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Hauer L, Naga A, Badr RGM, Pham JT, Wong WSY, Vollmer D. Wetting on silicone surfaces. SOFT MATTER 2024; 20:5273-5295. [PMID: 38952198 DOI: 10.1039/d4sm00346b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/03/2024]
Abstract
Silicone is frequently used as a model system to investigate and tune wetting on soft materials. Silicone is biocompatible and shows excellent thermal, chemical, and UV stability. Moreover, the mechanical properties of the surface can be easily varied by several orders of magnitude in a controlled manner. Polydimethylsiloxane (PDMS) is a popular choice for coating applications such as lubrication, self-cleaning, and drag reduction, facilitated by low surface energy. Aiming to understand the underlying interactions and forces, motivated numerous and detailed investigations of the static and dynamic wetting behavior of drops on PDMS-based surfaces. Here, we recognize the three most prevalent PDMS surface variants, namely liquid-infused (SLIPS/LIS), elastomeric, and liquid-like (SOCAL) surfaces. To understand, optimize, and tune the wetting properties of these PDMS surfaces, we review and compare their similarities and differences by discussing (i) the chemical and molecular structure, and (ii) the static and dynamic wetting behavior. We also provide (iii) an overview of methods and techniques to characterize PDMS-based surfaces and their wetting behavior. The static and dynamic wetting ridge is given particular attention, as it dominates energy dissipation, adhesion, and friction of sliding drops and influences the durability of the surfaces. We also discuss special features such as cloaking and wetting-induced phase separation. Key challenges and opportunities of these three surface variants are outlined.
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Affiliation(s)
- Lukas Hauer
- Institute for Biology, Humboldt-Universität zu Berlin, 10115 Berlin, Germany
- Physics at Interfaces, Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany.
| | - Abhinav Naga
- Department of Physics, Durham University, DH1 3LE, UK
- Institute for Multiscale Thermofluids, School of Engineering, The University of Edinburgh, Edinburgh EH9 3FD, UK
| | - Rodrique G M Badr
- Institut für Physik, Johannes Gutenberg-Universität Mainz, Staudingerweg 7-9, 55099 Mainz, Germany
| | - Jonathan T Pham
- Department of Chemical and Environmental Engineering, University of Cincinnati, Cincinnati, 45221 OH, USA
| | - William S Y Wong
- Department of Applied Physics, School of Science, Aalto University, 02150 Espoo, Finland
| | - Doris Vollmer
- Physics at Interfaces, Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany.
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2
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Hartmann S, Diekmann J, Greve D, Thiele U. Drops on Polymer Brushes: Advances in Thin-Film Modeling of Adaptive Substrates. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2024; 40:4001-4021. [PMID: 38358424 DOI: 10.1021/acs.langmuir.3c03313] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/16/2024]
Abstract
We briefly review recent advances in the hydrodynamic modeling of the dynamics of droplets on adaptive substrates, in particular, solids that are covered by polymer brushes. Thereby, the focus is on long-wave and full-curvature variants of mesoscopic hydrodynamic models in gradient dynamics form. After introducing the approach for films/drops of nonvolatile simple liquids on a rigid smooth solid substrate, it is first expanded to an arbitrary number of coupled degrees of freedom before considering the specific case of drops of volatile liquids on brush-covered solids. After presenting the model, its usage is illustrated by briefly considering the natural and forced spreading of drops of nonvolatile liquids on a horizontal brush-covered substrate, stick-slip motion of advancing contact lines as well as drops sliding down a brush-covered incline. Finally, volatile liquids are also considered.
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Affiliation(s)
- Simon Hartmann
- Institut für Theoretische Physik, Universität Münster, Wilhelm Klemm Str. 9, D-48149 Münster, Germany
| | - Jan Diekmann
- Institut für Theoretische Physik, Universität Münster, Wilhelm Klemm Str. 9, D-48149 Münster, Germany
| | - Daniel Greve
- Institut für Theoretische Physik, Universität Münster, Wilhelm Klemm Str. 9, D-48149 Münster, Germany
| | - Uwe Thiele
- Institut für Theoretische Physik, Universität Münster, Wilhelm Klemm Str. 9, D-48149 Münster, Germany
- Center of Nonlinear Science (CeNoS), Universität Münster, Corrensstr. 2, 48149 Münster, Germany
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3
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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.
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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
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Nekoonam N, Vera G, Goralczyk A, Mayoussi F, Zhu P, Böcherer D, Shakeel A, Helmer D. Controllable Wetting Transitions on Photoswitchable Physical Gels. ACS APPLIED MATERIALS & INTERFACES 2023. [PMID: 37217181 DOI: 10.1021/acsami.2c22979] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Softness plays a key role in the deformation of soft elastic substrates at the three-phase contact line, and the acting forces lead to the formation of a wetting ridge due to elastocapillarity. The change in wetting ridge and surface profiles at different softness has a great impact on the droplet behavior in different phenomena. Commonly used materials to study soft wetting are swollen polymeric gels or polymer brushes. These materials offer no possibility to change the softness on demand. Therefore, adjustable surfaces with tunable softness are highly sought-after to achieve on-demand transition between wetting states on soft surfaces. Here, we present a photorheological physical soft gel with adjustable stiffness based on the spiropyran photoswitch that shows the formation of wetting ridges upon droplet deposition. The presented photoswitchable gels allow the creation of reversibly switchable softness patterns with microscale resolution using UV light-switching of the spiropyran molecule. Gels with varying softness are analyzed, showing a decrease in the wetting ridge height at higher gel stiffness. Furthermore, wetting ridges before and after photoswitching are visualized using confocal microscopy, showing the transition in the wetting properties from soft wetting to liquid/liquid wetting.
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Affiliation(s)
- Niloofar Nekoonam
- Laboratory of Process Technology, Department of Microsystems Engineering (IMTEK), University of Freiburg, 79110 Freiburg im Breisgau, Germany
| | - Grace Vera
- Laboratory of Process Technology, Department of Microsystems Engineering (IMTEK), University of Freiburg, 79110 Freiburg im Breisgau, Germany
- Freiburg Materials Research Center (FMF), University of Freiburg, 79104 Freiburg im Breisgau, Germany
| | - Andreas Goralczyk
- Laboratory of Process Technology, Department of Microsystems Engineering (IMTEK), University of Freiburg, 79110 Freiburg im Breisgau, Germany
| | - Fadoua Mayoussi
- Laboratory of Process Technology, Department of Microsystems Engineering (IMTEK), University of Freiburg, 79110 Freiburg im Breisgau, Germany
| | - Pang Zhu
- Laboratory of Process Technology, Department of Microsystems Engineering (IMTEK), University of Freiburg, 79110 Freiburg im Breisgau, Germany
| | - David Böcherer
- Laboratory of Process Technology, Department of Microsystems Engineering (IMTEK), University of Freiburg, 79110 Freiburg im Breisgau, Germany
| | - Ahmad Shakeel
- Laboratory of Process Technology, Department of Microsystems Engineering (IMTEK), University of Freiburg, 79110 Freiburg im Breisgau, Germany
- Freiburg Materials Research Center (FMF), University of Freiburg, 79104 Freiburg im Breisgau, Germany
| | - Dorothea Helmer
- Laboratory of Process Technology, Department of Microsystems Engineering (IMTEK), University of Freiburg, 79110 Freiburg im Breisgau, Germany
- Freiburg Materials Research Center (FMF), University of Freiburg, 79104 Freiburg im Breisgau, Germany
- Freiburg Center of Interactive Materials and Bioinspired Technologies (FIT), University of Freiburg, 79110 Freiburg im Breisgau, Germany
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Sekhar S, Sharma A, Shankar V. Instability and rupture of ultrathin freestanding viscoelastic solid films. Phys Rev E 2022; 106:024803. [PMID: 36109925 DOI: 10.1103/physreve.106.024803] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2022] [Accepted: 08/12/2022] [Indexed: 06/15/2023]
Abstract
We analyze the instability of viscoelastic solid freestanding thin films under the influence of van der Waals forces using linear stability analysis and nonlinear simulations. Linear stability analysis shows that the zero-frequency elastic modulus governs the onset of instability and stabilizes the film beyond a critical value analogous to thin supported viscoelastic solid films. However, for freestanding solid films, the critical shear modulus is found to be independent of surface tension, unlike that of thin supported viscoelastic solid films. It is further shown that freestanding viscoelastic solid films with higher moduli can be destabilized for a given film thickness and Hamaker constant compared to supported solid films. In contrast to thin viscoelastic liquid films where the growth rate is enhanced due to elastic effects but length scale is unaltered, freestanding films with solidlike viscoelasticity show a retarded growth rate and enhanced length scale. The presence of solidlike viscoelasticity has a stabilizing effect and affects all the key aspects of instability such as critical wave number, dominant wave number, and maximum growth rate. We numerically solve the set of coupled nonlinear evolution equations for film thickness and tangential displacement in order to elucidate the dynamics of film rupture. Our simulations show that, consistent with the linear stability predictions, an increase in the elastic modulus delays film rupture. The dynamics exhibits self-similarity in the vicinity of film rupture and the film thins as (t_{r}-t)^{3/4}, where t_{r} is the rupture time and t_{r}-t is the time remaining until film rupture. The scaling exponent 3/4 obtained for a thin freestanding viscoelastic solid film is significantly greater than the scaling exponent (1/3) for a thin freestanding viscous film.
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Affiliation(s)
- Satya Sekhar
- Department of Chemical Engineering, Indian Institute of Technology Kanpur, Uttar Pradesh 208016, India
| | - Ashutosh Sharma
- Department of Chemical Engineering, Indian Institute of Technology Kanpur, Uttar Pradesh 208016, India
| | - V Shankar
- Department of Chemical Engineering, Indian Institute of Technology Kanpur, Uttar Pradesh 208016, India
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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: 4] [Impact Index Per Article: 2.0] [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.
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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
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