Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session D31: Wetting and Adhesion of Soft Materials: Dynamics and Instability IFocus
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Sponsoring Units: DSOFT GSNP DPOLY Chair: Julien Chopin, ESPCI Paris Room: 503 |
Monday, March 2, 2020 2:30PM - 3:06PM |
D31.00001: From dewetting to adhesion rupture - moving lines in dissipative, heterogeneous systems Invited Speaker: Etienne Barthel Thirty five years ago, two theories for the pinning of elastic lines by heterogeneities have appeared almost simultaneously (Joanny & de Gennes, J. Chem. Phys. 81 (1984) 552; Rice, J. Appl. Mech 52 (1985) 571). Starting from these results, a large number of models and simulations have greatly advanced our understanding of complex line phenomena, and especially wetting hysteresis and fracture toughness of heterogeneous materials. However, these theories provide quasistatic pictures and they do not tell us much about what happens beyond the depinning treshold in the rather ubiquitous case where the response of the material itself is dissipative (e.g. viscous liquids or viscoelastic solids). In fact, even for homogeneous systems, evaluating the dissipation is still often a problematic question and the most simple cases - dewetting newtonian liquid or adhesion rupture for a linear viscoelastic solid - are far from being completely understood, especially when confrontion with experimental results is intended... Here we consider the dynamics of a front in a dissipative material moving on a heterogeneous surface at finite velocity. Based on recent numerical results for periodic substrates, we will first show how heterogeneities renormalize the dynamics of newtonian fluids near the dynamic wetting transition and actually obliterate some of the details of the wetting problem. We will then discuss the generalization to the case of dissipative soft solids. |
Monday, March 2, 2020 3:06PM - 3:18PM |
D31.00002: Adhesion in Capillary Assembled Origami Structures Timothy J Twohig, Andrew Croll Adhesion plays an important and often overlooked role in capillary assembly driven thin-film origami systems. Strong adhesion to a substrate can completely inhibit capillary forces from assembling a structure, while weak film-film adhesion means a structure may not be stable in the assembled configuration. In this work, we experimentally study thin-film/substrate and thin-film/thin-film adhesive interactions in order to explore the interplay between capillary forces, thin-film elasticity, bending, and adhesion. We use elastocapillary scaling models to highlight how the basic underlying physics can provide guidelines for building stable thin-film origami structures. |
Monday, March 2, 2020 3:18PM - 3:30PM |
D31.00003: Morphology of adhesive creases Martin Essink, Anupam Pandey, Stefan Karpitschka, Michiel van Limbeek, Jacco Snoeijer When a soft elastic material is compressed beyond a certain critical strain, the free surface turns unstable and forms a crease. This corresponds to a sharp fold of the surface onto itself, leading to intricate morphologies as observed for growing tissues and swelling gels. Self-adhesion within the folded region is known to affect nucleation and hysteresis, but a detailed description has remained elusive. Here we resolve the geometry and mechanics of adhesive creases, combining numerical simulations, analysis and experimental results — with specific attention to the singular edge of the self-contact. It turns out that adhesive creases exhibit a universal shape that arises from a balance of elastic and surface energies. From this we derive a scaling theory for the intricate bifurcation scenario, explaining the hysteretic nucleation of adhesive creases. |
Monday, March 2, 2020 3:30PM - 3:42PM |
D31.00004: Energy Approach to Understand Contact Mechanics on Rough Surfaces Siddhesh Dalvi, Abhijeet Gujrati, Tevis D.B. Jacobs, Lars Pastewka, Ali N Dhinojwala Understanding the deformation of elastic solids on rough surfaces is crucial for soft-hard contacts at different scales of applications such as biomedical adhesives, tire traction, soft robotics and even micro- or nano-electromechanical devices. It has been experimentally demonstrated that the apparent work of adhesion for a soft material brought in contact with rough surfaces is lower than the intrinsic work of adhesion. During separation, there is energy loss commonly attributed to viscoelastic dissipation, termed as adhesion hysteresis. Here, with |
Monday, March 2, 2020 3:42PM - 3:54PM |
D31.00005: Interfacial tension measurement of reconstructive interfaces Hideaki Yokoyama, Masayuki Saito New fabrication method of polymer brushes, “dynamic polymer brush”, was developed recently. In the system where amphiphilic diblock copolymers are added to hydrophobic elastomer, they avoid the elastomer surface in air, but, upon contact with water, spontaneously segregate to the elastomer/water interface and form highly dense polymer brush to lower the interfacial tension. This system is one of many reconstructive surfaces, which change the interfacial structures upon contact with water and hence direct evaluation of interfacial tension is difficult with conventional contact angle measurement. To measure interfacial tension of reconstructive interface, we developed a novel method using elastomer thin films floating on water. Thin films on water was observed by Brewster imaging and their size change was analyzed using the force balance of surface tensions, interfacial tension and elastic force of thin film. The interfacial tension between water and reconstructive elastomer directly measured by this method drastically decreases down to zero due to the dense PEG brushes appeared at elastomer/water interface. |
Monday, March 2, 2020 3:54PM - 4:06PM |
D31.00006: Capillary instability of soft cylinders: Dynamical selection of nonlinear states Minkush Kansal, Anupam Pandey, Miguel Angel Herrada, Jens G Eggers, Jacco Snoeijer Surface tension plays a key role for phenomena involving liquid interfaces. A prime example is the Rayleigh-Plateau instability, causing a liquid jet to break into droplets in order to minimise the surface energy. Remarkably, a similar capillary instability was observed in soft solids. Here we reveal the intricate morphologies that can be encountered during the capillary collapse of an elastic cylinder, from minimisation of capillary and elastic energy. Subsequently, we show the dynamical selection of the wavelength, which also dictates the final nonlinear state. It is found that near the onset of instability, the shapes resemble a “cylinders-on-a-string” configuration, while as the solid gets softer “beads-on-a-string” are observed — in analogy to the breakup of viscoelastic liquids. Our analysis explains recent experimental and numerical observations, and highlights how surface tension can dictate the mechanics of solids - provided that the solids are sufficiently soft. |
Monday, March 2, 2020 4:06PM - 4:18PM |
D31.00007: How Aqueous Salt Solutions Affect Hydrophobic Surfaces Adele Poynor, Cayton Hornberger, Grace Rohaley, Juliana Sebolt The study of how salty water meets a hydrophobic surface is important because in nature water is rarely pure. In order to study this phenomenon, we need smooth and homogenous surfaces; however, salt solutions can damage our surfaces. We study this damage for a variety of self-assembled monolayers (SAMs) in different aqueous salt solutions, using contact angle measurements, scanning electron microscopy, surface plasmon resonance. |
Monday, March 2, 2020 4:18PM - 4:30PM |
D31.00008: Determination of Interfacial Strain on Single-Layer Graphene Due to Ice Adhesion Subash Kattel, Joseph R Murphy, Samuel Pasco, John Ackerman, Vladimir Alvarado, WIlliam Rice Adhesion between two dissimilar media produces a strain that changes the bond character of both materials at the interface, like ice-material interface. To explore the interfacial adhesion properties of ice, researchers apply an external stress directly to ice while measuring strain until adhesive or cohesive failure. This destructive approach masks the intrinsic forces as well as complicated interfacial physics occurring at the ice-material interface. Here, we use Raman spectroscopy to non-perturbatively and contactlessly measure ice-induced strain. To isolate this interface, we probe the vibrational modes of single-layer graphene (SLG) from 20°C to -30°C with and without ice. Along with the well-known temperature-dependent Raman shift of SLG, a clear, ∼-2 cm-1 change in the 2D-frequency (2650 cm-1) developed upon ice formation. We found that at the same temperature, a decrease in the Raman shift emerged between supercooled water and ice, which corresponds to 0.013% strain in SLG solely due to ice. The localized nature of the Raman probe allows for spatial mapping of the ice-coated SLG surface, enabling precise correlation with surface roughness evaluation and theoretical models. |
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D31.00009: Capillary imbibition in a square tube Tian Yu, Jiajia Zhou, Masao Doi We study the wetting of a capillary with a square cross-section. When a square tube is brought in contact with bulk liquid, the liquid wets the corners of the tube and creates finger-like wetted regions. The wetting of the liquid then takes place with the growth of two parts, the bulk part where the cross-section is entirely filled with the liquid and the finger part where the cross-section of the tube is partially filled. In previous works, the growth of these two parts has been discussed separately. Here we conduct the analysis by explicitly accounting for the coupling of the two parts. We propose coupled equations for liquid imbibition in both parts and show that the lengths both increase in time following Lucas–Washburn’s law, but the coefficients are different from those obtained in the previous analysis that ignored the coupling. |
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