Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session J31: Workshop: Grand Challenges in Soft Matter and Opportunities for Microgravity ResearchFocus
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Sponsoring Units: DSOFT Chair: Paul Chaikin, New York University Room: 503 |
Tuesday, March 3, 2020 2:30PM - 3:06PM |
J31.00001: Hot topics and lukewarm opportunities for soft matter science up in the sky Invited Speaker: Roberto Piazza I will first discuss some topics in soft matter that truly deserve to be investigated in microgravity conditions, focusing in particular on spontaneous restructuring processes in colloidal gels, referring to our recent experience with the NASA ACE T10 mission too, and on thermal forces in complex fluids. I shall then present the new opportunities given by the ESA COLIS facility for optical correlation spectroscopy to be installed on the ISS in a couple of years. Finally, however, I shall also point out some limiting factors that tend to cool my enthusiasm towards space experiments in our field. |
Tuesday, March 3, 2020 3:06PM - 3:42PM |
J31.00002: Non-equilibrium behaviour of colloidal systems. Invited Speaker: Daan Frenkel There is an explosion of interest in the collective properties of active matter. This interest is understandable because it is exciting to step outside the confines of the classical statistical mechanics that was developed to describe systems at or near equilibrium. |
Tuesday, March 3, 2020 3:42PM - 4:18PM |
J31.00003: Squeezing order out of disorder Invited Speaker: Stefano Martiniani Computable Information Density (CID), the ratio of the length of a losslessly compressed data file to that of the uncompressed file, is a measure of order and correlation in both equilibrium and nonequilibrium systems. I will show that correlation lengths can be obtained by decimation, thinning a configuration by sampling data at increasing intervals and recalculating the CID. When the sampling interval increases above the system’s correlation length, correlations vanish and the data becomes incompressible. The correlation length critical exponents are thus accessible with no a-priori knowledge of an order parameter or even the nature of the ordering. The critical scalings for the length scales obtained by CID agree well with those from the decay of two-point correlation functions g2(r) when they exist. But CID also reveals a correlation length with the right scaling when g2(r) = 0, as we demonstrate by “cloaking” the data with a Rudin-Shapiro sequence. Finally, I will show how CID revealed previously unknown ordering phenomena, such as a cascade of phase transitions in the BML traffic model, and a "checkerboard" dynamical instability in the parallel update Manna sandpile model. |
Tuesday, March 3, 2020 4:18PM - 4:30PM |
J31.00004: ESA microgravity program for Soft Matter research Marco Braibanti The International Space Station offers a unique environment to study Soft Matter systems, which are susceptible to the effect of gravity. |
Tuesday, March 3, 2020 4:30PM - 4:42PM |
J31.00005: Electric field driven aggregation of negatively and positively polarized particles in dilute suspensions Boris Khusid, Qian Lei, Ezinwa Elele A variety of colloidal structures observed in terrestrial experiments could also have been influenced by gravity effects (particle sedimentation, convection, etc.) It is often assumed that weightlessness simulated in a time-averaged sense by slowly rotating a specimen in a clinostat about an axis perpendicular to the gravity direction that is widely used in biological tests would reduce the effect of gravity on suspensions. Experiments on a non-buoyancy-matched suspension in flights in NASA Zero-gravity aircraft revealed that particle patterns formed in a clinostat and under normal gravity are actually similar. A requirement for matching densities between particles and a solvent severely limits possibilities to study the field-induced structuring in colloids in terrestrial experiments. Long-term microgravity in ISS offers unique opportunity to employ not density matched suspensions to explore a wide range of the mismatch of electric characteristics between particles and a solvent. We will report experimental data on the field driven structure formation in suspensions and present our approach to the development of ISS experiments. The aim is to understand mechanisms of structure formation and suggest novel routes for creating functional materials. |
Tuesday, March 3, 2020 4:42PM - 4:54PM |
J31.00006: Structure and dynamics of a two-dimensional colloid of liquid droplets Christoph Klopp Free-standing liquid crystal bubbles were prepared in microgravity on the International Space Station (ISS) in order to study the hydrodynamics of inclusions in quasi 2D fluid systems [1]. The layered structure in of smectic A and C phases allows the preparation of thin and homogeneous films. Arrays of droplets of molten film material can be formed near the clearing point when the inner layers of the film melt and the film undergoes thinning transitions. The droplets interact repulsively with each other, they spontaneously forming nearly approximately regular triangular lattices in smectic A films, with short range positional order. Local lattice cell parameters depend on droplet sizes. These structures can be considered as genuine, two-dimensional (2D) colloidal crystals. We investigate the internal dynamics in these lattices [2]. The mobility of each droplet in its six-neighbor cage is determined by the ratio of cage and droplet sizes, rather than by the droplet size as in isolated droplets. |
Tuesday, March 3, 2020 4:54PM - 5:06PM |
J31.00007: Shapes and forms for 2D liquid crystal materials Zhengdong Cheng, Dali Huang, Ugochukwu Okeibunor <p style="margin: 0px 0px 10.66px;"><font color="#000000" face="Calibri" size="3">Anisotropic 2D colloids can show a plethora of liquid crystalline phases including nematic, columnar and smectic. Due to the ability to control the shape and forms, zirconium phosphate nanoplates have been utilized as a model system. We will discuss the challenges for controlling the size, shape and forms of 2D materials in general. <span style="margin:0px"> </span>We also present results on control of their self-assembly using external fields including shear, electromagnetic, optical, temperature gradient and gravity.</font></p> |
Tuesday, March 3, 2020 5:06PM - 5:18PM |
J31.00008: Model hard ellipsoids: the practical matter of producing them Andrew Hollingsworth, Paul M Chaikin, Lou Kondic, Alton Reich, Boris Khusid Model hard colloids have a great deal of relevance to physics and in particular the study of their phase behavior which can mimic that of simple atomic liquids and solids. "Nearly hard colloidal sphere" suspensions were formulated 35 years ago by the Ottewill group (Univ. of Bristol) and Imperial Chemical Industries Ltd., which were used by Pusey and van Megen in their seminal study of the phase behavior of hard-sphere colloids. We report on our efforts to reproduce and refine this benchmark polymer colloid, including the recent synthesis of hard ellipsoids for random and ordered packing studies in microgravity*. The custom-made samples are composed of linear polymer chains of poly(methyl methacrylate), functionalized with photo-crosslinkable moieties and fluorescent molecules. The resulting ellipsoidal shapes are about 1 micron in size and stabilized with surface-grafted poly(12-hydroxystearic acid) chains. The particles are dispersed in a refractive index matching fluid and particle aspect ratios vary from 1 to 4. |
Tuesday, March 3, 2020 5:18PM - 5:30PM |
J31.00009: Coarsening of two-dimensional island emulsions on smectic liquid crystal bubbles in microgravity Cheol Park, Eric Minor, Joseph E MacLennan, Matthew Glaser, Noel Anthony Clark, Christoph Klopp, Torsten Trittel, Ralf Stannarius Two-dimensional island emulsions in molecularly thin, tethered smectic liquid crystal bubbles in microgravity are observed to coarsen via coalescence and Ostwald ripening in both the smectic A and smectic C phases. We report here on the observed dynamics of island growth and disappearance in the absence of coalescence at locations in the island emulsion far from the meniscus around the bubble inflation needle. This Ostwald ripening occurs as a result of the system’s tendency to reduce its energy through a decrease in the total length of the island boundaries, a process that is generally dependent on the surface and line tensions and the disjoining pressure of the islands. Smaller islands generally have a higher disjoining pressure than their larger neighbors, which results in permeative flow from the smaller to the larger islands. We will also describe emulsion coarsening by island coalescence and compare the experimentally observed coarsening dynamics with simulations. |
Tuesday, March 3, 2020 5:30PM - 5:42PM |
J31.00010: Temperature-gradient-induced thermomigration in smectic liquid crystal bubbles and freely suspended films in microgravity Noel Anthony Clark, Cheol Park, Eric Minor, Joseph E MacLennan, Matthew Glaser, Torsten Trittel, Alexey Eremin, Kirsten Harth, Ralf Stannarius In-plane temperature gradients were applied to tethered smectic bubbles on the ISS during the OASIS mission and to thin freely-suspended smectic films during suborbital rocket flights in order to study the Marangoni effect in a 2D fluid in microgravity. Tethered bubbles of smectic A liquid crystal were inflated in a temperature-controlled chamber. An emulsion of islands subsequently generated on the bubble with an air jet was initially homogeneously distributed over the entire bubble surface. When the inflation syringe was heated, however, the islands moved away from the point of heating, with the island velocity decreasing as they migrated away from the syringe. The islands appear to be moving with the background film, not as a direct consequence of the thermal gradient. In flat films, on the other hand, in-plane temperature gradients were observed to cause two specific Marangoni effects, directed flow and convection patterns. |
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