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A simple way to measure solid surface tension : theory and experiment

Chung-Yuen Hui Department of Mechanical and Aerospace Engineering, Cornell University, USA

The role of surface energy in determining mechanical properties such as adhesion, friction and fracture toughness is well known. In comparison, the role of the closely related surface mechanical property, surface tension or surface stress on mechanical properties is less studied. This is because the surface tension (stress) of solids can be very difficult to measure. In this talk, I will present a simple analysis which shows that the deformation caused by a liquid drop on a thin film can caused it to bulge by tens of microns. The deformed shape of the film is governed by tensions exerted by various interfaces and the solid film. 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, can be interpreted as the solid-fluid surface tension. These interfacial tensions are determined by experiments using PDMS (Polydimethylsiloxane) thin films with various non-swelling liquids.