Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session C03: Self-assembly of Nanomaterials: Hierarchical assembly of nanoparticlesFocus
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Sponsoring Units: DCP Chair: Michael Gruenwald, University of Utah Room: LACC 150C |
Monday, March 5, 2018 2:30PM - 3:06PM |
C03.00001: Self-Assembly of Nanocrystal Superlattices: puzzles and opportunities Invited Speaker: Dmitri Talapin Nanoparticles of different functional materials can self-assemble from colloidal solutions into long-range ordered periodic structures (superlattices). Such assemblies provide a powerful platform for designing macroscopic solids with tailored electronic, magnetic, optical and catalytic properties. Unlike atomic and molecular crystals where atoms, lattice geometry, and interatomic distances are fixed entities, the arrays of nanocrystals represent solids made of “designer atoms” with potential for continuous tuning their physical and chemical properties. |
Monday, March 5, 2018 3:06PM - 3:18PM |
C03.00002: Structuring Matter over Multiple Length Scales using Hierarchical Self-Assembly Marjolein Dijkstra
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Monday, March 5, 2018 3:18PM - 3:30PM |
C03.00003: Ligand Interactions Determine Orientational Order in Self-Assembled Nanocrystal Superlattices Zhaochuan Fan, Michael Grunwald The self-assembly of colloidal nanocrystals into ordered structures is a straightforward and scalable method of creating functional nanomaterials. Predicting and controlling the structure that form during self-assembly, however, requires detailed knowledge of the interactions between nanocrystals in solution. Recent work has revealed that small semiconductor nanocrystals with polyhedral shapes can be assembled into a range of different superlattices that do not only differ by their lattice symmetry but also by the degree of orientational alignment between nanocrystals. Here, we show with coarse-grained modeling and molecular simulations that interactions between organic ligands on nanoparticle surfaces are crucial in determining these self-assembly outcomes. Our simulations reproduce well the experimental results obtained with 5-nm PbS nanocrystals and show that modest changes in solvent quality and surface density of ligands can lead to superlattices with different lattice symmetry and degree of orientational order. |
Monday, March 5, 2018 3:30PM - 3:42PM |
C03.00004: Self-Assembly of Chiral Nanoparticles Nicholas Kotov The field of chiral inorganic nanostructures emerged from the observation of strong circular dichroism for individual nanoparticles (NPs) and their assemblies. It includes now sophisticated nano-constructs from metals, semiconductors, ceramics, and nanocarbons with multiple chiral geometries with characteristic scales from Ångströms to microns. Uniquely high values of chiral anisotropy are attributed to resonances of incident electromagnetic radiation with plasmonic and excitonic states typical for metals and semiconductors. |
Monday, March 5, 2018 3:42PM - 3:54PM |
C03.00005: Coupling between long-range colloidal forces and short-range molecular details for better understanding of nanocrystal assembly Jaehun Chun, Christopher Mundy, Gregory Schenter Nanocrystal assemblies such oriented attachment (OA) unavoidably involve chemical physics at different length scales. As a result, the coupling between colloidal forces and molecular details would become critical to gain physical insights on nanocrystal assemblies. We used simple schemes to correlate the discrete nature of solvent (i.e., molecular details) to electrostatic and dispersion forces (i.e., colloidal forces) based on the spatial density response of a solvent at solid-liquid interfaces. Colloidal forces are shown to be sensitive to the spatial variation of solvent density, demonstrating appreciable deviations in the interactions from the conventional approach such as Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. Such “molecular granularity” concept can be also used to provide important insights on understanding of forces between mineral surfaces obtained from atomic force microscopy (AFM)-based dynamic force spectroscopy (DFS) |
Monday, March 5, 2018 3:54PM - 4:30PM |
C03.00006: Growth of Nanoscale Materials: Insights from Multiscale Theory and Simulations Invited Speaker: Kristen Fichthorn Metal nanocrystals have applications ranging from selective catalysts to electronic devices to localized surface-plasmon resonance-related applications. The versatility of functional nanocrystals relies on their tunable size and shape. To this end, solution-phase synthetic protocols have been highly successful at producing a variety of nanocrystal structures. However, great challenges remain in achieving high selectivity. A significant difficulty lies in understanding and controlling shape evolution. |
Monday, March 5, 2018 4:30PM - 4:42PM |
C03.00007: The Entropic Bond in Nanoparticle and Colloidal Assemblies Eric Harper, Greg Van Anders, Sharon Glotzer Chemical approaches to the study of matter are based on the notion of bonding. Chemical bonds rely on the reconfiguration of electronic structure to bind atoms and molecules. However, many of the characteristics of bonds such as hydrogen bonds, including directionality, cooperativity, and even thermal scale, could be satisfied by “bonds” that are neither quantum mechanical nor electromagnetic in origin. We demonstrate using a simple model of hard nanoplatelets that bonding mediated solely by entropy is analogous to bonding mediated by electron density. We quantify entropic bonding in terms of local entropy density and compute bond lifetimes, finding strong similarities between the behavior of entropic and hydrogen bonds. We demonstrate how to manipulate the structure of bonded states, thereby controlling entropic valence. We find that detailed knowledge of bonding in purely entropic systems can be used to deduce structural information about systems in which assembly is driven by enthalpic interactions arising from traditional chemical bonds. By realizing minimal requirements for bonding in mesoscale systems, our results open up the possibility of classes of systems in which bond properties can be continuously manipulated and designed. |
Monday, March 5, 2018 4:42PM - 4:54PM |
C03.00008: Optimization of Smooth Isotropic Pair Potentials for the Self Assembly of Complex Structures Carl Simon Adorf, James Antonaglia, Julia Dshemuchadse, Sharon Glotzer The synthesis of complex materials through the self-assembly of particles at the nanoscale provides opportunities for the realization of novel material properties. However, the inverse design process to create these materials is uniquely challenging. Standard methods for the optimization of isotropic pair potentials tend toward overfitting, resulting in solutions with too many features and length scales that are challenging to map to mechanistic models. Here we demonstrate how to effectively regularize the optimization of pair potential functions toward smooth and simple solutions by selectively amplifying relevant frequencies within the Fourier spectrum. Such simpler functions not only should be more readily realized experimentally, but also can be shown to be critical for robust self-assembly processes. |
Monday, March 5, 2018 4:54PM - 5:06PM |
C03.00009: Shape Transitions in Soft-Matter-Based Charged Nanoparticles Regulated by Surface Tension Nicholas Brunk, Vikram Jadhao Shape-reconfigurable nanoparticles (NPs) have important applications as self-assembling building blocks for the design of novel materials and as drug-delivery carriers that change shape in response to external cues. Experiments and simulations show that tunable short-range and long-range interactions can be used to deform soft-matter-based (soft) NPs. The shape and size of soft NPs is a function of surface composition and environment. In this work, molecular dynamics is used to explore the role of surface tension in deforming the shape of uniformly charged, soft NPs subject to a volume constraint. Results show that surface tension modulates the relative favorability of oblate disk to prolate rod morphologies. Disk-to-rod transitions are facilitated by increasing surface tension (1 - 20 dynes/cm). NPs with different bending rigidities (10 - 30 kBT), radii (10 - 30 nm), and surface charge (100 - 900 e) under variable solution ionic strengths (1 mM - 0.5 M) are investigated. Global free-energy changes and energy patterns on the NP surface are evaluated and correlated with the shape transitions. New pathways for the design of dynamic NP-based building blocks for hierarchical self-assembly are proposed. |
Monday, March 5, 2018 5:06PM - 5:18PM |
C03.00010: Guiding Self-Assembly of Functionalized Nanoparticles by Computational Modeling of Effective Interactions Vijay Shah, Alan Denton, Samuel Brown, Erik Hobbie Nanoparticles have attracted much attention due to their unusual optical and electronic properties, which vary in scale from molecular to bulk. Practical applications include optoelectronic materials and photovoltaic cells, which exploit self-assembly into crystalline arrays (superlattices). Bulk dispersions can be sterically stabilized against aggregation by functionalizing the particles with ligand brushes. Experiments have shown that silver nanoparticles coated with adsorbed oleylamine ligands can self-assemble into equilibrium superlattices in the presence of free ligands. However, the interplay between repulsive steric and attractive depletion interactions is not well understood. To better understand the role of adsorbed and free ligands in self-assembly, we perform molecular dynamics simulations to microscopically model silver nanocrystals coated with ligand chains immersed in a solution of free ligands. We extract the effective pair potential and input it into simulations of a coarse-grained model of nanoparticle dispersions to explore structure and phase stability. Our results offer potential insight into the design of experiments and fabrication of nanocrystal superlattices from other materials of practical interest, such as silicon. |
Monday, March 5, 2018 5:18PM - 5:30PM |
C03.00011: Formation and Structural Characterization of Large Area Thin Films of Elemental Pt Prepared at the Interface of Two Immiscible Fluids Jie Ren, Robert Schmidt, Gerald Poirier, Klaus Theopold, Karl Unruh Single and multilayered films of 5-6 nm diameter Pt nanoparticles self-assembled into 30-40 nm diameter aggregates have been prepared at the planar interface between an aqueous Pt colloidal solution and an immiscible fluid such as hexane. In order to achieve dense and essentially defect free films the zeta potential of the colloidal Pt must be adjusted to about -30 mV; more negative zeta potentials result in less uniform films while less negative zeta potentials lead to the precipitation of the nanoparticles. Interfacial Pt films with areas in excess of 40 cm2 can be easily transferred to a glass substrate for further study by evaporating and/or draining the two immiscible fluids. X-ray diffraction measurements on newly prepared single layer films reveal a significantly contracted Pt lattice parameter due to a surface stress induced Laplace pressure which slowly relaxes over time as the Pt surface oxidizes. |
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