Superhydrophobic surfaces with embedded protective sawtooth ring microstructures

Despite the achievements in superhydrophobic surface obtained via geometrically uniform micro-nano scale surface texture, the mechanical robustness of superhydrophobic surfaces remains a challenge where service conditions involve solid-body contact. We introduce a unique sawtooth-ring protective microstructure design as an integrated shield for underlying superhydrophobic micro-pillar arrays. The sawtooth-ring design minimizes the areal occupancy of the surface and merges directly with the anti-wetting micro-pillar array, giving rise to an integrated micro-structure. The integrated surface micro-structure has been fabricated in an intermediate polymer mold via an innovative two-step thermal nanoimprinting process. The integrated sawtooth ring and micro-pillar array have been replicated on UV polymerized resin, thermally cured polydimethylsiloxane (PDMS) and solvent cast polycarbonate (PC) using the intermediate polymer mold. The post-compression water contact angle results demonstrate the reliance of the sawtooth ring design on the underlying material's resistance to plastic yield. This reliance can be met either in the form of relatively high yield stress, as is the case with PC or in the form of a large elastic strain tolerance, as is the case with PDMS. In both cases, compressive testing of sawtooth ring protected anti-wetting surfaces resulted in the retention of the Cassie-Baxter 2-component wetting state and negligible degradation in their respective contact angles.