Issue 27, 2012

Static wetting on deformable substrates, from liquids to soft solids

Abstract

Young's law fails on soft solid and liquid substrates where there are substantial deformations near the contact line. On liquid substrates, this is captured by Neumann's classic analysis, which provides a geometrical construction for minimising the interfacial free energy. On soft solids, the total free energy includes an additional contribution from elasticity. A linear-elastic model incorporating an out-of-plane restoring force due to solid surface tension was recently shown to accurately predict the equilibrium shape of a thin elastic film due to a large sessile droplet. Here, we extend this model to find substrate deformations due to droplets of arbitrary size. While the macroscopic contact angle matches Young's law for large droplets, it matches Neumann's prediction for small droplets. The cross-over droplet size is roughly given by the ratio of the solid's surface tension and elastic modulus. On thin substrates at this cross-over, the macroscopic contact angle increases, indicating that the substrate is effectively less wetting. For droplets of all sizes, the microscopic behaviour near the contact line follows the Neumann construction giving local force balance.

Graphical abstract: Static wetting on deformable substrates, from liquids to soft solids

Article information

Article type
Paper
Submitted
07 Mar 2012
Accepted
11 May 2012
First published
01 Jun 2012

Soft Matter, 2012,8, 7177-7184

Static wetting on deformable substrates, from liquids to soft solids

R. W. Style and E. R. Dufresne, Soft Matter, 2012, 8, 7177 DOI: 10.1039/C2SM25540E

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