Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session B54: Soft Interface Mechanics IIFocus Prize/Award
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Sponsoring Units: GSOFT DBIO DPOLY Chair: Qin Xu, ETH - Zurich Room: LACC 514 |
Monday, March 5, 2018 11:15AM - 11:27AM |
B54.00001: Elastocapillary Wetting: Square Holes and Square Droplets Rafael Schulman, John Niven, Michiel Hack, Christian DiMaria, Kari Dalnoki-Veress We present experiments examining wetting and dewetting of liquids capped by thin elastomeric films. In the dewetting experiments, increasing the isotropic tension of the capping elastomeric layer leads to flatter dewetting rims, and consequently, a slower dewetting speed. This result is consistent with an analogue experiment wherein partially wetting droplets are capped by thin elastic films, and increasing the tension decreases the contact angle. We show that using thin elastic films to cap a liquid presents a new avenue for patterning. By suitable choices of the elastic boundary conditions, holes and droplets can assume elliptical and square morphologies. |
Monday, March 5, 2018 11:27AM - 11:39AM |
B54.00002: Mechanics of Shape Shifting Droplets Ireth Garcia-Aguilar, Piermarco Fonda, Luca Giomi, Eli Sloutskin Liquid droplets of oil emulsions in water have been observed to spontaneously deform into polyhedral shapes as the system is cooled down. Spherical droplets undergo faceting and other shape transitions at temperatures where the interface monolayer freezes into a hexagonal crystal while the bulk oil and water remain liquid. While a planar interface could be tiled perfectly by a hexagonal lattice, a sphere is topologically constrained to accommodate defects, which induce deforming local stresses. We seek to understand the mechanism driving the volume-conserving deformations by modelling the droplets as 2D elastic surfaces. By looking at the interplay of the elastic energy, surface tension and buoyancy, we have been able to gain insight into the temperature-dependent behaviour of the droplets. Our analysis has led to the study of the size scaling properties of defect-induced stress and its coupling to the curvature of the surface. We have found this coupling to be key in explaining the mechanics behind the shape transformations. |
Monday, March 5, 2018 11:39AM - 11:51AM |
B54.00003: Enhanced dip-coating on a soft substrate Vincent Bertin, Manon Marchand, Christophe Poulard, Elie Raphael, Frederic Restagno, Emmanuelle Rio, Thomas Salez, François Boulogne
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Monday, March 5, 2018 11:51AM - 12:03PM |
B54.00004: Taking the plunge into forced wetting with unprecedented precision Mengfei He, Sidney Nagel When a flat solid substrate is swiftly thrust across the interface between two fluids (e.g., water and air), it entrains a thin film of the trailing fluid attached to its surface. The onset of this ‘forced wetting’ phenomenon has been extensively studied in terms of a two-dimensional geometry in which no flows occur transverse to the direction of motion of the solid surface. Contrary to this assumption, we have discovered that in steady state the fluid interface develops a characteristic three-dimensional structure: there are multiple thin and thick regions of the fluid film alternating in the transverse direction. This structure occurs robustly both in wetting (solid plunged into the liquid) and dewetting (solid removed from liquid). This shows that the flow behind the contact line is not invariant in the transverse direction suggesting the existence of a new instability. Using a new interference technique, we measure the thickness of the thick and thin regions as a function of substrate velocity and fluid viscosity. We compare these results with the Landau-Levich-Derjaguin model generalized to incorporate viscous effects from both fluids. |
Monday, March 5, 2018 12:03PM - 12:15PM |
B54.00005: X-ray microscopic observations of Cassie-Baxter wetting behaviors Su Jin Lim, Donggyu Kim, Yeseul Kim, Hee Kyeong Park, Suyeon Jeong, Changhyun Pang, Seunghwa Ryu, Byung Mook Weon Cassie-Baxter wetting is prevailing in nature, for instance on lotus leaves and the body of the water strider, as well as on hydrophobic micropatterned surfaces, enabling to superhydrophobicity. Cassie-Baxter wetting is widely known to exhibit a flat bottom of a droplet on the top of the micropatterned surface. Occasionally a droplet has been found to be partially impaled into micropatterns and its bottom looks curved as observed with interference techniques, confocal microscopy, X-ray microscopy, and simulations. Here we clearly observe Cassie-Baxter wetting behaviors with high-resolution high-speed X-ray microscopy. We demonstrate that occurrence of flat or curved bottoms of a droplet is dependent on droplet volume, initial wetting, and micropattern geometry. Consequently, new interpretation for Cassie-Baxter wetting is suggested with respect to minimization of surface free energy. |
Monday, March 5, 2018 12:15PM - 12:27PM |
B54.00006: Cassie-Baxter State Can Explain the Impaled State Donggyu Kim, Su Jin Lim, Yeseul Kim, Byung Mook Weon, Seunghwa Ryu Cassie-Baxter state refers to the wetting state where the droplet is on the rough surface underneath which small air pockets lie, and is responsible for the super-hydrophobicity. While the classical Cassie-Baxter model assumes the flat bottom surface of the droplet, recent experiments show that the droplet on the patterned surface may have the curved bottom surface and stay as the impaled state, which remains not well understood. In this study, we suggest a new theory that can explain the impaled state by modelling the droplet with two spherical caps, sharing the basal surface of the upper one. We conduct numerical free energy analysis to show that the curvature of the bottom surface of the droplet is essential to stabilize the droplet in impaled state, especially when the size of the droplet is comparable to the characteristic length scale of the substrate pattern. Our study offer a more precise description of the droplet in Cassie-Baxter state and can be used to analyze the wetting transition between Cassie-Baxter and the Wenzel state. |
Monday, March 5, 2018 12:27PM - 12:39PM |
B54.00007: Magnetorheology for Reduction of Blood Viscosity, Turbulence, and Atherosclerosis Rongjia Tao, Michael Autieri, Kazi Tawhid-Al-Islam Despite nutritional modification and lipid reducing medications, atherosclerotic vascular syndromes account for 50% of all mortality in US. It is well known that disturbed blood flow hemodynamics make different regions of the vasculature interface vulnerable to development of atherosclerotic plaque, and that growing plaque generates more biomechanical force to disturb blood flow. Currently, there is no modality which targets disturbed blood flow to reduce growth atherosclerotic plaque. Here we report our finding with magnetorheology: application of a strong magnetic field to blood along its flow direction, red blood cells are polarized in the magnetic field and aggregated into short chains along the flow direction. The blood viscosity becomes anisotropic: Along the flow direction the viscosity is significantly reduced, but in the directions perpendicular to the flow the viscosity is considerably increased. THe disturbed blood flow is thus suppressed, becomes laminar, and the blood circulation is greatly improved. Our recent tests with mice show that this technology can effective prevent development of atherosclerotic plaque on the vasculature interface. The physics of hemodynamics leads us to find a solution to prevent heart attacks.. |
Monday, March 5, 2018 12:39PM - 12:51PM |
B54.00008: Surface Stress and Surface Tension in Polymeric Networks Heyi Liang, Zhen Cao, Zilu Wang, Andrey Dobrynin Understanding of how surface properties could change upon deformation is important for controlling adhesion, friction and lubrication of soft polymeric materials. We use a combination of the theoretical calculations and coarse-grained molecular dynamics simulations to study surface stress dependence on deformation in films made of soft and rigid polymeric networks. Simulations show that films of polymeric networks could demonstrate surface properties of both polymer melts and elastic solids depending on their deformation. In particular, at small film deformations the film surface stress Υ is equal to the surface tension obtained at zero film strains, γ0, and surface properties of networks are similar to those of polymer melts. The surface stress begins to show a strain dependence when the film deformation ratio λ approaches its maximum possible value λmax corresponding to fully stretched network strands without bond deformations. In the entire film deformation range the normalized surface stress Υ(λ)/γ0 is a universal function of the ratio λ/λmax. Simulation data for large film deformations point out that the significant increase in the surface stress is due to the onset of the bond deformation. In this deformation regime network films behave as elastic solids. |
Monday, March 5, 2018 12:51PM - 1:03PM |
B54.00009: On the delamination of thin elastic sheet from soft adhesive substrate Oz Oshri, Ya Liu, Kieran Patrick Fitzmaurice, Anna Balazs Thin elastic sheet that is resting on soft adhesive substrate and uniaxially compressed from the boundaries forms a delamination blister when the adhesion energy, wad, is small enough. In the present study we derive an approximate solution to the problem, yet nonlinear, and compare it to the known solution of a blister on a rigid substrate. While the latter presents discontinuity at the threshold of delamination and depends solely on the elasto-capillary length-scale, Ιec=(B/wad)1/2, where B is the bending modulus, the former is continuous and depends, in addition to Ιec, on the capillary length-scale, Ιc=(wad/K)1/2, where K is the substrate stiffness. Nevertheless, the two solutions converge for large confinement up to a narrow boundary layer that forms around the take-off point. Across this layer the bending moment rapidly decays to zero. In addition, we utilize our solution to derive the details of the flat-to-blister and the wrinkles-to-blister instabilities and to construct the “phase-diagram” of the system. |
Monday, March 5, 2018 1:03PM - 1:15PM |
B54.00010: Self-Assembly by deionization, coacervation, and epitaxy Rodrigo Guerra, Paul Chaikin Surface charging and ionic conductance are ubiquitous properties of colloidal suspensions that also profoundly affect their stability and phase behavior. Rigorous deionization induces long-range electrostatic forces that can drive colloidal crystallization, and small changes in salinity can drive large changes in the assembly of oppositely charged polyelectrolytes. Here we demonstrate a new technique to control the salinity of colloids in-situ, and show how it may be combined with the physics of polyelectrolyte coacervation and epitaxial templating to produce self-assembled crystals of oppositely charged colloidal particles. |
Monday, March 5, 2018 1:15PM - 1:27PM |
B54.00011: Investigating the role of geometry on the adhesive strength of mussel inspired structures Marcela Areyano, Luke Gockowski, Megan Valentine This study investigates the mechanical origins of the adhesive strength of marine mussel plaque/thread structures via synthetic mimics. We aim to develop a deeper, predictive understanding of how the geometry and material properties of the plaque impact structural deformation, interfacial energy dissipation, and ultimately, adhesion. Using custom-designed 3D printed molds, we can quickly manufacture and test a wide range of bio-inspired shapes and geometries. Experimentally, we measure the pull off forces as a function of geometric parameters at a range of loading angles, while the resulting structural deformation and the different failure modes are observed, thereby providing insight into how stresses are dissipated and concentrated throughout the structure. We anticipate that these studies will lead to an improved understanding of how the geometric design of soft structures can be used to control their adhesion, enabling the development of bioinspired adhesives with superior capabilities for applications in biomedical, aerospace, and structural engineering. |
Monday, March 5, 2018 1:27PM - 1:39PM |
B54.00012: Interstitial Water Enhances Sliding Friction Adrian Defante, Alex Nyarko, Sukhmanjot Kaur, Tarak Burai, Ali Dhinojwala Motivated by the need to understand the role of interfacial processes like adhesion and friction between surfaces of different interfacial energies, we probe such an interface in this study. Here, we create surfaces having a range of surface energies and bring them in contact with a hydrophobic lens. Our results show that adhesion energy decreases monotonically with an increase in interfacial energy, whereas sliding friction maximizes when the interfacial energy is moderately hydrophobic, within the contact angle range of 60° - 70°. These results indicate that coefficient of friction measured underwater is related to adhesion hysteresis depending on the wetness of the contact area. Consequently, surface sensitive sum frequency generation spectroscopy is used to probe the interface during static contact and dynamic sliding to understand the nature of confined water. Although interstitial water is used to reduce the amount of friction between two surfaces, the spectroscopy results show that under certain cases of contact, the presence of water increases friction. The impact of our results provides guidance for tuning interfacial energy using a simple, scalable, and inexpensive method to mass-produce a variety of adhesive materials for underwater applications. |
Monday, March 5, 2018 1:39PM - 2:15PM |
B54.00013: 2018 Maria Goeppert Mayer Award Talk: Surface tension is weird in confluent biological tissues Invited Speaker: M Lisa Manning Many tissues in your body are composed of tightly packed, or confluent, cells. The mechanical properties and dynamical behavior of these "materials" help govern important processes such as embryonic development, wound healing, and cancer progression. Happily, models for these tissues also exhibit rich and unexpected physics. In this talk, I will focus on “tissue surface tension” which describes interfaces between two tissue types and may help govern biologically relevant patterning such as cell sorting and tissue compartmentalization. We study the properties of a simple model for confluent tissues with “heterotypic” contacts, where unlike cells alter the mechanics of their shared interface. When probed by global mechanical measurements, interfaces between two tissue types behave just as predicted from equilibrium statistical mechanics, but the interfaces are orders of magnitude sharper than expected from standard capillary wave arguments. We show that this sharpness is a special feature generated by the topological nature of the cell-cell interactions. This work has interesting implications for interactions between jamming and tissue surface tension (e.g. “biological elastocapillarity”) and boundaries in other systems, like bird flocks, that may have topological interactions. |
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