We report direct measurement of surface deformation in soft solids due to their surface tension. Gel replicas of poly(dimethysiloxane) masters with rippled surfaces are found to have amplitudes that decrease with decreasing gel modulus. Surface undulations of a thin elastomeric film are attenuated when it is oxidized by brief exposure to oxygen plasma. Surface deformation in both cases is modeled successfully as driven by surface tension and resisted by elasticity. Our results show that surface tension of soft solids drives significant deformation, and that the latter can be used to determine the former.

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We measured the shape change of periodic ridge surface profiles in gelatin organogels resulting from deformation driven by their solid-vapor surface stress. A gelatin organogel was molded onto poly-dimethylsiloxane (PDMS) masters having ridge heights of 1.7 and 2.7 μm and several periodicities. Gel replicas were found to have a shape deformed significantly compared to their PDMS master. Systematically larger deformations in gels were measured for lower elastic moduli. Measuring the elastic modulus independently, we estimate a surface stress of 107 ± 7 mN m(-1) for the organogels in solvent composed of 70 wt% glycerol and 30 wt% water. Shape changes are in agreement with a small strain linear elastic theory. We also measured the deformation of deeper ridges (with height 13 μm), and analysed the resulting large surface strains using finite element analysis.