Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session V07: Programmable Self-Assembly: Particle, Interaction and Pathway Design (Shape/Entropic Interactions)Live
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Sponsoring Units: DSOFT Chair: Douglas Hall, University of Massachusetts Amherst; Itai Cohen, Cornell University Room: 07 |
Thursday, March 18, 2021 3:00PM - 3:12PM Live |
V07.00001: Pushing the Limits of Size Control for Geometrically Frustrated Assembly of Ribbons and Rings Douglas Hall, Mark J Stevens, Gregory M Grason Robust control of equilibrium assembly sizes allows templating, scaffolding and functional materials at scales much larger than the dimensions of the building blocks. Geometrically frustrated assembly achieves this size control, where assembly stress can accumulate over lengths determined by both the geometry of molecular misfit and assembly elasticity. The limits of this size control depend on modes of assembly softness. |
Thursday, March 18, 2021 3:12PM - 3:24PM Live |
V07.00002: Geometrically Frustrated Self-assembly of Curved Colloidal Particles Nabila Tanjeem, Douglas Hall, Christian Santangelo, Gregory M Grason, Ryan Hayward Geometrically frustrated systems where local order fails to propagate globally can lead to self-assembly that limits the size of equilibrium structures. We study an example of such geometrically frustrated self-assembly in which plate-like particles with a preferred curvature stack due to an attractive face-to-face interaction. Achieving perfect contact between the curved particles (‘curvamers’) forces them to bend, resulting in an elastic energy cost. The equilibrium size of the self-assembled stacks is finite and determined by the ratio of the bending energy to the adhesive energy. We developed a model of the curvamers and performed molecular dynamics simulations to realize the self-limiting behavior. The model allows us to investigate the geometry of the self-assembled stack and understand the role of the attractive potential between curvamers. In the case of long-ranged potentials, we observe the opening of gaps between curvamers that allows them to ‘escape’ frustration, while in the case of short-ranged potentials, we observe break-up into smaller stacks consistent with self-limiting assembly. Our model, combined with future experiments, helps to elucidate the role of geometric frustration in determining the size and geometry of self-assembled structures. |
Thursday, March 18, 2021 3:24PM - 3:36PM Live |
V07.00003: Bioinspired self-healing polypeptides Abdon Pena-Francesch, Melik Demirel, Metin Sitti Recent research efforts have focused on developing soft, flexible, compliant materials for robotics, biointerfacing, and biosensing applications. Because of their intrinsic softness, these materials are susceptible to cut, puncture, scratch, and/or tear damage that compromise their physical integrity, and therefore self-healing properties are indispensable for soft machines and devices operating in dynamic environments. Here, we introduce self-assembled polypeptides that self-heal micro- and macro-scale mechanical damage within a second via reversible physical cross-linking. These proteins are systematically optimized to improve their hydrogen-bonded nanostructure and network morphology, with healing properties (~25 MPa strength after 1 second of healing) surpassing those found in other natural and synthetic soft materials by several orders of magnitude. Such healing performance opens new opportunities for bioinspired materials design, and addresses current limitations in self-healing materials for soft robotics and wearable technology. |
Thursday, March 18, 2021 3:36PM - 3:48PM Live |
V07.00004: Entropically engineered fivefold and icosahedral twin clusters of colloidal shapes Sangmin Lee, Sharon C Glotzer Multiply twinned structures with fivefold or icosahedral symmetry have been extensively studied to control the growth and final shape of synthetic nanomaterials with those symmetries. Numerous methods have been proposed to control the formation of such structures, and complicated interparticle interactions or geometric confinement are widely considered to be essential. Here, we report the purely entropy-driven formation of fivefold and icosahedral twin clusters in hard particle Monte Carlo simulations. Hard truncated tetrahedra self-assemble into either cubic or hexagonal diamond crystals depending on the amount of edge and vertex truncation. By engineering particle shape to achieve a negligible free-energy difference between the cubic and hexagonal diamond phases, we show the formation of fivefold or icosahedral twin clusters in colloidal fluids through seed-assisted growth. The icosahedral twin cluster of hard truncated tetrahedra can be entropically stabilized within a dense fluid due to strong fluid-crystal interfacial tension, unlike hard spheres where interfacial tension is weak. Our findings show that twinning behavior and fluid-crystal interfacial properties in hard particle systems can be entropically engineered to obtain fivefold and icosahedral twin clusters. |
Thursday, March 18, 2021 3:48PM - 4:00PM Live |
V07.00005: Congruent Phase Behavior of a Binary Compound Crystal of Colloidal Spheres and Dimpled Cubes Isabela Quintela Matos, Fernando A Escobedo We performed Monte Carlo simulations to study the phase behavior of equimolar mixtures of spheres and cubes having selective inter-species affinity. Such selectivity was designed to promote the formation of the substitutionally ordered NaCl compound, the C* phase, and to be driven by energetic bonds and also by entropic bonds generated by dimples on the cube facets. The spheres' nestling in the cube indentations can promote negative nonadditive mixing and increase the C* phase packing entropy. The focus is on congruent phase behavior wherein the C* phase directly melts into the disordered state. We used a thermodynamic integration scheme to trace the coexisting curves for varying values of the interspecies contact energy, ε*, the relative indentation size, λ, and the sphere-to-cube size ratio, ζ. By starting from a known coexistence point, we find that increasing λ (at fixed ε* and ζ) reduces the free-energy and pressure of the C* phase at coexistence. Remarkably, a purely athermal C* phase formed for λ>0.7 and specific ζs. We suggest a metric of a nonadditive volume of mixing as an approximate predictor of athermal C* phase stability. We expect the principles developed in this study to apply to other particle shapes and crystalline phases. |
Thursday, March 18, 2021 4:00PM - 4:12PM Live |
V07.00006: Local signatures of emerging global order in complex crystal growth Maya Martirossyan, Matthew Spellings, Julia Dshemuchadse Designing and building functional materials requires an understanding of how different crystal structures grow—depending on their complexity, local motifs, and symmetry. Currently, the manner in which particle-particle interactions lead to the emergent formation of any given crystal structure remains a mystery. Using molecular dynamics simulations of particles interacting via isotropic pair potentials, we assemble a diverse set of complex crystal structures [1] and observe the crystallization process. With a machine-learning-powered order parameter [2], we classify particles by their local environments into different phases and crystalline positions. We examine the progression of crystal growth on a local level to illuminate the emergence of long-range order from short-range interactions. |
Thursday, March 18, 2021 4:12PM - 4:24PM Live |
V07.00007: Self-Assembly of Chiral Metal-Organic Cages at the Presence of Chiral Counterions: Chirality Effects on the Intermolecular Interactions Ehsan Raee, Hui Li, Xinyu Sun, Putu Ustriyana, JIANCHENG LUO, Jiahui Chen, Nita Sahai, Tianbo Liu One of the most important questions about the chirality of biological molecules is their effect on the intermolecular interactions specially during supramolecular formation leading to homochiral structures. In this work, positively charged alanine-based D- and L-Pd12Ala24 metal organic cages (MOCs) self-assemble into single-layered hollow spherical blackberry-type supramolecular structures by adding extra nitrates through counterion-mediated attraction. Moreover, it was observed that enantiomers of small chiral counterions, although possessing similar chemical and physical properties, have a hugely different effect on the inter-cage electrostatic interaction. While D-counterion does not show any significant effect on the interaction between D-Pd12Ala24 MOCs and consequently on their self-assembly behavior, L-counterions notably reduce the self-assembly rate, size of the blackberry structures, and concentration of the assemblies by having a higher binding strength to the MOCs and inhibiting the nitrate counterions, which trigger the self-assembly process, to bind to the cages. The same story can be observed for L-Pd12Ala24 and D-counterions. This work provides evidence on homochirality phenomena observed in biological supramolecules. |
Thursday, March 18, 2021 4:24PM - 4:36PM Live |
V07.00008: Anisotropic Nanocrystal Shape and Ligand Design for Co-Assembly Katherine Elbert, William E Zygmunt, Thi Vo, Corbin Vara, Daniel Rosen, Nadia Krook, Sharon C Glotzer, Christopher B Murray In recent years, there has been increasing emphasis on using anisotropic building blocks to create metamaterials with emergent properties. However, unlike single shaped particle or co-assembly of binary spheres, there have been few reports of co-assembly of two anisotropic NCs that do not rely on explicit usage of shape complementarity. Here, we present a theory-driven approach for designing the co-assembly of cubes and triangular prisms. Specifically, we employ theory to select for a combination of design parameters that exhibit a broad co-assembly regime. Key to this process is the idea of removing geometrical incompatibilities between building blocks via tuning the shape of the ligand shell coating individual NCs. Direct applications of our design parameters are then shown to produce the predicted co-assembly behavior in experiments. This work sheds light on the cooperative role of both shape and ligand shell in directing the organization of multi-shaped objects. |
Thursday, March 18, 2021 4:36PM - 4:48PM Live |
V07.00009: Frustrated Self-Assembly of Non-Euclidean Crystals of Nanoparticles Francesco Serafin, Jun Lu, Nicholas Kotov, Kai Sun, Xiaoming Mao Many complex structures in nature such as living organisms self-organize from simple units. They display high complexity, which allows multiple functions, and at the same time are efficient, adaptable and robust. |
Thursday, March 18, 2021 4:48PM - 5:00PM Live |
V07.00010: Aggregation Transitions in a Minimal Model of Geometrically Frustrated Assembly Nicholas Hackney, Gregory M Grason Geometric frustration has been recognized as an important framework for understanding a wide range of self-assembling systems where the balance between the cohesive gains of assembly and the cost of frustration can result in unique, scale-dependent thermodynamics. One salient behavior is the existence of equilibrium states characterized by finite-sized aggregates that are much larger in size than the individual sub-units they are made of. The continuum models used to describe these assemblies derive their thermodynamics from the ground-state elastic energetics - ignoring finite temperature effects. We describe a 2D lattice model of geometrically frustrated assembly, which encodes both positional and “shape misfit” degrees of freedom of assembling subunits. We exploit this model to examine the relationship between aggregation temperature, concentration and frustration. In the continuum limit, we find that - for fixed sub-unit concentration - increasing frustration depresses the critical aggregation temperature, while also reducing the mean aggregate dimensions. These predictions are explored via Monte Carlo simulation. This work serves as a first step towards a more detailed understanding of the thermodynamics of geometrically frustrated assembly. |
Thursday, March 18, 2021 5:00PM - 5:12PM Live |
V07.00011: Size control and escape mechanisms in geometrically frustrated assemblies Botond Tyukodi, Farzaneh Mohajerani, Gregory M Grason, Michael F Hagan The self-limited assembly (SLA) of building blocks into structures with large, but well-defined finite sizes, is an essential capability of biological systems. Developing human-engineered building blocks with a similar ability to undergo SLA is of great interest in nanotechnology. Recently, it has been theoretically proposed that SLA can be achieved through ‘geometric frustration’, in which the preferred local packing of subunits is incompatible with their preferred large-scale assembly structure. |
Thursday, March 18, 2021 5:12PM - 5:24PM Live |
V07.00012: Learning to grow: control of material self-assembly using evolutionary reinforcement learning Stephen Whitelam, Isaac Tamblyn We show that neural networks trained by evolutionary reinforcement learning can enact efficient molecular self-assembly protocols. Presented with molecular simulation trajectories, networks learn to change temperature and chemical potential in order to promote the assembly of desired structures or choose between competing polymorphs. In the first case, networks reproduce in a qualitative sense the results of previously-known protocols, but faster and with higher fidelity; in the second case they identify strategies previously unknown, from which we can extract physical insight. Networks that take as input the elapsed time of the simulation or microscopic information from the system are both effective, the latter more so. The evolutionary scheme we have used is simple to implement and can be applied to a broad range of examples of experimental self-assembly, whether or not one can monitor the experiment as it proceeds. Our results have been achieved with no human input beyond the specification of which order parameter to promote, pointing the way to the design of synthesis protocols by artificial intelligence. |
Thursday, March 18, 2021 5:24PM - 5:36PM Live |
V07.00013: Bioinspired Self-Assembly of Hollow Nanoparticles Saranshu Singla, Zepeng Yang, Anvay Patil, K Zin Htut, Matthew Shawkey, Ali N Dhinojwala Structural colors, produced by interaction of light with nanostructures, have garnered significant interest among researchers because of their potential to replace toxic pigments and developing inks that do not fade upon exposure to light. The non-iridescent structural colors in birds are produced by combinations of keratin, melanin and air. This strategy has inspired some intriguing mimics for producing structural colors using self-assembly of polydopamine (PDA) nanoparticles, a synthetic analogue of melanin. Even though melanin is necessary for producing saturated colors, excess melanin content can lead to loss in brightness. In my presentation, I will discuss our strategy to create core-shell and hollow nanoparticles of various shell thicknesses using polystyrene (PS) nanoparticle template and coating it with PDA, providing a very high refractive index contrast. The PS core than can be dissolved away to produce saturated colors. We will present the reflectance data and our optical simulation results to explain the changes in colors between the core-shell and hollow nanoparticles. Understanding the physics of color generation would benefit a wide variety of applications including paints, coatings, and cosmetics. |
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