Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session B02: Self-assembly of Nanomaterials: Mechanisms of Structure FormationFocus
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Sponsoring Units: DCP Chair: James De Yoreo, Pacific Northwest National Laboratory Room: LACC 150B |
Monday, March 5, 2018 11:15AM - 11:51AM |
B02.00001: Building models for the initial stages of nucleation: CaCO3 revisited Invited Speaker: Christopher Mundy Building quantitative models of nucleation remains a challenge in both simulation and theory. |
Monday, March 5, 2018 11:51AM - 12:03PM |
B02.00002: Understanding crystallization pathways through in situ characterization and theory Maria Sushko, jinhui tao, Yingwen Cheng, James De Yoreo, Jun Liu The potential of a general synthetic approach for multiscale structural control by manipulating the interfacial nucleation and self-assembly of nanoscale building blocks is demonstrated using an integrated theoretical and experimental approach. The control over crystallization pathways across different length scales is demonstrated using two classes of nucleation and growth processes: crystallization on well-defined surfaces, and seeded growth of metal and metal oxide nanostructures. The developed theoretical framework for modeling interfacially directed crystallization pathways and a suite of in situ characterization techniques for monitoring nucleation and crystal growth processes were used to show that the interfacial solvent structure and ion distributions are critical controls for surface-directed nucleation. Using a model system of gold nanoparticles, we have shown that the correlated fluctuation dynamics of growth solutions in the interfacial region largely dictate nucleation and growth pathways in seeded growth processes. Applying these principles to more complex systems and utilizing interfacial surfactant templating and temperature-induced phase transformations in surfactant templates produced highly regular 3D porous materials. |
Monday, March 5, 2018 12:03PM - 12:15PM |
B02.00003: Revealing Mechanisms of Spontaneous Chiral Resolution with Molecular Models John Carpenter, Michael Grunwald The separation of racemates is an essential step in the development of many bioactive organic compounds. Current methods of separation, however, can be costly and inefficient. For a small subset of chiral compounds, separation of enantiomers happens conveniently through spontaneous enantiopure crystallization. Despite computational and experimental efforts to understand this phenomenon, little is known about its driving forces and mechanisms. |
Monday, March 5, 2018 12:15PM - 12:27PM |
B02.00004: Assembly and reformation of structured liquids at the water-oil interface Yu Chai, Alysia Lukito, Yufeng Jiang, Jaffar Hasnain, Phillip Geissler, Paul Ashby, Thomas Russell Nanoparticle-surfactant (NPS) assembled at water− oil interfaces can significantly lower the interfacial tension and reversibly transition from a solid like jammed state to a liquid state enabling the stabilization of non-equilibrium shaped domains of liquids. Understanding the formation and assembly and actively tuning the packing of these NPSs are of fundamental interest for the interfacial behavior of nanoparticles and of interest for water purification, drug encapsulation, enhanced oil recovery, and innovative energy transduction applications. We demonstrate the high ionic strength helps the adsorption of NPSs to the water− oil interface leading to a denser packing of NPSs at the interface by means of the interfacial tension measurement. With the reduction of interfacial area, the phase transitions from a “gas” -like to “liquid” to “solid” states of NPSs in two-dimension are proposed and observed. We show the first in situ real-space imaging of NPSs at the water− oil interface by atomic force microcopy, how different sized NPs compete and affect the pattern of the assembled films, and the generation of nano-patterned fluidics with optical and scanned probe based lithography. |
Monday, March 5, 2018 12:27PM - 1:03PM |
B02.00005: Nanoparticle driven nucleation of inorganic and macromolecular crystals Invited Speaker: Alexander van Driessche Crystallization from solution, a omnipresent process in both natural and industrial environments, can follow a variety of pathways, including nanoparticle driven nucleation which includes the formation, aggregation and transformation of these particle during the early stages of crystal formation. This multistep mechanism has been observed for both organic (e.g. a model protein) and inorganic (e.g. sulfate salts) crystalline materials [e.g. 1-3]. Detailed, in situ studies of these systems have allowed us to establish a comprehensive picture of the crystallization dynamics and based on those findings we are now able to understand polymorph selection [4] and elucidate novel strategies to control crystallization. In this talk, an overview of nanoparticle driven nucleation will be presented for an inorganic and a macromolecule system. Special emphasize will be placed on the role of the primary nanoparticles in the outcome of the crystallization process, and how this can be used to control the nucleation pathway by adding for example organic polymers. |
Monday, March 5, 2018 1:03PM - 1:15PM |
B02.00006: Barrier-free Nucleation of 2D Phage-selected Peptide Films on MoS2 Surfaces Jiajun Chen, Enbo Zhu, Juan Liu, Yu Huang, Hendrik Heinz, James De Yoreo Assembly of 2D patterns on crystal surfaces has been widely investigated to reveal the structural and energetic relationships between substrate and overlying architecture. Progress has been achieved in understanding and controlling their assembly, yet little is known about the mechanism by which they nucleate. Understanding the dominant pathways and formation kinetics would enable precise control over phase and morphology during synthesis of 2D materials. In our study, short peptides were selected for their ability to bind on MoS2 (0001). We studied nucleation and growth of 2D films of these peptides with in situ AFM and compared our results to MD simulations. We find the peptide arrays exhibit an epitaxial relationship to the underlying lattice, but assemble row-by-row from dimeric growth. The nuclei are ordered from the earliest stages. Although the final crystals are 2D, due to the 1D nature of the constituent rows, there is no critical size and the nucleation rate varies linearly with concentration and is finite for all concentrations above the solubility limit. Our results verify long-standing but unproven predictions of CNT while revealing the key interactions responsible for ordered assembly. |
Monday, March 5, 2018 1:15PM - 1:27PM |
B02.00007: Design Principles for Non-equilibrium Self-Assembly Suriyanarayanan Vaikuntanathan Understanding the principles governing self-assembly re- mains an important problem in statistical mechanics. We find, surprisingly, that general design principles for this challenging problem can be obtained by applying ideas from the field of stochastic thermodynamics to nonequilibrium self-assembly problems. Our central results constrain the set of possible configurations achievable under a nonequilibrium drive. |
Monday, March 5, 2018 1:27PM - 1:39PM |
B02.00008: Spatially Localized Quasicrystals Priya Subramanian, Andrew Archer, Edgar Knobloch, Alastair Rucklidge We investigate quasicrystal-forming soft matter such as dendrimers and star block copolymers, using a two-scale phase field crystal model. At state points near thermodynamic coexistence between bulk quasicrystals and the liquid phase, we find multiple metastable spatially localized quasicrystals embedded in a background of liquid. We use the terminology of spatially localized quasicrystals to refer to structures that turn into an extended quasicrystal in a continuous manner when a system parameter is varied. In two dimensions, we compute several families of spatially localized quasicrystals with dodecagonal structure and investigate their properties as a function of the system parameters. In three dimensions we obtain spatially localized icosahedral quasicrystals. In both 2D and 3D the localized quasicrystals are metastable, and so correspond to energetically locally favored structures. The presence of such structures is expected to crucially affect the dynamics of the crystallization process. |
Monday, March 5, 2018 1:39PM - 1:51PM |
B02.00009: Nucleation and structural growth of cluster crystals Christian Leitold, Christoph Dellago We study the nucleation of crystalline cluster phases in the generalized exponential model with exponent n=4. Due to the finite value of this pair potential for zero separation, at high densities the system forms cluster crystals with multiply occupied lattice sites. Here, we investigate the microscopic mechanisms that lead to the formation of cluster crystals from a supercooled liquid in the low-temperature region of the phase diagram. Using molecular dynamics and umbrella sampling, we calculate the free energy as a function of the size of the largest crystalline nucleus in the system, and compare our results with predictions from classical nucleation theory. Employing bond-order parameters based on a Voronoi tessellation to distinguish different crystal structures, we analyze the average composition of crystalline nuclei. We find that even for conditions where a multiply-occupied fcc crystal is the thermodynamically stable phase, the nucleation into bcc cluster crystals is strongly preferred. Furthermore, we study the particle mobility in the supercooled liquid and in the cluster crystal. In the cluster crystal, the motion of individual particles is captured by a simple reaction-diffusion model introduced previously to model the kinetics of hydrogen bonds. |
Monday, March 5, 2018 1:51PM - 2:03PM |
B02.00010: Crystallographically Preferred Growth in Self-assembled Colloidal Crystals: A Mechanistic Study Ling Li, Haizhao Yang, Katherine Phillips, Jinjin Zhong, Jianfeng Lu, Joanna Aizenberg Crystalline atomic and ionic solids are often textured due to preferred growth along specific crystallographic orientations. In this talk we demonstrate that crystallographically-preferred growth can also be observed in colloidal crystals through an evaporation-induced self-assembly process. By using quantitative crystallographic mapping, we find that the preferred <110> growth in the fcc lattice of the colloidal crystal is achieved through a gradual crystallographic rotation, facilitated by geometrically necessary dislocations (GNDs). Complementary microscopic investigation at the single-particle level indicates that, similar to crystalline metals, individual dislocations disassociate to two Shockley partial dislocations, creating a hcp stacking fault in the fcc lattice. We show that the origin of these dislocations is drying-induced tensile stress in the meniscus direction in the colloidal crystal and that the associated experimentally observed primary slip systems are consistent with the classical atomistic theory, giving rise to GNDs of the same slip system that rotate individual grains to the <110> direction to minimize stress. |
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