Adhesion of biologically inspired oil-coated polymer micropillars

This paper presents the performance of a beetle foot-hair inspired polymer microfibrillar wet adhesive. Micropatterned poly(dimethylsiloxane) arrays of low aspect ratio cylinders are fabricated using optical lithography and molding techniques. A thin layer of viscous silicone oil is applied via stamping. The synthetic micropillar wet adhesive is characterized with a custom tensile adhesion measurement setup by varying the retraction speed, preload, contact time, oil viscosity and oil volume. An enhancement of adhesion up to 25% over the same micropattern without any applied liquid is demonstrated on a smooth substrate. A thicker silicone layer is shown to increase the adhesion of the micropillars by a factor of almost 6 on a 650 nm root-mean-square rough slightly polished aluminum surface. A model is also developed that combines surface tension and dynamic viscous forces to predict the adhesive performance. This model matched experimental data with reasonable tuning of only a single parameter. These results are used to propose further advancements in the design and fabrication of synthetic wet micropatterned adhesives. (C) Koninklijke Brill NV, Leiden, 2008.