title: Solid surface tension measured by a liquid drop under a solid film.
abstract: We show that a drop of liquid a few hundred microns in diameter placed under a solid, elastic, thin film (∼10 μm thick) causes it to bulge by tens of microns. The deformed shape is governed by equilibrium of tensions exerted by the various interfaces and the solid film, a form of Neumann's triangle. Unlike Young's equation, which specifies the contact angles at the junction of two fluids and a (rigid) solid, and is fundamentally underdetermined, both tensions in the solid film can be determined here if the liquid-vapor surface tension is known independently. Tensions in the solid film have a contribution from elastic stretch and a constant residual component. The residual component, extracted by extrapolation to films of vanishing thickness and supported by analysis of the elastic deformation, is interpreted as the solid-fluid surface tension, demonstrating that compliant thin-film structures can be used to measure solid surface tensions.
authors.affiliation: Department of Chemical Engineering and Bioengineering Program, Lehigh University, Bethlehem, PA 18015, USA.
authors.forename: Nichole
authors.initials: N
authors.lastname: Nadermann
authors.forename: Chung-Yuen
authors.initials: CY
authors.lastname: Hui
authors.forename: Anand
authors.initials: A
authors.lastname: Jagota
keywords: membrane; soft materials; surface stress; wetting