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 P05: Emulsions and FoamsLive
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Sponsoring Units: DSOFT Chair: John Crocker, University of Pennsylvania Room: 05 |
Wednesday, March 17, 2021 3:00PM - 3:12PM Live |
P05.00001: Passive Microrheology of Strongly Attractive Dense Emulsions using Diffusing Wave Spectroscopy Yixuan Xu, Frank Scheffold, Thomas G Mason We make diffusing wave spectroscopy (DWS) measurements of dense, oil-in-water, size-fractionated, colloidal emulsions having strong short-range interdroplet attractions of ~15 kBT caused by micellar depletion. This strong slippery attraction significantly alters the mean free path of optical transport, l*, compared to nearly hard interactions, and complicates the interpretation of fundamental scattering objects that are associated with DWS self-motion mean square displacements (MSDs), even after accounting for collective scattering. We develop an opto-mechanical decorated core-shell network (DCSN) model to determine an effective radius of the DWS probes by analyzing the measured l*(φ) over a wide range of droplet volume fractions, φ, above and below the hard-sphere jamming point. Using this effective radius and the measured long-time plateau self-motion MSDs, both obtained optically, we show that the generalized Stokes-Einstein relation (GSER) of thermal-entropic passive microrheology yields microrheological plateau elastic shear moduli which are in quantitative agreement with mechanical rheometry. |
Wednesday, March 17, 2021 3:12PM - 3:24PM Live |
P05.00002: Generating oil-in-water Pickering emulsions in PDMS to synthesize plasmonic mechanochromic microcapsules Sean Choe, Remi Dreyfus, Jacques Leng Oil-in-water (o/w) Pickering emulsions stabilized by gold nanoparticles (AuNPs) were synthesized using polydimethylsiloxane (PDMS) chips. These emulsions serve as the basis of a mechanochromic microcapsule (MC) with AuNPs at their surface. Exterior stimuli such as mechanical strain or pH induce a conformational change in the MCs, and thus a change in plasmonic resonance exhibited by the AuNPs. Emulsification by ultrasonication having been proven successful [1][2], we plan to synthesize MCs via microfluidics as it allows relative ease of control of the process and in situ observation of emulsification. PDMS, widely used in microfluidics, is not considered suitable for o/w emulsification. Here we present microfluidic experiments carried out in search of optimal conditions for stable o/w Pickering emulsions in PDMS. |
Wednesday, March 17, 2021 3:24PM - 3:36PM Live |
P05.00003: Spreading of a 2D granular analogue of a liquid puddle: Predicting structure through a “granular capillary length” Johnathan Hoggarth, Jean-Christophe Ono-dit-Biot, Kari Dalnoki-Veress The structure of an accumulation of granular material, such as a pile of sand, can be characterized by the angle of repose, which is dependent on the balance between gravity and inter-grain friction. In contrast, for the case of a continuous medium, the height of a puddle is dictated by the capillary length which balances gravity and surface tension. Here we present an experiment that allows us to probe the structure of a 2D pile of monodisperse microscopic oil droplets. The droplets are buoyant, adhesive, and friction is negligible. Oil droplets are deposited within a chamber and accumulate at a barrier under the influence of buoyancy. The droplets reach a critical height and spread across the barrier. This process is reminiscent of the spreading of a liquid puddle, even though the pile is granular and 2D in nature. We define a parameter, analogous to the capillary length, which controls the height of the pile and is determined by the balance between buoyant and adhesive forces. These forces can be controlled experimentally to modify the height of the pile. We developed a model that can predict the shape of the pile based on the balance of adhesion and buoyancy. |
Wednesday, March 17, 2021 3:36PM - 3:48PM Live |
P05.00004: Characterizing emulsion formation in Absinthe as a function of temperature Jessica Bickel, Anna Ellis, Andrew H Resnick Oil flavored alcohols are traditionally served by mixing them with cold water to form a louche: a microemulsion that turns the drink turbid, sometimes also referred to as the “ouzo effect”. Formation of the louche depends on the relative concentrations of water, ethyl alcohol and oil. Although the ouzo effect has been studied in ouzo and limoncello, it has not been characterized in absinthe. Previous work demonstrated distinct differences between ouzo and limoncello. Also, little has been done to examine the role of temperature in the louche. Our work examines the emergence of the louche phase in absinthe by measuring the optical transmittance of the solution as a function of ethanol concentration at multiple temperatures. Optical transmission was measured through a temperature-controlled sample of absinthe and the change in transmission, accompanied by formation of the louche, was recorded as water was added to the sample, revealing an inverse relationship between temperature and critical ethanol concentration at which louche forms. The transition from clear solution to louche is an s-shaped curve and by fitting this with a sigmoid function we have determined that louche formation is a first-order phase transition. |
Wednesday, March 17, 2021 3:48PM - 4:00PM Live |
P05.00005: Continuum model applied to granular analogues of droplets and puddles Jean-Christophe Ono-dit-Biot, Tanel Lorand, Kari Dalnoki-Veress We investigate the growth of aggregates made of adhesive frictionless oil droplets, piling-up against a solid interface. Monodisperse droplets are produced one-by-one in an aqueous solution and float upwards to the top of a liquid cell where they accumulate and form an aggregate at a flat horizontal interface. The horizontal spreading of aggregates along the interface results from sudden discrete avalanches. Initially, the aggregate grows in 3D until its height reaches a critical value. Beyond a critical height, adding more droplets results in the aggregate spreading in 2D along the interface with a constant height. We find that the shape of such aggregates, despite being granular in nature, is well described by a continuum model. The geometry of the aggregates is determined by a balance between droplet buoyancy and adhesion as given by a single parameter, a granular capillary length, analogous to the capillary length of a liquid. The continuum model presented well explains the average growth rate of the aggregates, while the avalanches, which result in discrete growth steps, are a signature of the underlying granular nature of the aggregates. |
Wednesday, March 17, 2021 4:00PM - 4:12PM Live |
P05.00006: Exploring energy landscapes experimentally via hyper-dimensional tracking in a ripening emulsion Clary Rodriguez-Cruz, Amruthesh Thirumalaiswamy, Mehdi Molaei, Robert Riggleman, John Crocker Many different soft materials, such as soap foams, mayonnaise, toothpaste and living cells, are known to exhibit similar viscoelastic properties. Their behavior has been recently related to the geometrical properties of their energy landscapes, which evolve due to Ostwald ripening and provide an abstract description of the systems’ total energy function spanning a high-dimensional configuration space. Simulations show that these energy landscapes resemble those around river canyons, having a fractal and highly tortuous structure. Here we experimentally demonstrate the ability to explore the geometry of these high-dimensional energy landscapes, using mayonnaise-like dense emulsion droplets amenable to confocal microscopy. We observe super-diffusive particle motion and large cooperative particle rearrangements, or avalanches, as well as a power-law rheology exponent that corresponds to the fractal dimension of the path taken by the system. Closer examination of avalanche behavior reveals that the canyons that the system follows are distributed uniformly in angle over roughly 30-dimensional subspaces. These findings suggest that such hyper-dimensional exploration may find application in the study of other systems with similar dynamics, such as cytoskeleton networks or stock indices. |
Wednesday, March 17, 2021 4:12PM - 4:24PM Live |
P05.00007: Dynamic and Structural Heterogeneity of a Jamming Emulsion System Xin Du, Eric Weeks
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Wednesday, March 17, 2021 4:24PM - 4:36PM Live |
P05.00008: Coarsening Behavior and Coarsening Induced Rearrangements in Very Wet Quasi-2d Foams Anthony Chieco, Douglas J Durian Quasi 2-dimensional dry foams are made of polyhedral bubbles squashed between two parallel plates that are separated by thin films (TFs) as well as surface Plateau borders (SPBs) along the two plates. Bubbles coarsen because gas diffuses through their TFs and SPBs; gas diffuses more slowly through the SPBs which inflate in size as the liquid content of the foam increases and this slows coarsening in wetter foams. A generalized coarsening equation exists for quasi-2d dry foams with varying liquid content and it predicts average and individual bubble coarsening behavior [Chieco et al, arXiv:2010.06664]. Recently a prediction for the coarsening behavior for “wet” foams where bubbles are unjammed nearly touching circles with only liquid bridges separating them was developed. We flood foaming solution into a sample cell whose width is smaller than the capillary length of the solution so only liquid bridges separate bubbles and compare the coarsening of the bubbles to the expectation. Coarsening induced rearrangements are also studied in the wet systems. We present preliminary results on identifying the locations of rearrangements and explore using softness and machine learning to predict where/when they occur. |
Wednesday, March 17, 2021 4:36PM - 4:48PM Live |
P05.00009: Hydrodynamic fluctuations melt crystals. Marine LE BLAY, Denis Bartolo Consider an elastic lattice and drive it with a homogeneous fluid flow. At first sight this problem might sound trivial: isn’t the crystal merely advected by the flow? In this talk I will show that this seemingly simple question reveals a dramatic role of hydrodynamic interactions in confined liquids. Using microfluidic experiment, we demonstrate how hydrodynamic interactions causes the melting of elastic crystaline emulsions even at zero temperature. Unlike in equilibriium, we show that flow-induced melting of soft crystals does not obey the KTHNY scenario. Instead, melting is a one step process taking the form of a 1st order nonequilibrium transition where macroscopic crystals generically coexist with an isotropic liquids phase. |
Wednesday, March 17, 2021 4:48PM - 5:00PM On Demand |
P05.00010: Stratification in micellar foam films as a probe for intermicellar interactions Chrystian Ochoa, Shang Gao, Samanvaya Srivastava, Vivek Sharma Sodium Naphthenate (NaN) found in crude oils can act as a surfactant and influence the stability, lifetime, and rheology of petroleum foams and emulsions. Here, we show that foam films formed by aqueous micellar solutions of NaN exhibit step-wise thinning or stratification, due to the influence of non-DLVO forces, including supramolecular oscillatory structural forces. We utilize Interferometry, Digital Imaging, Optical Microscopy protocols, previously developed by our group, to investigate the drainage and stratification in micellar foam films (h < 100 nm) with high spatial (thickness ~ 1 nm, in-plane < 1 micron) and temporal resolution (time < 1 ms). We determine how the NaN concentration influences the nanoscopic topography, stratification kinetics, and step size of foam films, and contrast the results with behavior observed with stratifying foams made with sodium dodecyl sulfate (SDS) solutions. We span a relatively wide concentration range, such that micelle shape and size vary, as is revealed by complementary small angle X-ray scattering experiments. |
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