Gasser, Andrea Scotti, Emily Herman, L. Andrew Lyon, Alberto Fernandez-Nieves Crystallization is often suppressed by point defects due to larger impurity particles. Surprisingly, microgels can overcome this limitation: Large microgels can spontaneously deswell to fit into the crystal lattice of smaller but otherwise identical microgels. We find this particle deswelling to be triggered by a difference in osmotic pressure, Π, between the inside and the outside of the particles. Π is set by the counterions of charged groups on the microgels. A Π-difference between inside and outside of a microgel builds up when the counterion clouds of neighboring particles overlap. This causes an increase of Π in the space between particles, which is not compensated inside the particles. With increasing concentration, this Π-difference exceeds the bulk modulus of the softest and largest microgels and makes them deswell, enabling crystallization. We find the freezing point of poly- and bidisperse suspensions to be linked to particle deswelling: A reduction of polydispersity due to deswelling is required for crystallization. Compared to monodisperse suspensions, this causes the freezing point to shift to higher concentrations. In comparison to incompressible colloids, this particle deswelling mechanism fundamentally changes the role of polydispersity in microgel suspensions. |
Wednesday, March 7, 2018 8:24AM - 8:36AM |
K54.00003: Structures and Assembly Pathways of Colloidal Clusters Ellen Klein, William Rogers, Solomon Barkley, Vinothan Manoharan We experimentally study colloidal clusters of 6 to 100 spherical particles bound together by short-range attractions. These clusters are a model system for understanding colloidal self-assembly and dynamics, since the positions and motion of all particles can be observed. For 10 particles and fewer, the ground states are degenerate, and, as shown in previous work [1], the probabilities of observing specific clusters depend primarily on their rotational entropy, which is determined by symmetry. Thus, less symmetric structures are more frequently observed. However, for larger clusters the ground states appear to be subsets of close-packed lattices, which tend to have higher symmetry. To understand how this transition occurs as a function of the number of particles, we assemble and then anneal an ensemble of clusters. We fit a generative model to confocal microscopy data and then characterize the number of apparent ground states, their symmetries, and their probabilities as a function of the number of particles. We also study how these structures form by forming a chain of colloidal particles and watching it fold into its minimal-energy configuration. |
Wednesday, March 7, 2018 8:36AM - 8:48AM |
K54.00004: Line-slip defects in colloidal crystals on a cylinder Nabila Tanjeem, Henry Wilkin, Daniel Beller, Christopher Rycroft, Vinothan Manoharan We study crystallization of colloidal spheres on the surface of a cylinder. Because a cylinder has zero Gaussian curvature and can accommodate a finite number of particles around its circumference, different crystalline structures assemble, depending on the ratio of the particle size to cylinder size. When a perfect crystal cannot be accommodated, the densest packing is achieved by having a line-slip defect, Such defects consist of a line of particles, each of which has one fewer contact than in bulk. We study these defects with an experimental system consisting of submicron-sized colloidal spheres that assemble into hexagonal lattices on a drawn silica fiber with a diameter of a few microns. The assembly is driven by a short-ranged depletion interaction. By varying the ratio of the sphere size to the fiber diameter, we find crystals with different chirality and line-slip structure. We find ground state line slips with one straight helical line, but also a new type of line slip with kinks. We see that some of the kinks disappear over time and reach the ground state of straight line slips. To explain this experimental observation, we perform finite temperature simulations on the system and find that the kinks represent low energy excitations of the system. |
Wednesday, March 7, 2018 8:48AM - 9:00AM |
K54.00005: Soft Potential for the Self-Assembly of Colloidal Clusters and Spheres, Structures and Photonic Band Gaps Etienne Ducrot, Johnathon Gales, Gi-Ra Yi, David Pine We recently demonstrated experimentally and in simulations that DNA coated tetrahedral clusters and spheres self-assemble into a colloidal analog of the MgCu2 structure[1], interpenetrated diamond and pyrochlore lattices. For very short range attractive potential between building blocks, the desired superstructure only forms when clusters are partially compressed. Under those conditions, merging particles in the cluster is necessary to fill the gap between the two sublattices, increase the number of contacts between complementary particles and stabilize the final assembly. |
Wednesday, March 7, 2018 9:00AM - 9:12AM |
K54.00006: DNA Patchy Particles via Fluid Solid Transition Jairo Diaz, David Pine DNA is an exceptional tool to direct self-assembly in colloids. Nevertheless, making complex or even functional arbitrary assemblies is still quite challenging. We present a novel route to create solid colloids with DNA patches holding different sequences that can expand the number of realizable self-assembled structures. Patch symmetries and DNA types are sorted in the liquid phase, while controlled transition to the solid phase freezes-in DNA designs for further assembly. High surface diffusion of DNA strands during fluid assembly enables us to obtain stable patchy particles with desired symmetries in the order minutes. The resultant high density of DNA strands within patches can drive the assembly over densely DNA coated particles. New multi-DNA patchy particles hold promise to access metastable regions in phase diagrams and unique opportunities for complex self-assembly. |
Wednesday, March 7, 2018 9:12AM - 9:24AM |
K54.00007: Dimer Crystallization of Proteomimetic Colloidal Chiral C-Shapes by Steric Pathway Selection in Slowly Crowded Enantiopure Monolayers Thomas Mason, Po-Yuan Wang Inspired by crystals of dimerized proteins, we lithographically create monodisperse proteomimetic colloidal particles, or "proteoids". We show that 2D Brownian systems of certain chiral C-shaped proteoids can self-assemble into dimer crystals when slowly crowded. Using depletion attractions, we form long-lived enantiopure Brownian monolayers of mobile, microscopic, polymeric proteoids that are dispersed in water and have nearly hard in-plane interactions. Adding a circular head to an achiral C-shape yields a chiral proteoid. This head sterically blocks one of two pathways for chiral dimerization, leading to enantiopure lock-and-key dimerization. Complementary corrugations in the chiral dimers that form also lead to ordering of these dimers into crystals. Using optical microscopy, we reveal that tautomerization translocation reactions (TTRs) enable monomer defects to be expelled from growing crystallites. We lithographically mutate the location of the circular head on the proteoid and show that even small changes can significantly affect the primitive vectors of the dimer crystals. Thus, remarkably, the equivalent of a quinary level of protein self-assembly can be achieved by simply crowding certain shape-designed hard proteoids in the presence of entropic Brownian fluctuations. |
Wednesday, March 7, 2018 9:24AM - 9:36AM |
K54.00008: Forming 2D colloidal crystals (sometimes) with sedimented colloids Yijun Dong, Peiyao Wu, James Kindt, Eric Weeks We use bright field microscopy to observe the phase behavior of the base layer in a gravitationally confined colloidal system of silica particles. After injecting the colloidal of particles into a chamber and giving the system sufficient amount of time for sedimentation, we observe those particles settling on the base of the chamber forming a static quasi-2D structure. We control two parameters of the system, namely the particle concentration and the Peclet number. The Peclet number measures the relative importance of the gravitational force over the thermal effects, and is positively related to the particle diameters. We find that the most ordered states are formed by heavy particles (with high Peclet numbers) at moderately high concentrations. Simulations on the gravitationally confined quasi-2D system are conducted simultaneously, aiming to understand the relation between the phase behavior and various factors, including the polydispersity and the initial state of the system. |
Wednesday, March 7, 2018 9:36AM - 9:48AM |
K54.00009: Exploring Nucleation Pathways and Solid-solid Transitions in Two-dimensional Colloidal Crystallization Huang Fang, William Rogers Crystallization, which is found in many natural and manmade systems, describes a phase transition between a disordered and an ordered state, or a pathway on a phase diagram. Although the final crystal structures that emerge are often well understood, the microscopic pathways, which could go through a number of metastable intermediates, are difficult to observe or predict. Do the particles form the final crystal structure directly? Do they form metastable structures first and then transform? And do the pathways they follow influence their final symmetry or order? In this talk, I will present a combination of computer simulations and video microscopy experiments investigating the crystallization pathways of DNA-coated colloids. We explore the role of the relative strengths of interactions in determining the pathway, symmetry, and compositional order in crystallization of a binary suspension. We observe a rich diversity of behavior, including both one- and two-step nucleation pathways, as well as solid-solid transitions between crystal phases. These results may help shed light on the fundamental nature of crystallization, as well as provide new methods for controlling the self-assembly of materials made from colloids. |
Wednesday, March 7, 2018 9:48AM - 10:00AM |
K54.00010: Linker-mediated binding of DNA-grafted colloids: New phase diagrams and how to predict them Janna Lowensohn, Guillermo Narvaez Paliza, Bernardo Oyarzún, Bortolo Matteo Mognetti, William Rogers DNA is a promising tool for programming the self-assembly of new materials: its interactions are chemically specific, tunable, and predictable. However existing approaches rely on direct hybridization of DNA strands grafted to colloidal particles and thus are too limited in their design space to create some of the more interesting structures, such as aperiodic materials or systems comprised of hundreds of unique particle species. In this work, we explore an alternative paradigm in which particles interact through DNA strands dissolved in solution instead of through direct binding of grafted strands. We find that the phase behavior that emerges in our linker-based system is surprisingly rich, exhibiting a re-entrant melting transition at high linker concentrations and a region of stable coexistence between solid and fluid. We reproduce our observations quantitatively using an equilibrium statistical mechanical model, which takes as inputs the linker concentration, grafting density, and DNA sequences. Going forward, we expect that these linker-based systems could present other interesting possibilities, like new kinds of interactions whose specificity depends on temperature. |
Wednesday, March 7, 2018 10:00AM - 10:12AM |
K54.00011: Paramagnetic Colloidal Chians in Rotating Fields: Chaotic Routes to Periodic Orbits Hamed Abdi, Rasam Soheilian, randall erb, Craig Maloney We present computer simulations and experiments on dilute suspensions of |
Wednesday, March 7, 2018 10:12AM - 10:24AM |
K54.00012: Selective DNA-Functionalization of Janus Particles and Their Self-assembly Joon Suk Oh, Gi-Ra Yi, David Pine Janus particles are quite unique building blocks due to their anisotropic nature. Unlike isotropic particles, it has been known that they can self-assemble into various structures such as micelles, vesicles, chains, bilayers, etc., due to their directional and geometrical interactions. One of the key factors governing the self-assembly behavior of Janus particles is the patch ratio, the ratio between the surface of the attractive patch and the total sphere surface. However, it is still challenging to control the patch ratio with existing methods. Here, we exhibit a novel fabrication method allowing us to accurately adjust the patch ratios of Janus particles in a wide range. Then, we show how to selectively functionalize one of the patches with DNA using a swelling-deswelling method for DNA-mediated self-assembly. Last, we demonstrate that the DNA-coated Janus particles can bind with each other only through the DNA-coated patches and self-assemble into various structures such as clusters, chains, rings, and bilayers. |
Wednesday, March 7, 2018 10:24AM - 10:36AM |
K54.00013: Polymer-Functionalized Nanocrystal Interactions During Superlattice Self-Assembly Nathan Horst, Alex Travesset Programmable self-assembly of nanoscale components into ordered structures provides the foundation for an emerging, exciting class of materials. Understanding interactions between the nano-ingredients of these systems is a primary goal of the computational and theoretical community as we strive to develop more precise models to characterize and predict real systems. Various techniques have been discovered to synthesize these materials, including the functionalization of nanocrystallites by DNA, hydrocarbons or polymers. These functional components drive the assembly of the system, but little is understood about explicit configurational changes of the functional groups during assembly. We present an investigation of these systems, with emphasis on examining polymer systems and the effect of solvent quality, from brush polymers to the star-polymer regime. Specifically, we evaluate the potential of mean force between a pair of nanocrystals, as well as elucidate configurational characteristics of the polymer functional groups during this interaction. |
Wednesday, March 7, 2018 10:36AM - 10:48AM |
K54.00014: Nanoparticle Superlattices as Quasi-Frank Kasper Phases Alex Travesset I show that all phases reported experimentally in binary nanoparticle superlattices can be de- |
Wednesday, March 7, 2018 10:48AM - 11:00AM |
K54.00015: Interface mediated assembly and evaporation driven deposition of Janus particles Shan Jiang, Kyle Miller, Emily Olson, Nancy Sweeney We study the self-assembly of Janus particles during the drying process inside a thin aqueous film. It has been discovered that Janus particles form unique drying patterns, which are distinctively different from those formed by homogeneous particles. By tracking both translational and rotational dynamics of Janus particles, different stages of drying process were revealed. The orientation of Janus particles are strongly influenced by the interface. The effects of drying condition, substrate and Janus balance will be discussed. |
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