Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session K05: Dillon Medal SymposiumFocus
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Sponsoring Units: DPOLY Chair: Wesley Burghardt, Northwestern University; Ali Dhinojwala Room: Room 128 |
Tuesday, March 7, 2023 3:00PM - 3:36PM |
K05.00001: John H. Dillon Medal (2022): Stretched Polymer Physics and Rheology Invited Speaker: Vivek Sharma Stringiness, stickiness, and dispensing behavior of polymeric complex fluids are often assessed qualitatively by dripping from a nozzle or spoon or by stretching a liquid bridge between two surfaces (thumb and forefinger). Here the lifespan of pinching necks is determined by the response of polymers to extensional flows associated with streamwise velocity gradients that spontaneously arise within necks undergoing capillarity-driven thinning. Here we describe dripping-onto-substrate (DoS) rheometry protocols we developed to facilitate extensional rheology characterization even for lower viscosity fluids and at high extensional rates beyond the range of most commercially-available methods. Using DoS rheometry protocols, we pursue various intertwined quests in stretched polymer physics including conformation-dependent hydrodynamic and excluded volume interactions, Pincus’ tension blobs, finite extensibility effects, as well as coil-stretch transition and hysteresis. We observe that the extensional relaxation times exhibit concentration-dependent variation distinct from shear rheology response measured using shear rheometry or anticipated by blob models developed for the relaxation of weakly perturbed chains. We show that the influence of molecular weight and chemistry can be evaluated a priori using three macromolecular parameters: flexibility, extensibility, and segmental dissymmetry for neutral polymers. Finally, we characterize and analyze the pinch-off dynamics of charged polymers to elucidate the influence of the complex interplay of electrostatic and hydrodynamic stretching of macromolecules and demonstrate how the changes in salt or solvent influence stretched polymer physics. We identify the stretched overlap concentration below which the extensional relaxation time is concentration-independent and a spinnability concentration (below which only beads but no fibers appear) by accounting for the influence of higher extensibility of ultrahigh molecular weight fractions. |
Tuesday, March 7, 2023 3:36PM - 3:48PM |
K05.00002: Adventures of a curious scientist: Self-Assembly of Water Drops to Optics of Butterflies and Beetles Mohan Srinivasarao In our studies we focus on the physics and chemistry of soft condensed matter, materials that are easily deformed by external forces; external stresses, electric or magnetic fields and not to mention thermal fluctuations. Typical materials that are considered to encompass soft matter include liquid crystals, colloids, and polymer solutions along with a host of biological materials. Such materials possess structures which are much larger than atomic or molecular scales; the structure and dynamics at mesoscopic scales determine the physical properties of these materials. We use optical methods, mostly various forms of light microscopy and scattering to study and understand such soft materials. In this talk, I will provide two such examples using structure formation in polymer solutions and structural color in biology. These were things, the Dillion Award winner for 2023, worked on while a student at the Georgia Institute of Technology |
Tuesday, March 7, 2023 3:48PM - 4:00PM |
K05.00003: The Fluid Dynamics of Dripping onto a Substrate (DOS) Gareth H McKinley, Konstantinos Zinelis, Thomas Abadie, Omar K Matar Extensional flows of complex fluids are important in many industrial applications such as spraying, atomization, and microfluidic-based drop deposition. The Dripping-on-Substrate (DoS) technique pioneered by the Sharma ODES Lab is a conceptually-simple, but fluid dynamically complex, probe of the extensional rheology of low viscosity non-Newtonian fluids. It incorporates the capillary-driven thinning of a liquid bridge, produced by a single drop as it is dispensed from a syringe pump onto a partially-wettable solid substrate. By following the filament thinning process, the extensional viscosity and relaxation time of the sample can be determined. Importantly, it allows rheologists to measure the extensional properties of lower viscosity materials than is possible with commercially-available capillary break-up extensional rheometers. Understanding the fluid mechanics behind the operation of DoS will allow us to optimize and extend the application of this protocol. We employ a computational rheology approach using adaptively-refined axisymmetric numerical simulations with the open-source Eulerian code, Basilisk. The volume-of-fluid technique is used to capture the moving interface, and the log-conformation transformation provides a stable and accurate solution of the viscoelastic constitutive equation. We explore the role of elasticity and polymer finite extensibility on controlling the Elasto-Capillary (EC) regime, as well as the perturbative effects that gravity and the wetting of the solid substrate play in setting the evolution of the self-similar thinning and pinch-off dynamics. To illustrate the interplay of these different forces we construct a simple nonlinear one-dimensional model that can capture the initial rate of thinning, when the interplay of inertia and capillarity dominates, as well as the structure of the transition region to the non-linear EC regime where the rapidly growing elastic stresses in the thread balance the capillary pressure as the filament thins towards breakup. |
Tuesday, March 7, 2023 4:00PM - 4:12PM |
K05.00004: Megasupramolecules take to water Julie A Kornfield, Red Lhota, Robert Learsch, Hojin Kim, Chris Nelson Ultralong linear polymers at low concentration profoundly alter the behavior of low viscosity liquids in flows that involve elongation---yet leave the shear viscosity and interfacial tension nearly unchanged. The advent of dripping-on-substrate extensional rheometry (DoSER) represents a major contribution to characterizing these low shear viscosity solutions. One of the key features of ultralong polymers is their susceptibility to irreversible degradation in extensional flow: DoSER proved to be a fast measurement that quantitatively correlates with molecular weight determined by gel permeation chromatography (GPC) for the present systems (long, flexible polymers with 30,000 or more backbone atoms at c/c* of 0.2 to 2 in an inertio-capillary solvent with Ohnesorge number Oh << 1). To overcome irreversible chain scission, we examine long end-associative polymers that can link into ultralong supramolecules, “megasupramolecules.” Individual molecules of 860kg/mol polyacrylamide (PAM) are long, yet their aqueous solutions resist chain scission. Installing terpyridine groups at each end allows them to assemble pairwise by metal-ligand interactions. In strong flows, these pairs dissociate before the force reaches levels that break covalent bonds. DoSER sensitively detects supramolecules, showing that a 0.1%wt solution of 860k terpy-PAM with Ni2+ 1:2 terpy behaves like a 0.1%wt 5.5M PAM homopolymer, hence the name megasupramolecules. |
Tuesday, March 7, 2023 4:12PM - 4:24PM |
K05.00005: Single Molecule Polymer Physics in 3D Flows Charles M Schroeder, Hung V Nguyen Single polymer dynamics is a powerful approach to understand the nonequilibrium behavior of polymers in flow, revealing molecular subpopulations that are otherwise hidden in ensemble-level measurements. Despite recent progress, prior work has nearly exclusively focused on polymer dynamics in two-dimensional (2D) flows generated in planar microfluidic geometries. Here, we extend nonequilibrium dynamics of single polymers and soft materials to 3D flow fields, including uniaxial and biaxial extensional flow. Single polymers and colloidal particles are trapped and manipulated in 3D using automated flow control. Trap stiffness is experimentally determined by analyzing the power spectral density of particle position fluctuations in 3D flows. In addition, single colloidal particles are precisely manipulated along long-distance user-defined trajectories in 3D using active feedback control. Using a simultaneous dual orthogonal-plane imaging technique, the center-of-mass position of single particles is precisely tracked in space during active manipulation in 3D. We further apply the active 3D flow control method to study the nonequilibrium dynamics of single polymers in uniaxial and biaxial flow. Our results reveal fascinating dynamics of single ring polymers and linear polymers in biaxial extension, including both transient and steady-state stretching dynamics in flow. Ring polymers are found to exhibit differences in the coil-to-stretch transition in planar 2D versus 3D extensional flows due to a coupling between chain architecture, flow character, and intramolecular hydrodynamic interactions (HI). Overall, this work extends the nonequilibrim dynamics of single polymers, particles, and soft materials to three dimensions, enabling quantitative analysis of soft materials in complex flow fields. |
Tuesday, March 7, 2023 4:24PM - 4:36PM |
K05.00006: Nonlinear Relaxation of PVA/Borax Solution under Step Strain Hiroshi Watanabe, Yanjie Zhang, Quan Chen Aqueous solutions of poly(vinyl alcohol) (PVA) and Borax exhibit significant viscoelasticity because of association of PVA chains. In unentangled PVA solutions with a high Borax concentration CB, the chains formed a percolated transient network bridged by Borax ions thereby exhibiting sticky Rouse-type LVE relaxation much slower than the relaxation of the neat PVA solution. This high-CB solution showed nonlinear damping under large step strain γ, and its nonlinear relaxation modulus G(t,γ) was time-strain separable at long time (t). The γ dependence of its damping function h(γ) = G(t,γ)/G(t,0) was stronger than that of the unentangled neat solution but weaker than the Doi-Edwards-type γ dependence commonly observed for entangled polymers. This nonlinear damping of the high-CB PVA/Borax solution was analyzed on the basis of the sticky Rouse model wherein the dynamic bridges between chains are treated as beads with a high friction. It appeared that the Rouse-type chain dynamics itself is not affected by the strain but the initial chain conformation just after imposition of the strain changes through the strain-induced disruption of the bridges followed by rapid and (almost) isotropic reformation. In fact, h(γ) calculated from the model with this initial conformation was in good agreement with the h(γ) data, suggesting a simple but unexplored nonlinear damping mechanism of the PVA/Borax solution. |
Tuesday, March 7, 2023 4:36PM - 4:48PM |
K05.00007: Capillary Bonding of Membranes by Viscous Polymers: Infiltration Kinetics and Mechanical Integrity of the Bonded Polymer/Membrane Structures Yifu Ding, Jaylene Martinez, Rong Long, Jason Killgore, Christina Carbrello, Robert Castro, Shouhong Fan, Yinan Lu, Salil Rabade, Stefano Berti, Adrienne Blevins, Sean Foley, Kieran Fung Capillary infiltration of porous medium impacts applications across oil recovery and hydrology. The infiltration kinetics is typically captured by a range of models that differ in the approximation of pore structures, fluid properties, and filling ratio. Capillary bonding of a porous membrane by a polymer melt is important for membrane device manufacturing. However, both the capillary infiltration kinetics and the resulting bonding strength or mechanical integrity have not been reported. In this talk, we present capillary infiltration study of a viscous polypropylene (PP) within polyethersulfone (PES) membranes. The infiltration kinetics was determined under varying infiltration temperature, membrane chemistry and pore structure (pore size and degree of asymmetry). The experimental data was better described by models such as the Cai model that incorporates membrane pore structures, compared with the basic Lucas Washburn model commonly used for isolated cylindrical pores. The mechanical integrity of the bonded PP/membrane structures was further evaluated with a modified T-peel test, displaying a range of debonding or failure behaviors that are dependent on the pore size and infiltration depth. |
Tuesday, March 7, 2023 4:48PM - 5:00PM |
K05.00008: Theory of dipole-driven self-assembly of charged macromolecular aggregates Murugappan Muthukumar We will present a general theory for the spontaneous formation of finite-sized aggregates in solutions of polyzwitterions, physical polyzwitterions, polyelectrolytes, and intrinsically disordered proteins. Accounting for electrostatic and topological correlations, ionization equilibria, Donnan equilibrium, and elasticity, we have derived a universal law for the size of the aggregates in terms of the experimental variables such as polymer concentration, temperature and solvent quality, and salt concentration. In addition, the thermodynamic stability of these aggregates will be addressed in the context of the confluence from gelation, microphase separation, and macrophase separation. |
Tuesday, March 7, 2023 5:00PM - 5:12PM |
K05.00009: Influence of Sequence Charge Pattern on Secondary Structures of Bioinspired Polyampholytes Matthew V Tirrell, Jelena Dinic, Mathew Schnorenberg A systematic investigation of the influence of sequence charge pattern on the secondary structure preferences of peptide-based polyampholytes and their responsiveness to external stimuli will be presented. The polyampholyte sequences utilized in this study are composed entirely of ionizable amino acids (charge fraction, f=1), and an equal number of positive and negative charges (f+=f-=0.5) with distinct charge patterns consisting of lysine and glutamic acid monomers. Our work reveals that the sequence charge pattern has a pronounced influence on the secondary structure preferences of polyampholytes at physiological pH. Furthermore, it demonstrates that external stimuli such as pH and ionic strength can be used to modulate the secondary structure of the examined polyampholytes. The observed structural transformations are different from those determined for uniformly charged homo-polypeptides under matching conditions. |
Tuesday, March 7, 2023 5:12PM - 5:24PM |
K05.00010: Salt Weakens Intermicellar Interactions and Structuring in Bulk Solutions and Foam Films Samanvaya Srivastava, Vivek Sharma, Shang Gao, Chrystian Ochoa Ultrathin foam films containing supramolecular structures like micelles in bulk and adsorbed surfactant at the liquid-air interface undergo drainage via stratification. At a fixed surfactant concentration, the stepwise decrease in the average film thickness of a stratifying micellar film yields a characteristic step size. In this presentation, we will contrast these step sizes obtained from the analysis of nanoscopic thickness variations in thin foam films using interferometry protocols with the intermicellar distances in bulk surfactant solutions obtained using small-angle X-ray scattering (SAXS) measurements. In the absence of added salt, the step size in thinning films equals the intermicellar distance in bulk solutions obtained from SAXS experiments. However, this analogy will be shown to break down with the addition of salt. Adding salt will be shown to result in a significant reduction in long-range correlations between micelles and smaller intermicellar distances. Weakened long-range correlations also diminish the magnitude, periodicity, and decay length of the oscillatory disjoining pressure leading to smaller step sizes, fewer steps, and rich nanoscopic topography. We infer that the coupling between free surface shape, flows, and structuring within stratified foam films and changes in micellar shape, size, and interactions upon salt addition influence the step size in stratified films and result in the breakdown of the step size - intermicellar distance analogy. |
Tuesday, March 7, 2023 5:24PM - 5:36PM |
K05.00011: Pinching Dynamics of Dense Colloidal Suspensions with Depletion Attractions Jacinta C Conrad, Diego D Soetrisno, Carina D Martínez Narváez, Mariah J Gallegos, Vivek Sharma The macromolecular properties of polymers have a significant effect on their rheological response under extensional flow. Polymers are often added to concentrated particulate suspensions in applications such as 3-D printing, but how they affect the extensional rheology of the mixtures is still incompletely understood. We study the extensional flow properties via the pinch-off dynamics of both polymer solutions and concentrated colloidal suspensions (volume fraction Φ ≥ 0.40) with induced depletion interactions using a dripping-onto-substrate (DoS) protocol. We use a model colloidal system of methacrylate copolymer particles with acrylamide copolymer brushes suspended in a refractive index and density matched mixture of glycerol and water. Depletion attractions between the colloids are introduced by adding polyacrylamide polymers of various molecular weight and dispersity. We characterize the extensional properties by calculating the extensional relaxation time λE from the filament-thinning dynamics. The dependence of λE on polymer concentration becomes stronger with increasing polymer size. Addition of polymers to concentrated particle suspensions delays and modifies the pinch-off dynamics accordingly. Our results suggest that we can tune the processability of concentrated suspensions by varying the size and dispersity of polymer additives. |
Tuesday, March 7, 2023 5:36PM - 5:48PM |
K05.00012: Impact of Photoactive Monomer Location in Photo-responsive Block Copolymer/Ionic Liquid Solutions Timothy P Lodge, Claire Seitzinger By incorporating a photoactive moiety into a block polymer, the phase behavior can be controlled with light. Here we study the effect of the positioning of pendant azobenzene groups along the polymer backbone on the lower critical disorder-order transition of poly(methyl methacrylate)-block-poly(benzyl methacrylate) (PMMA-b-PBnMA, or MB) in the ionic liquid 1,3-dimethyl imidazolium bis(trifluoromethylsulfonyl)imide. By using small angle X-ray scattering and UV-irradiated small amplitude oscillatory shear rheology, the placement of azobenzene statistically along the benzyl methacrylate backbone (MBsA) is compared to locating it as a midblock between the PMMA and the PBnMA (MAB) or as an end block after the PBnMA (MBA). Two concentrations of polymer in the ionic solvent were studied, 35 and 50 wt%. MBsA was also the only sample of the three to successfully transition reversibly between order and disorder with light. Adjusting the position of the azobenzene within the thermo- and photo-responsive polymer solution significantly changes the overall behavior of the solutions and the ability to control that behavior with light and temperature. |
Tuesday, March 7, 2023 5:48PM - 6:00PM |
K05.00013: Viscoelastic Response of Mucus above Living Bronchial Epithelial Cells Gerald G Fuller, Maggie Braunreuther Mucus that lines the lungs acts as the primary defense against inhaled foreign particles and infectious agents by trapping the invaders and preventing them from penetrating the cell layer. Effective mucus clearance, and thus removal of the trapped invaders, is vital for healthy airway function. Asthma is a chronic inflammatory disorder that results in mucus hypersecretion. Over time, this chronic lung inflammation and mucus accumulation can lead to mucus plug formation in the airway, a primary cause of death in patients with asthma. Inflammatory cytokine IL-13, a major mediator of asthma, induces mucin MUC5AC secretion. While increased concentration of MUC5AC has been shown to inhibit mucociliary clearance, the mechanism of mucus transport impairment remains unclear. Thus far it has not been feasible to measure mucus properties on live cells as it is produced by the epithelial cell layer, neglecting the relationship between the physiological environment and mucus rheology. A new instrument, the “Magnetic Live Cell Rheometer”, recently developed by the Fuller group has been adapted to examine mucus rheology in situvia magnetic microrheology. Human airway epithelial cells (HAECs) are grown in air-liquid interface (ALI) cultures, mimicking the airway surface environment. During rheological experiments, we maintain cells at ALI and use micron scale magnetic wires (microwires) to probe the properties of the mucus layer. We apply and remove a magnetic force and track microwire displacement to determine the compliance and viscosity of healthy and IL-13 stimulated mucus on the respective HAEC cultures. We then test existing mucoactive drugs designed to reduce the elasticity and viscosity of the mucus layer to establish correlation with clinical response and rheological measurements. With this method, we demonstrate the ability to study mucus rheology in a physiologically relevant environment, examine phenotypic differences in mucus rheology, and rapidly test drugs on mucociliary mechanics. |
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