Roll-to-Roll Hot Embossing of High Aspect Ratio Micro Pillars for Superhydrophobic Applications

Many surfaces in nature such as the lotus leaf, cicada wings, water spider legs and gecko feet have attracted attention due to their inherent superhydrophobicity and self-cleaning properties. These surfaces are characterized by water contact angles greater than 150 degrees and contact angle hysteresis < 10 degrees. In this work, a continuous fabrication methodology for production of such superhydrophobic surfaces consisting of well-ordered micro-pillar structures (aspect ratio greater than 1 (1.3)) on a large area polyamide film using roll-to-roll hot embossing process was demonstrated. It was found that the temperature played a significant role in replication. Incomplete replication was observed in regime 1 (150 to 155 degrees C) and the height of replication was influenced by nip pressure and roll speed due to viscosity variations. In contrast, complete replication was seen in regime 2 (190 to 195 degrees C) and the height of replication was insensitive to nip pressure and roll speed due to a fairly constant viscosity value. The embossed polyamide surface, once coated with a low surface energy 1H, 1H, 2H, 2H-perfluorooctyltrichlorosilane (PFTS) monolayer, showed super-repellant characteristics with respect to water and demonstrated a successful manufacturing approach to fabricate superhydrophobic surfaces.