Stable Biomimetic Superhydrophobic Surfaces Fabricated by Polymer Replication Method from Hierarchically Structured Surfaces of Al Templates

Abstract

We have developed a simple, efficient, and highly reproducible method to fabricate the large-area biomimetic superhydrophobic polymer surfaces having hierarchical structures of micrometer-sized irregular steps and nanometer-sized fibrils. Commercial Al plates (99.0%) were etched using Beck's dislocation etchant (mixture of HCl and HF) for different time periods in order to alter the structure of the etched Al surfaces from micrometer-sized to highly rough nanometer-sized irregular steps. These hierarchical structures could be easily replicated onto the surface of various thermoplastic polymer plates from the etched Al templates by applying heat and pressure; many polymer replicas without any significant deviations from each other could be duplicated from the same etched Al master templates. All of thermoplastic polymer replicas having hierarchical structures exhibited superhydrophobic properties with water contact angles of larger than 150 degrees. Especially, the surfaces of the high-density polyethylene (HDPE) replicas having nanometer-sized curled strands exhibited superhydrophobicity with a static water contact angle of approximately 160 degrees and a sliding angle of less than 2 degrees. These superhydrophobic HDPE replicas having nanometer-sized curled strands showed excellent stability after being exposed to various organic solvents and aqueous solutions of various pH.