Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session L31: DSOFT Early Career Award and Directed Assembly IPrize/Award
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Sponsoring Units: DSOFT Room: 503 |
Wednesday, March 4, 2020 8:00AM - 8:36AM |
L31.00001: Early Career Award for Soft Matter Research talk Invited Speaker: Stefano Sacanna Colloidal self-assembly today is increasingly focused on the development of particles that mimic atomic properties. Atoms serve as inspiration for what simple but ideal building blocks are capable of, and through the mastery of relatively few design principles, such as directionality, valence, and well-defined bonds, many target architectures become rationally accessible. A colloidal diamond lattice, for example, theoretically operates as an exotic semiconductor for light, and is just now becoming available through molecular mimetic routes. Myriad syntheses have been developed to accomplish this by targeting specific geometries and surface patterns, which serve to direct assembly. In this talk, I will break down and categorize the wide selection of colloidal reactions available by using an analogy to synthetic chemistry, helping to index and navigate the ever-expanding colloidal toolbox. Beginning with elementary colloidal particles, I will define the set of directions synthetic routes can take, firstly, through inter-particle reactions, which combine disparate particles into new well-defined units and secondly through intra-particle reactions, which occur through a particle’s internal transformation. I will also discuss the most prominent colloidal interactions available for assembly, and which are most useful for a given synthetic route. Today, long-sought-after target structures are just coming to fruition, so it is an ideal time in the colloidal community to examine the most efficient ways to generate particles and how to make them assemble. Drawing from many fields including colloid and surface chemistry, supramolecular chemistry, biochemistry, and photonics, molecular mimetic colloids represent a point of interest for any materials scientist. |
Wednesday, March 4, 2020 8:36AM - 8:48AM |
L31.00002: Colloidal Diamond Crystals Mingxin He, Johnathon Gales, Etienne Ducrot, Zhe Gong, Gi-Ra Yi, Stefano Sacanna, David J Pine Self-assembling colloidal diamond has been a longstanding goal because of the structure's potential for photonic applications. Because particles in a diamond lattice are tetrahedrally coordinated, one approach has been to self-assemble spherical particles with tetrahedral sticky patches. Difficulties persist, however, because the patchy particles possess no mechanism to select the proper staggered orientation of tetrahedral bonds on nearest-neighbor particles, a necessary requirement for cubic diamond. Here, we show that by using partially compressed clusters with retracted sticky patches, colloidal cubic diamond can be self-assembled using patch-patch adhesion together with a steric interlock mechanism that selects the proper staggered bond orientation. Colloidal particles in the self-assembled diamond structure are highly constrained and mechanically stable, which makes it possible to dry the suspension and retain the diamond structure. The inverse lattice exhibits promising photonic properties, including a complete photonic bandgap. |
Wednesday, March 4, 2020 8:48AM - 9:00AM |
L31.00003: Colloidal Diamond Photonic Bands Johnathon Gales, Mingxin He, David J Pine We have designed a new set of patchy tetrahedral colloidal clusters that can self-assemble into a diamond lattice. Like the conventional colloidal diamond of spheres, we find that the diamond lattice of clusters we have assembled exhibits a strong photonic band gap for appropriate parameters. Inverting the lattice leads to a particularly strong band gap after optimizing a few geometric parameters. We also provide a method for achieving the inverse lattice. |
Wednesday, March 4, 2020 9:00AM - 9:12AM |
L31.00004: Photonic band gaps in self-assembled colloidal structures Duanduan Wan, Sharon C Glotzer An intriguing feature of colloids is their ability of self-assembly, i.e., colloidal particles arrange themselves into an ordered structure. Using computer simulations, we explore the effect of thermal disorder on the photonic band gap in a self-assembled photonic crystal. We find that photonic band gaps can exist over a large range of intermediate packing fractions and that the widest gap does not necessarily appear at the densest packing fraction. Further, we show that with judicious choices of particle shape, packing fraction, and particle internal structure, self-assembly can be a promising method to make photonic crystals with large band gaps despite the presence of disorder. |
Wednesday, March 4, 2020 9:12AM - 9:24AM |
L31.00005: Rational Design of Patchy Colloids Capable of Self-Assembling into Open Crystal Lattices with Complete Photonic Bandgaps Yutao Ma, Andrew L Ferguson Patchy colloids equipped with anisotropic interactions are promising building blocks whose self-assembly provides a powerful tool for forming many complex functional materials. A main challenge in the self-assembly of patchy colloids is the design of colloidal geometry and chemistry that favor the formation of target structure thermodynamically and kinetically. We have previously developed a rational design protocol, called landscape engineering, in which we recover the free energy surface governing colloidal self-assembly process by combining molecular simulation with nonlinear dimensionality reduction technique and sculpt the free energy surface by modifying the colloidal design using genetic algorithm to make target structure thermodynamically favorable. We have applied this protocol to successfully design patchy colloids capable of self-assembling into pyrochlore lattice and cubic diamond lattice consisting of tetrahedral clusters via two-stage temperature control. Both structures are defect-free and possess complete photonic bandgaps. Our method may be extended to the rational design of self-assembling colloidal molecules and other systems such as peptides. |
Wednesday, March 4, 2020 9:24AM - 9:36AM |
L31.00006: Nanoparticle Superlattices with Polymer Ligands Alex Travesset, Nathan R Horst, Jianshe Xia, Hongxia Guo We provide a study of the assembly of single component nanocrystals (nanoparticles) NCs capped with polystyrene by solvent evaporation. We investigate regimes from the colloidal RG/RC<<1 with R_C (core radius) and RG (ligand gyration radius) to the polymer limit RG/RC>>1. We show that for increasing chain length, there is the emergence of a ``cascade effect'', i.e. an abrupt drop in internal energy with the resulting potential of mean force dominated by configurations wherein the chains bend over the core in order to maximize contacts with the other NC, which accounts for the large magnitude of the many body effects in the superlattice free energy. Interestingly, the Orbifold Topolgical Model (OTM) that successfully characterizes the nanocrystal interaction in the colloidal limit, quantitatively describes the polymer limit as well. Our results establish that bcc is the equilibrium phase. Implications for recent and future experiments are discussed. |
Wednesday, March 4, 2020 9:36AM - 9:48AM |
L31.00007: Binary colloidal compounds with depletants Ali Ehlen, Hector Manuel Lopez Rios, Monica Olvera De La Cruz We study the effects of depletants on binary size-asymmetric colloidal crystals. Specifically, we discuss the mechanism that leads to two types of systems: 1) stable compound crystals of large repulsive particles with smaller particles; and 2) crystals of large repulsive particles stabilized by a mobile sublattice of small particles. This talk will address the impact of the presence of depletants in both the compounds and in the sublattice-melted crystals, as well as the relative significance of the attractive interaction between the particles and the depletion forces. |
Wednesday, March 4, 2020 9:48AM - 10:00AM |
L31.00008: Phase Diagram and Structure Map of Binary Nanoparticle Superlattices from a Lennard-Jones Model Shang Ren, Yang Sun, Feng Zhang, Alex Travesset, Cai-Zhuang Wang, Kai-Ming Ho In this work, we show that a binary system interacting through Lennard-Jones (LJ) potential predicts all phases reported in experiments in which nanoparticles are effectively described as quasi hard spheres. Furthermore, we show that binary lattices may be described as combinations of a small number of particle clusters, motifs, which generalize the four Z-N that describe Frank Kasper phases. We report a phase diagram consisting of 53 equilibrium phases, whose stability is quite insensitive to the microscopic details of the potentials, thus giving raise to some universality. Our results show that meta-stable phases share the same motifs as equilibrium phases. Connections with packing models, phase diagrams with repulsive potentials and the prediction of new superlattices in experiments are thoroughly discussed. |
Wednesday, March 4, 2020 10:00AM - 10:12AM |
L31.00009: Novel mesophase behavior in two-dimensional binary solid solutions Prajwal Bangalore Prakash, Fernando A Escobedo Towards the goal of designing new complex materials, Monte Carlo simulations were used to study the entropic-driven assembly of binary mixtures of hard polygons and disks. Two distinct types of mixtures were studied, such that individual components either form distinct crystal lattices, like squares and disks, or similar crystal lattices, like hexagons and disks. Our focus was the 2D phase behavior of mixtures where the components have size ratios that optimize their co-assembly into solid solutions, and over the full range of compositions and concentrations to further detect any partially ordered phases (mesophases). Besides the enhanced regions with solid miscibility, a novel mosaic/polycrystalline phase was found for the disk+square mixtures and a rotator-plastic solid phase for the disk+hexagon mixtures. The mosaic phase has interspersed clusters of locally ordered 4-fold squares and 6-fold disks, distributed throughout the domain with random orientations. The plastic-solid rotator mesophase of hexagons and disks exhibits long-range translational and short-range orientational order. Changes in phase behavior for different component size ratios were also investigated to assess the importance of the optimal size ratio in promoting mesophase behavior. |
Wednesday, March 4, 2020 10:12AM - 10:24AM |
L31.00010: Diffusion of DNA-coated colloids on DNA coated surface Jeana(Aojie) Zheng, Sophie Marbach, Miranda Holmes-Cerfon, David J Pine DNA-coated colloids can self-assemble and crystalize into a wide variety of structures. In order for DNA-coated colloids to anneal and form crystals, they must roll and diffuse while attached to each other. Here we report on the diffusion of DNA-coated colloidal spheres on a flat DNA-coated substrate. Near the DNA-melting temperature, the mean square displacement is linear in time as expected for normal diffusion, but the diffusion coefficient is much smaller than for free diffusion. As the temperature is lowered, the motion becomes sub-diffusive, which suggests the presence of random free energy barriers in the DNA-mediated interactions. We have found that DNA induced interactions are highly sensitive to the density and homogeneity of the DNA distribution. As we reduce the DNA density, the DNA coated colloids diffuse slower. Here we also report the modeling of melting curve for particle - substrate binding, allowing to understand and predict how binding properties depend on parameters of the DNA-coated colloids (salt concentrations, DNA sequence, etc.) This study is important for designing and optimizing self-assembly structure of DNA coated colloids. |
Wednesday, March 4, 2020 10:24AM - 10:36AM |
L31.00011: 3D self-replication of DNA nanostructures Feng Zhou, Heng Ni, Ruojie Sha, Nadrian C Seeman, Paul M Chaikin Self-replication is a natural process that can generate materials and pass along information. We have seen several examples of artificial self-replication in which the template assembles, organizes and directs formation of the target nanostructure. However, the self-assembly procedure increases the template's dimensionality, which makes it challenging to template and replicate a 3D object. Here, we report the direct self-replication of a 3D object. First, we fabricate a three face cube corner as our template. The replication proceeds by self-assembling three daughter origami tiles to three edges of the cube corner. DNA single strands on each cube face and daughter tile hybridize to fold the tiles inward and complete the cubic box. The daughter tiles are then cross-linked into a new cube corner. Heating releases the two complementary cube corners. This method provides a general approach for conducting high-order self-replication by organizing the materials via folding. Considering that the 3D DNA nanostructure is a functional platform, this type of 3D self-replication can produce new materials, such as chiral plasmonic nanomaterials, by passing the steric information through successive generations. |
Wednesday, March 4, 2020 10:36AM - 10:48AM |
L31.00012: Self-assembled helical structures of ABCD star tetrablock copolymer within cylindrical confinement Paresh Chokshi, Supriya Gupta Physical confinement of block copolymers plays an important role in generating a rich variety of novel ordered phases not seen in bulk systems. These novel ordered microstructures, arising mainly out of structural frustration and confinement-induced entropy loss, provide ideal templates to self-assemble nanoparticles. In order to generate novel multicomponent helical structures, we investigate the four-armed ABCD star tetrablock copolymers for their equilibrium states under cylindrical nanopore confinement with the help of self-consistent field theory. The ABCD star tetrablock copolymer exhibits rich self-assembly behaviour with myriads of three-dimensional ordered phases ranging from one-component, two-components and three-components helices to honeycomb-like structures depending upon the individual block fractions and the size of cylindrical nanopore. Such chiral structural motifs generated from achiral polymeric molecules are fascinating due to superior performance in sophisticated optical functions. The comprehensive understanding of the self-assembly behaviour enables one to design novel nanostructured materials with desired material properties. |
Wednesday, March 4, 2020 10:48AM - 11:00AM |
L31.00013: Toward generating colloidal cubic phases: Shape sensitivity of the Ia(-3)d gyroid phase in hard pear-shaped particle systems Philipp Schönhöfer, Gerd Schroeder-Turk The ambition to mimic highly complex and functional nanostructures found in living organisms marks one of the pillars of today's research in bio- and soft matter physics. Here, self-assembly has evolved into a prominent strategy in nanostructure formation. However, it is still a challenge to design and realise particle properties such that they self-organise into the desired target configuration. One key design parameter is the (effective) shape of the constituent particles. |
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