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 B07: DSOFT 2020 Prize SessionFocus Live Prize/Award
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Sponsoring Units: DSOFT Chair: Douglas Durian, University of Pennsylvania Room: 07 |
Monday, March 15, 2021 11:30AM - 11:42AM Live |
B07.00001: Stokesian Dynamics of Arbitrary-Shape Passive and Active Particles in Linear Flow: Constraint and Rigid Body Approaches Ramzi Kutteh Passive and active small particles present in natural or technological flow-driven processes are typically of arbitrary shape. The physical properties of such processes depend ultimately on the particle dynamics, which in turn is greatly influenced by particle shape through hydrodynamic interactions (HI). We recently extended two complementary approaches for Stokesian Dynamics (SD) simulations of arbitrary shape particles in quiescent fluid, the constraint SD approach[1] and the rigid body SD approach[2], to the presence of linear flow. Either approach models arbitrary shape particles as groups of primary spheres with HI furnished by any desirable mobility algorithm for spheres[3], but whereas the former is effective for any size flexible particles but only small rigid ones, the latter is useful for any size rigid particles. We describe both extended approaches and show SD simulations results from each. |
Monday, March 15, 2021 11:42AM - 11:54AM Live |
B07.00002: Self-assembly of Colloidal Superballs Under Uniform Compression Sarah Schyck, Janne-Meike Meijer, Lucia Baldauf, Andrei Petoukhov, Peter Schall, Laura Rossi Understanding the relationship between colloidal building block shape and self-assembled material structure is important for the development of novel materials by self-assembly. In this regard, colloidal superballs are unique building blocks because their shape can smoothly transition between spherical and cubic. Assembly of colloidal superballs under uniform compression, attained from drying colloidal dispersion droplets on superhydrophobic plates, results in macroscopic opals with ordered internal structures. By utilizing Small Angle X-Ray Scattering (SAXS), we probe the internal structure of the droplets during compression. We identify and observe structure formation before a transition point that arises due to particle dewetting. |
Monday, March 15, 2021 11:54AM - 12:06PM Live |
B07.00003: Formation of a stable colloidal quasicrystal with negligible phason strain Kwanghwi Je, Sangmin Lee, Michael Engel, Sharon C Glotzer Quasicrystals occur in systems comprised of building blocks ranging from atoms to molecules to nanoparticles,suggesting that there are mechanisms for quasicrystal formation and stabilization independent of building block type or size. Yet, mechanisms of quasicrystal formation have only been clearly demonstrated in alloys, where quasicrystals grow imperfectly with phason strain, and only perfect themselves later into a high-quality quasicrystal with negligible strain. Such formation mechanism leading to high-quality quasicrystals has not been reported in other types of quasicrystals, such as soft matter quasicrystals consisting of colloids or polymers. Here, we study the formation of a colloidal dodecagonal quasicrystal (DQC) in a hard tetrahedron system via Monte Carlo simulations. We find that phason strain remains small during DQC growth and only weakly relaxes further, resulting in a high-quality DQC with negligible phason strain directly from the melt. We also observe that a quasicrystal approximant with inherent phason strain transform to the DQC via continuous phason strain relaxation. These results demonstrate that the DQC can be stable over approximants and be grown with high structural quality as in alloy quasicrystals. |
Monday, March 15, 2021 12:06PM - 12:18PM Live |
B07.00004: Phase transitions in colloids under microgravity Boris Khusid, Qian Lei, Lou Kondic, Paul M Chaikin, Andrew David Hollingsworth, Alton Reich, William Meyer Research on colloids is motivated by several factors. They can be used to answer fundamental questions related to the assembly of materials, and they have many potential applications in electronics, photonics, and life sciences. However, the rich variety of colloidal structures observed on the Earth can be influenced by the effects of gravity, which leads to particles settling and the motion of the surrounding fluid. To suppress the gravity effects, experiments on concentrated colloids of spherical and ellipsoidal fluorescent particles were carried out aboard the International Space Station. The particles were suspended in a decalin/tetralin mixture to match the particle refractive index. Confocal microscopy was used to visualize the particle behavior. |
Monday, March 15, 2021 12:18PM - 12:30PM Live |
B07.00005: Determining the size of individual colloidal hard spheres from tracking information Chris Jensen, Brianna Binder, Ryan Watson, J. corwin Coburn, Katharine Jensen In experiments with densely-packed colloidal particles, key material properties like local density, free volume, and elastic modulus depend exquisitely on the precise interparticle separations. However, although it is possible to determine the location of colloidal individual particles with very high precision using confocal microscopy and image analysis, it is usually not straightforward to determine each particle’s size. Recent advances in 3D image processing have made this possible for some colloidal samples, but particle sizing remains a major challenge in many experiments. In this work, we present a new, efficient approach to measuring individual particle radii using linear programming to solve a system of equations derived from closest approach data. We test our algorithm on both simulated and experimentally-measured polydisperse hard-sphere colloidal crystals, glasses, and liquids. We further discuss the sensitivity of our method to noise in the tracking and compare to earlier tracking-based algorithms. |
Monday, March 15, 2021 12:30PM - 12:42PM Live |
B07.00006: Probing the "cage effect" in grain boundary dynamics using impurity particles in a 2D colloidal crystal Ya Chen, Xinlan Tan, Huaguang Wang, Zexin Zhang, John Michael Kosterlitz, Xinsheng Ling Grain boundaries are ubiquitous defects in crystalline solids, yet they are poorly understood. Recently it was reported that grain boundaries in a colloidal crystal exhibit caging effect which was often found in glassy materials. Here, we study the dynamics of grain boundaries in a 2D colloidal crystal of monodispersed microspheres doped with impurities of ellipsoidal particles. As the impurities increase, the long range orientational order of the system is broken and the glassy dynamics of the impurities appears. The cage effect is revealed by the plateau effect in the mean square displacement vs. time curve. We will discuss the possible underlying physics of this “cage effect”. |
Monday, March 15, 2021 12:42PM - 12:54PM Live |
B07.00007: 2D isotropic-nematic transition in colloidal magnetic ellipsoids Xinlan Tan, Ya Chen, Huaguang Wang, Zexin Zhang, Xinsheng Ling Two-dimensional (2D) liquid crystal phase transition is one of the most important issues in condensed matter physics. In contrast to computational work reported in the last few decades, little research has been done in experiments. Anisotropic colloids provide an excellent experimental model system to study phase transitions, such as crystallization and glass transition in condensed matter physics with single particle resolution. However, the corresponding study for the two-dimensional liquid crystal transition remains a challenge, since the condensed anisotropic colloids usually stuck into the metastable glass phase rather than their equilibrium liquid crystal phase. Here we report a colloidal system composed of paramagnetic anisotropic particles that can overcome the free energy barrier from the metastable states towards the equilibrium phase by applying an external magnetic field. The experiments show a 2D isotropic-nematic transition with increasing packing density of the colloidal particles. The transition process is experimentally identified and found to be dependent on the anisotropy of the colloidal particles. |
Monday, March 15, 2021 12:54PM - 1:06PM Live |
B07.00008: Particle Size Disparity Controls Stacking Disorder in Colloidal Assemblies Roger Reinertsen, Sumit Kewalramani, Ali Ehlen, Monica Olvera De La Cruz, Michael J Bedzyk Conventional wisdom in colloidal assembly holds that particle polydispersity prohibits long-range order. However, a thorough experimental investigation connecting the disorder in colloidal packing and particle size-dispersity has remained elusive, likely due to the challenges associated with fabricating colloids with specific size distributions. By functionalizing gold nanoparticle cores with monodisperse synthetic DNA strands of different lengths, anionic particles of tunable size and polydispersity can be fabricated. Using electrolytes to assemble such particles, we analyze size-dispersity effects by tuning: 1. the variance of the continuous particle size distributions and 2. the composition and mean component particle sizes of binary mixtures. Our X-ray scattering studies reveal that the assembly transforms from FCC (face centered cubic) to RHCP (random hexagonal) to random close packed (RCP) as the variance is increased, or as the mixture composition is moved toward equimolarity. Furthermore, stacking disorder continuously increases as the assembled structure moves across these phases. This work provides quantitative insights into the role of size dispersity in colloidal assembly. |
Monday, March 15, 2021 1:06PM - 1:18PM Live |
B07.00009: Flow-induced exfoliation of graphene: understanding colloidal microphysics to produce graphene on the ton scale Lorenzo Botto In liquid-phase exfoliation, microparticles of graphite are suspended in a liquid solvent, and the resulting colloidal dispersion is subject to energetic mixing. At a critical value of the local shear rate, layers of graphene are removed from the mother graphite particles. Liquid phase exfoliation is one of the most important production method for graphene, but its microscopic mechanics is incompletely understood. In this talk I will describe our recent work on the theoretical and computational modelling of liquid-phase exfoliation of graphene/graphite, and discuss how our work differ from related investigation on hydrodynamic breakup of colloidal aggregates. We developed two classes of models: a sliding model for relatively rigid nanosheets (Gravelle, Kamal, Botto J. Chem. Phys. 152(10) 2020) and a peeling model for graphene sheets which are able to bend (Salussolia et al., J. Mech. Phys. Solids. 134, 2020). Key conclusions of our work are that only by invoking stress amplification effects due to flow-induced fracture the predicted critical shear rates can become comparable in order of magnitude with the experimental data, and that current estimations of adhesive forces are affected by inacceptable assumptions. |
Monday, March 15, 2021 1:18PM - 1:54PM Live |
B07.00010: Early Career Award for Soft Matter Research (2020): Molecular Mimetic Colloids: synthesis and assembly. 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. |
Monday, March 15, 2021 1:54PM - 2:06PM Live |
B07.00011: The stresslet for colloidal suspensions confined in a spherical cavity Emma del Carmen Gonzalez Gonzalez, Roseanna Zia Spherically-confined colloidal suspensions are a useful model system for representing a simple biological cell, where macromolecules interact and undergo diffusion, self-assembly, and flow. The microscopic forces between those colloids, including hydrodynamic, Brownian, and interparticle forces, are affected by confinement and thus computational models must represent these effects. In the Stokesian dynamics framework, the fluid-mediated interactions arising from these forces are represented by a hierarchy of hydrodynamic traction moments on particle surfaces. The initial Confined Stokesian dynamics algorithm1,2 paved the way to such computational methods by obtaining the hydrodynamic force and torque in a spherical cavity but was restricted to equilibrium because the stresslet coupling is required to extract suspension viscosity and osmotic pressure. Here we present the exact solution for stresslet hydrodynamic functions of a colloid in a spherical cavity, and its application to more concentrated suspensions via the Confined Stokesian dynamics algorithm. With this algorithm, we predict high-frequency dynamic viscosities as well as osmotic pressure of confined Brownian suspensions. |
Monday, March 15, 2021 2:06PM - 2:18PM Live |
B07.00012: Binary colloidal mixture with maximum packing density Hyo Eun Kim, Byung Mook Weon, Woojun Jeong, GUN OH Evaporative deposition of colloidal nanoparticles or nanoinks is a versatile process for inkjet printing. Typically, using monodisperse colloids, formation of empty spaces and pores between colloidal particles is inevitable in colloidal deposits. Such vacancies act as defects because they degrade physical properties of deposits. To eliminate pores, a polydisperse mixture that consists of large and small colloids is appropriate from theoretical predictions. Here, we examine binary colloidal mixtures to find a condition for maximum packing density in random packing and crystal structures. Particularly, we look into colloidal deposits of binary mixtures with X-ray nanotomography and light holographic microscopy to identify geometric information. Particle size segregation may occurs during evaporation because of Brazil nut effect or osmotic pressure. We show a method to achieve maximized packing density with polydisperse binary mixtures for applications into advanced colloidal nanoinks. |
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