1
|
Jeon H, Chao Y, Karpitschka S. Moving wetting ridges on ultrasoft gels. Phys Rev E 2023; 108:024611. [PMID: 37723757 DOI: 10.1103/physreve.108.024611] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2023] [Accepted: 06/28/2023] [Indexed: 09/20/2023]
Abstract
The surface mechanics of soft solids are important in many natural and technological applications. In this context, static and dynamic wetting of soft polymer gels has emerged as a versatile model system. Recent experimental observations have sparked controversial discussions of the underlying theoretical description, ranging from concentrated elastic forces over strain-dependent solid surface tensions to poroelastic deformations or the capillary extraction of liquid components in the gel. Here we present measurements of the shapes of moving wetting ridges with high spatiotemporal resolution, combining distinct wetting phases (water, FC-70, air) on different ultrasoft PDMS gels (∼100Pa). Comparing our experimental results to the asymptotic behavior of linear viscoelastocapillary theory in the vicinity of the ridge, we separate reliable measurements from potential resolution artifacts. Remarkably, we find that the commonly used elastocapillary scaling fails to collapse the ridge shapes, but, for small normal forces, yields a viable prediction of the dynamic ridge angles. We demonstrate that neither of the debated theoretical models delivers a quantitative description, while the capillary extraction of an oil skirt appears to be the most promising.
Collapse
Affiliation(s)
- Hansol Jeon
- Max Planck Insitute for Dynamics and Self-Orgnization, 37077 Göttingen, Germany
| | - Youchuang Chao
- Max Planck Insitute for Dynamics and Self-Orgnization, 37077 Göttingen, Germany
| | - Stefan Karpitschka
- Max Planck Insitute for Dynamics and Self-Orgnization, 37077 Göttingen, Germany
| |
Collapse
|
2
|
Henkel C, Essink MH, Hoang T, van Zwieten GJ, van Brummelen EH, Thiele U, Snoeijer JH. Soft wetting with (a)symmetric Shuttleworth effect. Proc Math Phys Eng Sci 2022; 478:20220132. [PMID: 35937429 PMCID: PMC9347665 DOI: 10.1098/rspa.2022.0132] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2022] [Accepted: 07/04/2022] [Indexed: 11/12/2022] Open
Abstract
The wetting of soft polymer substrates brings in multiple complexities when compared with the wetting on rigid substrates. The contact angle of the liquid is no longer governed by Young’s Law, but is affected by the substrate’s bulk and surface deformations. On top of that, elastic interfaces exhibit a surface energy that depends on how much they are stretched—a feature known as the Shuttleworth effect (or as surface-elasticity). Here, we present two models through which we explore the wetting of drops in the presence of a strong Shuttleworth effect. The first model is macroscopic in character and consistently accounts for large deformations via a neo-Hookean elasticity. The second model is based on a mesoscopic description of wetting, using a reduced description of the substrate’s elasticity. While the second model is more empirical in terms of the elasticity, it enables a gradient dynamics formulation for soft wetting dynamics. We provide a detailed comparison between the equilibrium states predicted by the two models, from which we deduce robust features of soft wetting in the presence of a strong Shuttleworth effect. Specifically, we show that the (a)symmetry of the Shuttleworth effect between the ‘dry’ and ‘wet’ states governs horizontal deformations in the substrate. Our results are discussed in the light of recent experiments on the wettability of stretched substrates.
Collapse
Affiliation(s)
- C. Henkel
- Institut für Theoretische Physik, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Str. 9, Münster 48149, Germany
| | - M. H. Essink
- Physics of Fluids Group, Faculty of Science and Technology, Mesa+ Institute, University of Twente, Enschede 7500 AE, The Netherlands
| | - T. Hoang
- Physics of Fluids Group, Faculty of Science and Technology, Mesa+ Institute, University of Twente, Enschede 7500 AE, The Netherlands
| | | | - E. H. van Brummelen
- Multiscale Engineering Fluid Dynamics Group, Department of Mechanical Engineering, Eindhoven University of Technology, PO Box 513, Eindhoven 5600 MB, The Netherlands
| | - U. Thiele
- Institut für Theoretische Physik, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Str. 9, Münster 48149, Germany
- Center for Nonlinear Science (CeNoS), Westfälische Wilhelms-Universität Münster, Corrensstr. 2, Münster 48149, Germany
| | - J. H. Snoeijer
- Physics of Fluids Group, Faculty of Science and Technology, Mesa+ Institute, University of Twente, Enschede 7500 AE, The Netherlands
| |
Collapse
|
3
|
Bain N, Jagota A, Smith-Mannschott K, Heyden S, Style RW, Dufresne ER. Surface Tension and the Strain-Dependent Topography of Soft Solids. PHYSICAL REVIEW LETTERS 2021; 127:208001. [PMID: 34860052 DOI: 10.1103/physrevlett.127.208001] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/28/2021] [Revised: 08/23/2021] [Accepted: 09/30/2021] [Indexed: 06/13/2023]
Abstract
When stretched in one direction, most solids shrink in the transverse directions. In soft silicone gels, however, we observe that small-scale topographical features grow upon stretching. A quantitative analysis of the topography shows that this counterintuitive response is nearly linear, allowing us to tackle it through a small-strain analysis. We find that the surprising increase of small-scale topography with stretch is due to a delicate interplay of the bulk and surface responses to strain. Specifically, we find that surface tension changes as the material is deformed. This response is expected on general grounds for solid materials, but challenges the standard description of gel and elastomer surfaces.
Collapse
Affiliation(s)
- Nicolas Bain
- Department of Materials, ETH Zürich, 8093 Zürich, Switzerland
| | - Anand Jagota
- Departments of Bioengineering, and of Chemical and Biomolecular Engineering, Lehigh University, Bethlehem, Pennsylvania 18017, USA
| | | | - Stefanie Heyden
- Department of Materials, ETH Zürich, 8093 Zürich, Switzerland
| | - Robert W Style
- Department of Materials, ETH Zürich, 8093 Zürich, Switzerland
| | - Eric R Dufresne
- Department of Materials, ETH Zürich, 8093 Zürich, Switzerland
| |
Collapse
|
4
|
Smith-Mannschott K, Xu Q, Heyden S, Bain N, Snoeijer JH, Dufresne ER, Style RW. Droplets Sit and Slide Anisotropically on Soft, Stretched Substrates. PHYSICAL REVIEW LETTERS 2021; 126:158004. [PMID: 33929254 DOI: 10.1103/physrevlett.126.158004] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/04/2020] [Revised: 01/21/2021] [Accepted: 03/03/2021] [Indexed: 06/12/2023]
Abstract
Anisotropically wetting substrates enable useful control of droplet behavior across a range of applications. Usually, these involve chemically or physically patterning the substrate surface, or applying gradients in properties like temperature or electrical field. Here, we show that a flat, stretched, uniform soft substrate also exhibits asymmetric wetting, both in terms of how droplets slide and in their static shape. Droplet dynamics are strongly affected by stretch: glycerol droplets on silicone substrates with a 23% stretch slide 67% faster in the direction parallel to the applied stretch than in the perpendicular direction. Contrary to classical wetting theory, static droplets in equilibrium appear elongated, oriented parallel to the stretch direction. Both effects arise from droplet-induced deformations of the substrate near the contact line.
Collapse
Affiliation(s)
| | - Qin Xu
- Department of Materials, ETH Zürich, 8093 Zürich, Switzerland
- Department of Physics, The Hong Kong University of Science and Technology, Hong Kong, China
| | - Stefanie Heyden
- Department of Materials, ETH Zürich, 8093 Zürich, Switzerland
| | - Nicolas Bain
- Department of Materials, ETH Zürich, 8093 Zürich, Switzerland
| | - Jacco H Snoeijer
- Physics of Fluids Group, Faculty of Science and Technology, Mesa+Institute, University of Twente, 7500 AE Enschede, Netherlands
| | - Eric R Dufresne
- Department of Materials, ETH Zürich, 8093 Zürich, Switzerland
| | - Robert W Style
- Department of Materials, ETH Zürich, 8093 Zürich, Switzerland
| |
Collapse
|