Optically transparent superhydrophobic polydimethylsiloxane by periodic surface microtexture

To achieve surface microtexture on poly(dimethysiloxane) (PDMS), laser processing of an aluminum sample and replication through hot embossing to a polycarbonate sheet, followed by PDMS thermal curing on both the etched aluminum and embossed polycarbonate is used. Surface topology measurements of the microtextured aluminum reveal microtexture height near 12 μm, with slightly smaller microtexture height on the replicated surfaces. These PDMS samples exhibit optical transparency between 43% and 72% while retaining static contact angles above 150°, as the percent area without microtexture is increased from 53.8% to 81%. While samples replicated from the aluminum master exhibit roll-off angles of below 2°, samples produced using a PC master exhibit an almost complete loss of roll-off angle performance. This is a consequence of the microtexture profile being inverted at each embossing step. Optical analysis of evaporating water droplets revealed a strong pinning force at the smooth to microtexture interface, which also affects the observed roll-off angle. Samples with an untextured surface area above 81% exhibit a transition in wetting dynamics, resulting in a decrease in the static contact angle to near 130° and a change in the roll-off angle to values near 65° as exhibited on a smooth PDMS surface. The fabrication process is found to be repeatable over many months, without degradation in performance of the microtexture master or PDMS samples.