(104j) Influence of Humidity on Gecko-Inspired Adhesives

Geckos have developed foot pads that allow them to maintain their supreme climbing ability despite vast differences in environment, from dry desert to humid rainforest. Successful gecko-inspired mimics should exhibit necessary adhesive and frictional performance across a similarly diverse range of climates. In this work we focus on the effect of relative humidity (RH) on the frictional adhesion behavior of gecko-inspired adhesive pads. A surface forces apparatus (SFA) was used to quantitatively measure adhesive and frictional forces of an anisotropic (tilted half-cylinder) microfibrillar polydimethylsiloxane (PDMS) surface against a smooth hemispherical glass disk at varying levels of relative humidity from 0-100 %, including fully submerged under water. The results are also compared with a flat PDMS control. Changes in the relative contributions of van der Waals and capillary forces with shearing direction and relative humidity have significant implications for frictional adhesion and â??reversibilityâ??. These results can be extended to formulate design principles for reversible adhesive platforms in humid environments.