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 C06: Rheology and Flow of Soft MaterialsLive
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Sponsoring Units: DSOFT Chair: Irmgard Bischofberger, Massachusetts Institute of Technology MIT Room: 06 |
Monday, March 15, 2021 3:00PM - 3:12PM Live |
C06.00001: Modelling flow and rheology of Graphene Catherine Kamal, Simon Gravelle, Lorenzo Botto We study theoretically the rotational dynamics and rheology of dilute suspensions of rigid graphene in a simple shear flow. In the infinite Péclet number limit, a rigid platelet with the interfacial hydrodynamic slip properties of graphene does not follow the periodic rotations predicted by Jeffery’s theory, but aligns itself at a small inclination angle αc with respect to the flow. This unexpected result is due to the hydrodynamic slip reducing the tangential friction at the graphene-solvent surface. By analyzing the Fokker-Plank equation for the orientational distribution function for decreasing Péclet numbers, we show that the platelet fluctuates about αc until a slip length dependent critical Péclet number is reached. Below this value, Brownian forces are large enough to induce full rotations. We compare the rheology of the suspension to Molecular Dynamics simulations of graphene-like platelets and show that slip can dramatically change the macroscopic behaviour of the suspension. For example, at large Péclet number, the effective viscosity of a dilute suspension of graphene platelets is predicted to drop by at least a factor of 2 for typical slip length values. |
Monday, March 15, 2021 3:12PM - 3:24PM Live |
C06.00002: Shear Yieldind and Percolation Transition in Smectics Liquid Crystals Livio Nicola Carenza, Giuseppe Gonnella, Davide Marenduzzo, Giuseppe Negro Yielding in complex fluids is a poorly understood phenomenon which consists of a solid-like behavior at low strain rates characterized by a divergent viscosity, while a Newtonian flowing regime is observed at larger forcing. Many amorphous soft materials -such as foams, emulsions and microgels- exhibit yielding behaviors. |
Monday, March 15, 2021 3:24PM - 3:36PM Live |
C06.00003: Rheology of associative telechelic polymer - latex suspension Ethayaraja Mani, Gopal Parthasarathy, Alyssa Travitz, Ronald G Larson We report a computational study on the rheology of latex suspension, where the interparticle interactions are mediated by associative polymers such as hydrophobically-modified ethylene oxide urethane. The polymer is modelled as a FENE dumbbell and the particle as WCA repulsive spheres. Suspension viscosity and normal stress differences are measured from non-equilibrium Brownian dynamics simulation by imposing shear. The microstructure is controlled by polymer dynamics such as bridging (a polymer attaching to two different particles at either ends), looping (both ends of a polymer attaching to the same particle), and dangling (one end of a polymer is attached to a particle while the other end is free). All these polymer dynamics are affected by shear, modifying the microstructure and hence the viscosity. The polymer-latex system shows shear thinning behavior over a range of shear rates, interspaced between two Newtonian regions. The first normal stress difference is found to be positive. Rheology of the suspension is studied for various polymer-latex attractive strengths, a key parameter varied in experiments. By treating polymer and particle degrees of freedom explicitly, we elucidate the dynamics covering a wide range of length and time scales, and their effects on rheology. |
Monday, March 15, 2021 3:36PM - 3:48PM Live |
C06.00004: Structural and rheological properties of Janus colloid-polymer mixtures in dilute solution under shear Yusei Kobayashi, Noriyoshi Arai, Arash Nikoubashman We investigate the structure and rheological properties of dilute colloid-polymer mixtures at rest and under shear via molecular simulations that take into account hydrodynamic interactions. Mixtures of amphiphilic Janus colloids (JCs) and hydrophobic/amphiphilic polymers are considered for various solvent qualities and polymer concentrations. Free polymers, colloidal micelles, and hybrid aggregates coexist in mixtures with slightly hydrophobic homopolymers. As the solvent quality worsens, all polymers aggregate into small droplets, covered and stabilized by the JCs. In mixtures with amphiphilic polymers, we observe the coexistence of free polymers, purely polymeric micelles, and hybrid aggregates. At small shear rates, all mixtures exhibit a Newtonian-like response with intrinsic shear viscosities that are up to two times as large as of pure suspensions of non-adsorbing colloids at the same concentration. Further, the mean aggregation number increases slightly due to the flow-enhanced collision. At larger shear rates, however, the aggregates break up, the polymers align in the flow direction, and the mixtures become shear-thinning. This breakup occurs at stronger shear compared to pure JC suspensions, indicating that the adsorbed polymers reinforce the hybrid aggregates. |
Monday, March 15, 2021 3:48PM - 4:00PM Live |
C06.00005: Memory effects in dense colloidal suspensions Celine Ruscher, Fabrice Thalmann, Pascal Hebraud Understanding the rheological behaviour of dense colloidal suspensions is of huge interest for industrial and technological applications. As they are amorphous yield stress materials, the mechanical response, and in particular the reversibility, depends strongly on the external applied deformation. |
Monday, March 15, 2021 4:00PM - 4:12PM Live |
C06.00006: Amplitude Nanofriction Spectroscopy Antoine Lainé, Andrea Vanossi, Antoine Nigues, Erio Tosatti, Alessandro Siria Friction at the macroscopic scale originates from the mechanical and tribological response of single micro- to nano-scale single contacts. Consequently atomic scale friction rises as an indispensable component for large scale friction understanding as well as for the ever-growing nanotechnology fields. The interfacial sliding dynamics bears several successive live phases: from static pinning, to depinning and transient evolution, eventually ushering in steady state kinetic friction. While standard tip-based atomic force microscopy generally addresses the steady state, the prior intermediate steps are much less explored. We present here an experimental and simulation approach, taking advantage of a high frequency oscillatory imposed strain to obtain a one-shot investigation of all these successive interfacial responses. Few atoms gold contacts sliding on graphite are used to uncover the phenomena that bridge the gap between initial depinning and large speed sliding. Our findings unveil dynamical response reminiscent of thermolubric behavior at very small contact size and superlubric response for contacts larger than the graphic unit cell. The results pave the way to important insights in the understanding of atomic scale time and magnitude dependent rheology. |
Monday, March 15, 2021 4:12PM - 4:24PM Live |
C06.00007: Sliding Friction of Amorphous Asperities on Crystalline Substrates: Scaling with Contact Radius and Substrate Thickness Joseph Monti, Mark Owen Robbins Disorder in the contact between an amorphous slider and a crystalline substrate leads to a cancellation of lateral forces. Atomically flat, rigid surfaces exhibit structural superlubricity, with the frictional stress in circular contacts of radius a vanishing as 1/a. Elasticity allows relative motion of domains on the surface in response to the random interfacial forces. The competition between disorder and elastic deformation is predicted to limit structural suberlubricity and produce a constant frictional stress for a larger than a characteristic domain size λ that depends on the ratio of the shear modulus G to the magnitude of interfacial shear stresses τ0. Extensive simulations of a flat, amorphous punch sliding on a crystalline substrate with different system sizes and G/τ0 are used to test scaling predictions and determine unknown prefactors that are needed for quantitative analysis. For bulk systems, we find an exponential decrease of the large a frictional stress and 1/λ with increasing G/τ0, while the same quantities decrease linearly with increasing G/τ0 for thin free-standing films. These results may help explain the size-dependent friction of nanoparticles and plate-like materials used as solid lubricants. |
Monday, March 15, 2021 4:24PM - 4:36PM Live |
C06.00008: Drying-induced cracking and bending of nanoparticle suspension drops Paul Lilin, Philippe Bourrianne, Irmgard Bischofberger The drying of sessile drops of aqueous nanoparticle suspensions with particle volume fractions >5% leads to the formation of intricate patterns. As water evaporates, a thin deposit of close-packed particles appears at the edge of the drop and grows toward the center, eventually covering the entire wetted area. Interfacial tension prevents air from penetrating inside this particle deposit, causing an outward flow of water from the bulk liquid in the center of the drop to and through the porous deposit at its edge. When the deposit reaches a certain size, radial cracks form in the deposit defining regular petals. The petals bend upwards into a blooming flower. Using poroelasticity theory, we estimate the stress caused by water flowing in the deposit and show that it can predict both the onset of crack formation for various drying conditions and particle volume fractions, and the shape of the petals as they bend. However, scaling considerations between the bending stiffness and the poroelastic torque predict that all petals will bend the same regardless of their thickness, while we observe that thinner petals bend much more. |
Monday, March 15, 2021 4:36PM - 4:48PM Live |
C06.00009: Neutron Spin Echo Spectroscopy at the Spallation Neutron Source Piotr Zolnierczuk, Laura-Roxana Stingaciu, Michael Monkenbusch Neutron spin echo spectroscopy is one of the most powerful techniques to study the dynamics of soft matter [1]. |
Monday, March 15, 2021 4:48PM - 5:00PM Live |
C06.00010: Nanoscale flow field induced by Brownian motion of particles trapped at complex interfaces Mehdi Molaei, Nicholas G Chisholm, Jiayi Deng, John Crocker, Kathleen Joan Stebe The floow field induced by the motion of particles trapped at complex interfaces is nontrivial due to the hydrodynamic coupling of 2D interfacial and 3D bulk systems. We have developed a method to measure nanoscale flow fields around interfacially trapped colloidal particles undergoing pure Brownian motion. By this method, we map the flow field generated by particle displacements, which are decomposed into interfacial hydrodynamic multipoles, including thermally induced force monopole and dipole flows, whose forms differ significantly from their bulk fluid counterparts. Analysis of the detailed flow structures provide key insights essential to understanding the interfacial response and the nature of 2D-3D hydrodynamic coupling. |
Monday, March 15, 2021 5:00PM - 5:12PM Live |
C06.00011: Drying-induced nucleation patterns in confined hyperelastic hydrogels Baudouin Saintyves, Romain Pic, L. Mahadevan, Irmgard Bischofberger In many constrained systems, from paintings to muddy soils, the evaporation of a solvent leads to the formation of complex drying patterns. These patterns are often characterized by brittle straight cracks typical of drying materials with a low characteristic failure deformation. We report novel pattern morphologies that occur during the drying of highly stretchable hydrogels confined between two glass plates. Here, the evaporation front advances by intermittent cavities, which leads to either a disordered or a “worm-like” network structure. We propose a possible mechanism that sets the cavity size, where a balance between elastic and surface energy is expressed by a dimensionless elasto-capillary number. |
Monday, March 15, 2021 5:12PM - 5:24PM Live |
C06.00012: Rheology of glassy and jamming emulsions Cong Cao, jianshan liao, victor breedveld, Eric Weeks We study the rheology of monodisperse and bidisperse emulsions with various droplet sizes (1 -- 2 diameter). Above a critical volume fraction , these systems exhibit solid-like behavior and possess a yield stress. Previous experiments suggest that for small thermal particles, rheology will see a glass transition at ; for large athermal systems, rheology will see a jamming transition at . However, simulations point out that at the crossover of thermal and athermal regimes, the glass and jamming transitions may both be observed in the same sample. Here we conduct an experiment by shearing four oil-in-water emulsions with a rheometer. We observe both a glass and a jamming transition for our smaller diameter droplets, and only a jamming transition for our larger diameter droplets. The bidisperse sample behaves similarly to the small droplet sample, with two transitions observed. Our rheological data fit well with both the Herschel-Bulkley model and the Three Component model. Our results suggest that liquid-solid transitions may depend on the type of particle. |
Monday, March 15, 2021 5:24PM - 5:36PM Live |
C06.00013: Universal properties of creep flow in amorphous solids Marko Popovic, Tom De Geus, WENCHENG JI, Alberto Rosso, Matthieu Wyart Amorphous solids, such as atomic glasses, colloidal suspensions, granular matter or foams, begin to deform plastically when exposed to external stress Σ. Steady state shear flow of these materials, in absence of thermal fluctuations, is usually described as dγ/dt ∼ (Σ − Σc)β for stresses above critical stress Σc and vanishes below it, while in presence of thermal fluctuations flow persists below Σc. The transient plastic deformation, called creep flow, is much less understood despite its importance in practical applications. Creep flow often displays a power-law decay in time dγ/dt ∼ t−ν after which it can either arrest or eventually yield at fluidisation time τf . In recent years various numerical values and laws have been suggested for the exponent ν and fluidisation time τf in particular experimental or numerical studies. We propose that scaling properties of the creep flow are determined by its the steady state flow. This allows us to predict ν and τf characterising the creep flow in terms of the steady state flow parameters, both in athermal and thermally activated systems. We successfully test our predictions using mesoscopic elasto-plastic models of amorphous solids and find them to be consistent with published experimental results. |
Monday, March 15, 2021 5:36PM - 5:48PM Live |
C06.00014: Using acoustic perturbations to tune bouncing on thickening cornstarch suspensions Zhicheng Wang, Meera Ramaswamy, Prateek Sehgal, Ran Niu, Itai Cohen You’ve undoubtedly encountered viral videos on social media showing people walking on pools of cornstarch suspensions without sinking. Such videos illustrate a fascinating property of suspensions: shear jamming under compression. Here, we investigate whether acoustic perturbations are a viable strategy for unjamming suspensions under compression. Specifically, we report on measurements of the coefficient of restitution for steel ball bearings bouncing a cornstarch suspension surface as a function of the impact energy and acoustic power for different weight fraction suspensions. We find that the coefficient of restitution depends sensitively on the weight fraction of cornstarch. In addition, we find that the coefficient of restitution, while constant for low impact energies, decreases at high impact energies as 1/impact energy. This decrease suggests an upper limit to the suspension elasticity. Finally, we demonstrate that acoustic perturbations can indeed change the coefficient of restitution, indicating this is a viable strategy for unjamming and, perhaps, making people sink on command as they walk across a pool filled with cornstarch suspension. |
Monday, March 15, 2021 5:48PM - 6:00PM Live |
C06.00015: Elasticity in dense suspensions of geometrically frustrated colloids Shravan Pradeep, Alan Wessel, Lilian Hsiao The elastic component of the stress response in dense colloidal suspensions is determined by the evolution of local microstructure, especially for frictional particles with surface asperities. For frictionless particles interacting through a hard-sphere potential, the storage modulus (G’) of the suspension scales with the particle diameter (2a) as 1/a3. However, this scaling does not necessary hold for rough particles at high Φ. We suspend smooth and rough poly(methyl methacrylate) colloids with diameters 2a = 1.50 μm ± 6% and 2aeff = 1.55 μm ± 5% respectively in a refractive index matched solvent, squalene. The aim is to study the effects of surface roughness and packing on the viscoelastic modulus. Frequency-sweep rheometry show that changes in the scaled modulus occurs as a function of the scaled jamming distance Φ* = ΦJ-Φ/ΦJ and with particle roughness. Close to jamming (Φ* < 0.2), the smooth particle suspensions exhibit a scaled modulus in the O(10 Pa) while rough particle suspensions exhibit a modulus in the O(105 Pa). The data suggest that there is a direct link between the energy dissipation and the geometric frustration of particles that exhibit rotational constraints due to surface roughness. |
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