Fabrication of hairy polymeric films inspired by geckos: Wetting and high adhesion properties

Abstract

In this paper, we report a facile and efficient method for fabricating gecko-inspired, hairy hard poly(dimethylsiloxane) (h-PDMS) structures, composed of nanopillars with controllable lengths. The structures are generated by utilizing an anodic aluminum oxide (AAO) membrane as a replication template. For easy handling of the replicated h-PDMS films, the vinyl-terminated glass substrate is used. The cross-linking between the vinyl moieties on the glass surface and methylhydrosiloxanes, one of the h-PDMS components, makes it easy to transfer the molded h-PDMS layer from the AAO template to the glass. The resulting hairy h-PDMS-coated glass surface shows both the static water contact angle as high as 150.5 degrees +/- 0.4 degrees (superhydrophobicity) and high adhesion to water. A water droplet placed on the h-PDMS surface does not slide, even when the surface is tilted vertically or turned upside down. We believe that the densely packed h-PDMS nanopillars (2.6 x 10(6) pillars mm(-2)) are the key contributor to the observed high adhesion, presumably by generating large van der Waals' forces from the large surface area in very close contact with water. The adhesion force of the surface is found to be strong enough to catch a water droplet that rolls down fast on a tilted self-cleaning surface. In addition to water, the wetting and high adhesion properties of the molded nanopillar h-PDMS films are also investigated with several organic liquids.