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 M06: Wetting and Adhesion of Soft Materials: Dynamics and Instability IILive
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Sponsoring Units: DSOFT GSNP DPOLY Chair: Etienne Barthel, ESPCI Paris Room: 06 |
Wednesday, March 17, 2021 11:30AM - 11:42AM Live |
M06.00001: Direct force measurement of microscopic droplets pulled along soft surfaces Hamza Khattak, Kari Dalnoki-Veress Recently, there has been growing interest in understanding the interactions of liquid droplets with soft materials. In these systems, forces exerted by a droplet can deform the material it contacts. This property leads to a plethora of unique physical phenomena with applications in fields ranging from water collection to surface sensing. We explore droplet dynamics on soft materials using a micropipette-based technique to simultaneously image, and measure the forces on, a microscopic droplet dragged along a soft interface. By changing the thickness of the soft material, we can control the compliance of the soft material independent of surface chemistry. We model the dynamics of the droplet-substrate interaction and expect dissipation to scale with the size of the capillary deformation. We find agreement between our model and experimental results. |
Wednesday, March 17, 2021 11:42AM - 11:54AM Live |
M06.00002: Do soft solids have strain-dependent surface tension? Nicolas Bain, Robert Style, Eric R Dufresne Xu et al. observed (Nat. Commun. 2017) that the opening angle below a wetting ridge increased with the far-field stretch of the substrate. Using a Neumann triangle, this was interpreted to correspond to an increase in the surface tension with strain. Masurel et al. (Phys. Rev. Let. 2019) argued that the coupling between nonlinear bulk elasticity and the geometric singularity at the tip of the wetting ridge suffice to explain the experiments of Xu et al, without invoking the Shuttleworth effect. Here, we describe new experiments investigating possible strain-dependence of the surface tension of a soft solid, in the absence of potentially confounding geometric singularities. |
Wednesday, March 17, 2021 11:54AM - 12:06PM Live |
M06.00003: Contact drawing of core-shell polymer fibers using an aqueous two-phase system SWOMITRA PALIT, John Frampton, Laurent Kreplak Core-shell polymer fibers, prepared primarily through electrospinning-based approaches, have numerous applications, including spun-bonded nonwovens, optics, electronics, as well as self-healing composites, drug delivery, drug release, tissue engineering, and sensors. Our study explores the contact drawing technique and a special class of water-in-water mixtures known as aqueous two-phase systems (ATPSs) to produce core-shell fibers. This approach can be precisely tuned by immersing the end of a microneedle into the ATPS and then retracting it at a defined speed. We investigate core-shell fibers' formation over a wide range of polymer concentrations and molecular weights in the two phases. We also monitor fiber diameter by varying the retracting speed while keeping the final fiber length constant. Fibers prepared in this method are found to have fine dimensional control, continuous fabrication, low production cost and sustainability. |
Wednesday, March 17, 2021 12:06PM - 12:18PM Live |
M06.00004: Multiple drops interacting on swelling fibers Pierre Van de Velde, Camille Duprat, Suzie Protière The Plateau-Rayleigh instability has been extensively described over the last centuries. When a fiber is coated with a thin liquid film, this film can destabilize into multiple droplets. Many fibers such as cellulose, wood or polymer fibers may swell when interacting with a favorable solvent. In this talk, I will show how the Plateau-Rayleigh instability can be affected by the swelling of the fiber. Generally, the curvature of a fiber prevents the total spreading of a drop even if the fluid is fully wetting the fiber. On a swelling fiber, a drop locally penetrates and swells the fiber thus moving further through the polymer network. If two drops are placed close enough to each other on the same fiber, they may interact via the swollen polymer network leading to different spontaneous movements. The drops may drift apart or in some cases attract each other or even coalesce in a counterintuitive manner. In this talk, by making use of our previous work on the absorption of a single drop on a fiber, we attempt to rationalize the dynamics of two or more interacting droplets on a fiber through controlled experiments and simple models. |
Wednesday, March 17, 2021 12:18PM - 12:30PM Live |
M06.00005: Fluid separation and network deformation in wetting of soft and swollen elastomers Zhuoyun Cai, Artem Skabeev, Svetlana Morozova, Jonathan Pham When a water drop is deposited on a soft substrate, the surface tension of water drives an out-of-plane deformation of the substrate; this is commonly known as soft wetting. However, a very soft, crosslinked elastomer often contains a fluid (i.e. solvent) and can be considered a swollen network. During wetting, solvent may separate from network near the contact line to minimize the elastic energy of the substrate deformation. Although phase separation near contact lines has been considered, the amount of solvent separation and network deformation in the wetting ridge is not well understood, and the conditions for phase separation are unclear. We use confocal microscopy to visualize the crosslinked polymer and solvent separately at the wetting ridge. By controlling the degrees of crosslinking and swelling, we investigate how both control the solvent leeching and the network pull-up. With increasing swelling, the solvent separation increases while the network pull-up height decreases, demonstrating a synergy between network deformation and solvent separation. Our results reveal that a swelling fluid, commonly found inside soft networks or slippery surfaces, can play a critical role at the tip of a wetting ridge |
Wednesday, March 17, 2021 12:30PM - 12:42PM Live |
M06.00006: Contact Angle Hysteresis from a thin film suspended on a liquid surface Nuoya Zhou, Deepak Kumar, Benjamin Davidovitch, Narayanan Menon
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Wednesday, March 17, 2021 12:42PM - 12:54PM Live |
M06.00007: Unraveling stability of a floating liquid marble and its collapse patterns Sneha Ravi Apoorva, Sameer Dalvi Liquid marbles (LMs) are droplets of liquid usually enwrapped by hydrophobic particles. Our aim was to analyze collapse dynamics of floating LMs, stability and resulting collapse patterns. PTFE LMs were prepared by rolling a drop at a fixed angle and dynamics of the floating LM collapse was recorded. These LMs showed distinct collapse patterns and times by varying both the core liquid and the liquid substrate. Densely packed petal shaped patterns were obtained in the case of no surface tension gradient between those of core liquid of LM and supporting liquid substrate. On the other hand, porous and diffuse patterns were obtained in the case of surface tension gradient. Aqueous solutions of methylene blue visualized the opening of dipped LM and led us to preparation of robust LMs which remained stable upto 6 hours after which they underwent buckling. Regime of collapse was divided into- petal, porous and buckled LM. Effective surface tension(γeff) was directly related to the stability of floating LM and estimating capillary forces(γint) gave us clues about the nature of interaction between both particle-particle and particle-liquid. Further, changing the temperature of the liquid substrate changed stability of LM without using any temperature responsive coating material. |
Wednesday, March 17, 2021 12:54PM - 1:06PM Live |
M06.00008: Curvature-dependent Contact Angles Chen Ma, Chao Chen, Cunjing Lv, Quanshui Zheng Recent studies showed that the contact angles of fluids on the carbon nanotubes depend on the nanotubes' curvature. However, the trends of the curvature effect were contradictory, and underline physics has not been fully revealed. This work presents for the first time a molecular perspective of curvature effect on the contact angles. We develop an analytic theory without fitting parameters based on the Young-Dupré equation to provide a fundamental understanding of the intrinsic nature of the curvature effect, which is validated quantitatively by molecular dynamics simulations on water droplets in contact with carbon nanotubes. We find that the contact angle decreases on a concaved substrate and vice versa. A curved hydrophilic surface demonstrates a more significant influence. Additionally, the curvature effect's length scale is governed by the atomic interaction range between liquid and solid. We anticipate that the new understanding of the nanoscale wetting gives new insight into the design of nano-flow systems and the stable superhydrophobic surfaces. |
Wednesday, March 17, 2021 1:06PM - 1:18PM Live |
M06.00009: Interfacial tension and wettability of water solution on hydrophilic and hydrophobic surfaces Meng Shen It is well known that the surface tension of water is reduced by surfactants. For interfacial tension, however, the spatial arrangement of surfactants is affected by the opposing solid or liquid against water and the charge and activity of surfactants. Here, using atomistic and coarse-grained molecular dynamics simulations, we study the interfacial tension and wettability of water containing amphiphilic molecules, charged surfactants and active surfactants against hydrophilic and hydrophobic surfaces. The research will shed light on the adhesion of droplets, such as virus-containing aerosol, on different types of surfaces. |
Wednesday, March 17, 2021 1:18PM - 1:30PM Live |
M06.00010: Discontinuous curvature in a thin-film profile near a three-phase contact line Deepak Kumar, Narayanan Menon, Benjamin Davidovitch The contact line at a solid-liquid-vapor interface is a region of localized forces. However, if the solid phase is thick and stiff, the consequent singularity in the otherwise smooth interfacial surfaces is barely noticeable. In this work, we address the nature of such a singular behavior when the solid phase is very stiff but also highly bendable. We study a system consisting of a thin polymer film partly floating on water with one end lifted up in the air, whose one-dimensional nature simplifies considerably the theory as well as collecting and analyzing high-quality data. Observing the contact line at capillary length scale (millimetres), over which the solid elasticity has a negligible effect, we show that the slope jumps at the three-phase contact line, and the shape is accurately described by the classical Young-Laplace equation. When observing the contact line over the bendo-capillary scale (~10-100 micrometres in our experiment), where bending energy is comparable to surface energy, we find that the discontinuity in the slope of the polymer film is regularised and the profile looks smooth. However, we find that even at this bendo-capillary scale, a higher-order discontinuity exists in the derivative of the curvature. |
Wednesday, March 17, 2021 1:30PM - 1:42PM Not Participating |
M06.00011: Non-Sticking Polymeric Surfaces: Dynamics of Nano Structured Fluorinated Polymeric Thin Films Dvora Perahia, Manjula Senanayake, Sunil K Sinha The adhesion characteristics of interfaces of structured co-polymers is essential for many coating applications. These interfaces consist of domains of all segments, each with its unique characteristic adhesion, where the overall interfacial behavior depends on the dynamics at the boundary. While in simple liquids interfacial dynamic is well captured by capillary waves, increasing complexity of the polymers result in interfacial dynamics that is affected by the structure of the macromolecules in the film. Here we report Xray Photon Corelation Spectroscopy (XPCS) study of the interfacial dynamics of thin liquid films of semi-fluorinated polymer melts that consist of alternating fluorinated and protonated segments. The interface of these polymers exhibit nano-structured H and F domains, whose size depend on the segment length. We find that despite the fact that in average fluorinated segments reduce surface tension, the interfacial dynamics differs from that of capillary waves, where increasing the fraction of fluorinated segments reduces the fluctuations. |
Wednesday, March 17, 2021 1:42PM - 1:54PM Live |
M06.00012: Anisotropic wetting on simple, flat surfaces Katrina Smith-Mannschott, Qin Xu, Nicolas Bain, Stefanie Heyden, Eric R Dufresne, Robert Style Anisotropic wetting in nature and in the laboratory is typically associated with complicated chemical or topographical patterning. We show that, surprisingly, even soft, flat surfaces exhibit anisotropic wetting - both in statics and dynamics. Droplets sliding on a soft substrate with 23% stretch move approximately 70% faster parallel to the stretch direction than perpendicular. A stretched substrate with static droplets reveal increasing ellipticity with larger stretches. We connect both of these phenomena to the deformations of the substrate by the droplet along its contact line, the shape of which is strongly dependent on the applied stretch. Here we examine and analyze this deformation with a combination of confocal microscopy and optical profilometry in order to understand the factors that determine the anisotropic wetting behavior and to discuss the cause of the strong stretch-dependence of the anisotropic deformations. |
Wednesday, March 17, 2021 1:54PM - 2:06PM Live |
M06.00013: A Computational Mesoscale Study of the Adhesion of Nanocarriers to Endothelial Cells Saeed Akbari, Shaghayegh Khani, Joao M Maia Herein, we present a computational analysis of nanocarrier adhesion to and absorption by endothelial cells through Dissipative Particle Dynamics simulations. Two sizes of spherical nanocarrier each in bare and ligand functionalized format are examined in terms of most of the system parameters that influence the binding process. A binding analysis is performed upon immersion of the individual nanocarrier in the system with a substrate, glycocalyx layer, receptors and water. The effect of ligand composition and nanocarrier size provides additional understanding of the binding kinetics. Furthermore, the effect of glycocalyx resistance and receptor rigidity on binding efficiency are characterized in detail. |
Wednesday, March 17, 2021 2:06PM - 2:18PM On Demand |
M06.00014: Surface textures suppress visco-elastic braking on soft substrates Martin Coux, John M Kolinski A gravity driven droplet will rapidly flow down an inclined substrate, resisted only by stresses inside the liquid. If the substrate is compliant, with an elastic modulus G < 100 kPa, the droplet will markedly slow as a consequence of viscoelastic braking. This phenomenon arises due to deformations of the solid at the moving contact line, enhancing dissipation in the solid phase. Here, we pattern compliant surfaces with textures and probe their interaction with droplets. We show that the superhydrophobic Cassie state, where a droplet is supported atop air-immersed textures, is preserved on soft textured substrates. Confocal microscopy reveals that every texture in contact with the liquid is deformed by capillary stresses. Surprisingly, droplet velocities down inclined soft or hard textured substrates are indistinguishable; the textures thus suppress visco-elastic braking despite substantial fluid-solid contact. High-speed microscopy shows that contact line velocities atop the pillars vastly exceed those associated with visco-elastic braking. This velocity regime involves less deformation, thus less dissipation, in the solid phase. Such rapid motions are only possible because the textures introduce a new scale and contact line geometry. |
Wednesday, March 17, 2021 2:18PM - 2:30PM On Demand |
M06.00015: Wetting Driven Globule-to-Brush Transition of Polymer-grafted Surfaces Sai Etha, Parth Rakesh Desai, Harnoor Sachar, Siddhartha Das Studying the behavior of liquid drops on surfaces of various complexities is critical in the design and fabrication of a wide range of surfaces. A proper understanding of the surface wettability can be employed in various energy and biomedical applications as well as applications such as enhanced oil-water separation, anti-biofouling etc. We employ Molecular Dynamics (MD) simulations to probe the spreading and imbibition of a liquid drop on a surface grafted by polymer molecules and observe their transition from an initially collapsed globule-like state, to a brush-like state upon wetting. We hypothesize that the drop spreading behavior is dictated by a balance between the inertial pressure and the viscoelastic dissipation associated with the polymer layer undergoing this transition. Our MD results indicate that the rheology of the polymer layer, behaving like a viscoelastic solid, can be described by a power-law index of n=2/3, ensuring that the scaling calculations recover the simulation predictions. We also observe that the dynamics of the polymer layer swelling depend on the grafting density and is faster for sparser grafting, and we recover the equilibrium polymer brush height scaling with grafting density, thus confirming a brush-like configuration of the polymer layer. |
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