Abstract

In this paper we present a method to create a hydrophobicity gradient on the surface of a Polydimethylsiloxane (PDMS) dry adhesive. The method consists of the partial silanization of the surface of the dry adhesive by Chemical Vapour Deposition (CVD) of octadecyltrichlorosilane (OTS). The partial silanization of the surface of the sample results in a hydrophobic to hydrophilic gradient across the surface of the dry adhesive. The resulting change in hydrophobicity across the surface of the dry adhesive results in the uphill motion of a droplet of water, which appears to be directly proportional to the area of contact between the droplet and the adhesive. Normal adhesion testing is performed to quantify the effect of the hydrophobic gradient across the surface of the sample. While a variation in adhesion strength across the sample is measured, the adhesive properties are only minimally affected by the silanization, and the motion of the droplet of water doesn't cause any loss of adhesion.