Self-cleaning Effects of Biomimetic Dry Adhesives

In this paper, we investigated the self-cleaning effects of biomimetic dry adhesives, which are made of e-beam photoresist and carbon nanotubes (CNT). Although the photoresist and the CNT are both intrinsically hydrophilic, superhydrophobic behavior was obtained when they were patterned or synthesized into nano-fibrils. The intrinsic hydrophilicity indicates that these materials possess sufficient surface energy for mimicking gecko foot-hairs as dry adhesives. The entrapped air between the nano-fibrils significantly decreases the contact area with small particles and enhanced the well-known lotus effects. Two methods are presented to facilitate this enforced hydrophobicity. First, nano-gaps on an e-beam photoresist surface are patterned with different contact area ratios. The experimental results show that it follows the theoretical prediction of hydrophobic behavior with the existence of nano-gaps. Second, carbon nanotubes are deposited with the assistance of water vapor on an oxidized silicon surface. Contact angle as large as 157 degree has been achieved on the oxide surface when the water vapor was optimized for the maximum density of CNT