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 J24: Thin FilmsLive
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Sponsoring Units: DFD Chair: Vivek Sharma, University of Illinois at Chicago |
Tuesday, March 16, 2021 3:00PM - 3:12PM Live |
J24.00001: Viscous and Viscoelastic fingering Fahed Albreiki, Alexander Kubinski, Prerana Rathore, Andrew Rasmussen, Vivek Sharma The displacement of more viscous fluid by a lower viscosity fluid in quasi two dimensional flow created in so called Hele Shaw cell is observed to create complex fingering patterns. The viscosity ratio of inner and outer fluid is known to influence the shape and shape evolution of fingers in the case when both fluids are Newtonian. In this contribution, we examine the influence of viscoelasticity on onset and evolution of fingering instabilities, by utilizing model viscoelastic fluids with rate-independent shear viscosity. The analysis of viscoelastic fingering is complemented by a careful evaluation of shear and extensional viscosity as well as Normal stress differences, and their role in determining the outcomes for interfacial~instabilities. |
Tuesday, March 16, 2021 3:12PM - 3:24PM Live |
J24.00002: Viscoelasticity and dynamics of nanoconfined water by atomic force microscopy Peter Hoffmann, Edward Kramkowski, Shah H Khan Our group has conducted extensive measurements of the viscoelastic properties of nanoconfined water in hydrophilic environments using a specialized high-resolution dynamic atomic force microscopy technique. Here we will present an overview of our findings, including the observation of dynamic solidification, the effect of ions on ordering and dynamics, and the recent observation of the compression rate dependence of the effective viscosity. |
Tuesday, March 16, 2021 3:24PM - 3:36PM Live |
J24.00003: Phase Separation of 5CB Liquid Crystal Droplets in the Self-assembling Protein Drops via Evaporative Drying Anusuya Pal, Germano S Iannacchione This presentation aims to show how a series of simple experiments can easily track the complex physical behavior. These experiments present new insights on the self-assembly of bio-colloidal structures in a symmetric drop driven by evaporative drying. Our findings uncover the self-assembly of the globular proteins, bovine serum albumin (BSA), myoglobin (Myo), and lysozyme (Lys), and the phase separation of the nematic liquid crystal, 5CB. The drying evolution and the resulting morphology of these drying drops with and without 5CB droplets are compared through the bright-field and cross-polarizing microscopy. Different regimes of intensity in the presence of 5CB droplets are shown under cross-polarizing configuration, whereas no such variation is observed in its absence in these protein drops. Interestingly, BSA shows a striking result by an umbilical defect in every domain near the periphery of the drop. On the other hand, Myo and Lys exhibit a central dark region in every domain surrounded by a bright region. Finally, under the bright-field configuration, the crack spacing is reduced in the dried Myo and Lys drops with 5CB droplets, whereas no significant difference is found in the dried BSA drop. |
Tuesday, March 16, 2021 3:36PM - 3:48PM Live |
J24.00004: Impact of the wetting length on flexible blade coating Marion Krapez, Anais Gauthier, Hamid Kellay, Jean-Baptiste Boitte, Odile Aubrun, Joanny Jean-Francois, Annie Colin We study a common industrial problem: the spreading of a Newtonian fluid by a deformable blade, which is also paradigmatic of elasto-hydrodynamic interactions. This question has been seen in the light of an elasticity-capillarity analogy, and a parallel with dip coating experiments was proposed to predict the deposited film thickness [1]. To do so, the liquid reservoir was always considered as infinite. Here, we consider the case of a finite reservoir of liquid, emptying as the liquid is spread, a situation corresponding to a large majority of everyday situations, such as the spreading of paint on a wall, or cream on the skin. We evidence the role of a central variable: the wetting length lw, which sets a boundary between the wet and dry parts of the blade. We show that the deposited film thickness depends quadratically with lw. We study this problem experimentally and numerically by integration of the elasto-hydrodynamic equations, and finally propose a scaling law model to explain how lw influences the spreading dynamics. |
Tuesday, March 16, 2021 3:48PM - 4:00PM Live |
J24.00005: Dynamics of Tail Free Liquid Crystals Mitch Powers, Parikshit Guragain, Zhe Li, Robert J Twieg, John Portman, Brett Ellman The overwhelming majority of discotic liquid crystals (DLC's) have rigid cores surrounded by flexible tails that help the molecules self assemble into long columns of molecules separated from each other by a soft buffer of tails. Here we consider a recently discovered set of isomeric tail free compounds, including several which are DLC's despite lacking the tails which are generally considered to be a requirement. We will explore how small structural changes in the molecules are responsible for the formation of a liquid crystalline mesophase through a combination of molecular dynamics simulations and experimental measurements. |
Tuesday, March 16, 2021 4:00PM - 4:12PM Live |
J24.00006: Effect of Molecular Interactions in Thermocapillarity-Driven Flows Martin Maza-Cuello, Laurence Talini, Christian Fretigny The thermocapillarity effect can be used to generate the local thinning of a wetting thin liquid film supported by a solid substrate. This thinning process produces local thicknesses down to a scale of tens of nanometres, at which molecular interactions from the solid-liquid interface become relevant. Within the frame of the lubrication approximation, we show that gravity and Laplace pressures are negligible in these ultra-thin regions, leaving the disjoining pressure as the sole contribution opposing the thermocapillarity stress. This allows us to isolate and characterise the signature of van der Waals interactions in experiments performed with wetting liquids. |
Tuesday, March 16, 2021 4:12PM - 4:24PM Live |
J24.00007: Interfacial slip of liquids along graphene: effects of layering and substrate-induced doping Gus Greenwood, Jin Myung Kim, Qianlu Zheng, Shahriar Nahid, SungWoo Nam, Rosa Espinosa-Marzal Understanding modulation of liquid molecule slippage along graphene surfaces is crucial for many promising applications of two-dimensional materials, such as in sensors, nanofluidic devices and biological systems. In this investigation we use atomic force microscopy (AFM) to directly measure hydrodynamic, solvation, and frictional forces along substrate supported graphene in seven liquids. The results show that the greater slip lengths correlate with the interfacial ordering of the liquid molecules, suggesting that increased ordering in the liquid phase promotes slip while less structured liquids significantly hinder it. This phenomenon is relevant in addition to the commonly referenced wetting behavior and solid-liquid interaction energy. Furthermore, the slip boundary condition of the liquids along the graphene plane is sensitive to the substrate-induced doping of graphene. Because interfacial slip can have prominent consequences on the pressure drop, electrical and diffusive transport through nanochannels and on lubrication, this work can inspire innovation in many applications through the selective doping of graphene surfaces and interfacial order of the contacting liquid. |
Tuesday, March 16, 2021 4:24PM - 4:36PM Live |
J24.00008: Rising and breakup of air in viscous fluids in confined space Ko Okumura The dynamics of liquid-gas interface in confined geometries is fundamentally interesting and relevant for various applications, e.g., related to microfluidics. Recently, we have explored various issues on this, from which we pick up latest three. One is rising dynamics of an air bubble surrounded by viscous liquid in a doubly confined geometry [1]. The system is confined by not only front and back plates of the cell (as in a Hele-Shaw cell) but also the side plates. We establish scaling laws for the rising velocity and drag friction, and further reveal a close relation to an unresolved classic problem regarding viscous fingering. Second is breakup of air induced by a solid disk freely falling in viscous liquid in a Hele-Shaw cell [2]. We discuss a new self-similar regime for the breakup in which the section of air before breakup is not axisymmetric but an ellipse [3]. Third is an unusual case of capillary dynamics, which is not slowing down (thus, different from usual capillary imbibition) but is accelerating. We demonstrate a unified description for the two opposite dynamics [4]. |
Tuesday, March 16, 2021 4:36PM - 4:48PM Live |
J24.00009: Breakup of a thin air film surrounded by viscous liquid: derivation of self-similar solutions Yuka Miyabe, Ko Okumura Recently, we studied a viscous breakup of a fluid sheet and demonstrated an example of self-similar dynamics through agreement between experiment and theory [1]. A simple feature of this example is remaining of a single length scale near the breakup singularity. However, the governing equations have yet to be derived from the first principle. In this study, we successfully derive the self-similar solution from the Navier-Stokes equations, extending a method developed for the axisymmetric breakup [2]. Our case is clearly different from the axisymmetric case, since, as already noted, only a single length scale remains near the critical point. However, both cases are governed by the same principle: the scaling forms are determined in a way to avoid the divergence of dissipation near the critical point. |
Tuesday, March 16, 2021 4:48PM - 5:00PM Live |
J24.00010: A smectic liquid crystal Langmuir film at the air/water interface: boundaries, thermodynamics and dynamics Huda Alwusaydi, Angelo Visco, J. Adin Mann, Elizabeth K Mann Molecularly-thin smectic liquid crystal films at the air/water interface phase separate into regions with different numbers of layers, in analogy with free-standing smectic liquid crystalline films. We explore the boundary between two such regions, using a variety of experimental and numerical methods. We measure the line tension by stretching domains from their equilibrium circular shape and analyzing the free relaxation with a hydrodynamic model. We connect the line tension associated with the boundary to boundary structure and use the association to suggest effective line-active agents, to control the line tension and thus the domain size distribution, shape and dynamics. Such line-active agents, which are not well-understood and have proved difficult to design, are empirically important to dynamic functional domains within cell-membranes. |
Tuesday, March 16, 2021 5:00PM - 5:12PM Live |
J24.00011: Effect of Interfacial Thermal Transport on Water Flow in Graphene Nanochannels Diego Becerra, Jens Honore Walther, Harvey A Zambrano Fluid flow in nanochannels is governed by interfacial phenomena thus thermal transport at solid-liquid interfaces can be a key parameter to design efficient nanodevices. Ultra-low friction to water flow and its exceptional mechanical and thermal properties make graphene a promising material to be used in nanofluidic systems. In a variety of applications, graphene has to be supported on a substrate. Here, we study the role of the underlying substrate on interfacial heat transport in graphene nanochannels. We conduct atomistic simulations of Poiseuille-like flow of water in a nanochannel with walls consisting of monolayer graphene supported on slabs of silica, polyamide and hexagonal boron nitride, respectively. The Joule heating dissipation through the walls is evaluated for different imposed flow rates. Temperature profiles, interfacial energy landscape and transport properties as interfacial viscosity, friction coefficient and water ordering are computed to gain insight into the effect of interfacial heat transport on nanoconfined flow. Density of states (DOS) across the graphene are measured to analyze the influence of the underlying substrates on the phonon thermal transport through the walls. |
Tuesday, March 16, 2021 5:12PM - 5:24PM Live |
J24.00012: Super-Resolution Optical Imaging of Depletion Layer Dynamics Anisha Shakya, Seong Jun Park, John King The dynamics of complex fluids flowing across solid surfaces remains an outstanding problem in fluid mechanics that is relevant for fields including nanofluidics and lubrications. The formation of depletion layers at the boundary has significant implications for the flow of the bulk fluid. However, the inherently small length scales associated with the interfacial physics has traditionally inhibited direct imaging. We developed a novel adaptation of super-resolution microscopy based on stimulated emission depletion (STED) to provide a real-space measurement of depletion layer composition and dynamics of a polyelectrolyte solution under flow with spatial resolution on the order of 50 nm. The composition and dimension of depletion layers formed from poly(styrene sulfonate) at a non-adsorbing wall are measured both at equilibrium and under flow. We observe a concentration profile consistent with entropically driven depletion of the polymer from the interface. Furthermore, under Poiseuille flow at low to intermediate shear rates, we observe depletion layer narrowing coupled with a change in the composition of the depletion layer to nearly pure solvent. |
Tuesday, March 16, 2021 5:24PM - 5:36PM On Demand |
J24.00013: Drainage of protein foams and foam films Lena Hassan, Chenxian Xu, Vivek Sharma Many food,cosmetic and pharmaceutical foams contain proteins that influence both the interfacial and bulk properties of formulations. In this study, we characterize the drainage of protein-based foams as well as single foam films, and contrast their behavior with micellar foams formed with small molecular surfactants above the critical micelle concentration. Micellar foam films undergo drainage via stratification manifested as step-wise thinning in the plots of average film thickness over time. Stratification in micellar foam films is accompanied by formation of coexisting thick-thin regions visualized in reflected light microscopy as exhibiting distinct grey regions as intensity is correlated with thin film interference. We critically examine the drainage of protein foam films to determine how and when stratification can be observed, and evaluate the connection between drainage of single foam films and bulk foams. |
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