Precise tip shape transformation of nanopillars for enhanced dry adhesion strength
We present a simple, yet robust, technique for controlling the tip geometry of nanopillars by utilizing a two-step process of partial photopolymerization of UV-curable polyurethane acrylate (PUA) resin and subsequent tip shape modification. With this technique, head structures of nanopillars were precisely transformed from hemispherical to protruding, mushroom-like tips without any loss in structural integrity of the nanopillars. Nanoscopic and macroscopic adhesion measurements for angled nanopillars with modified tips demonstrated that mushroom-like structures fabricated by our approach could greatly enhance adhesion strengths as compared to unmodified, round head structures. Also, directional adhesion characteristics of angled nanopillars were maintained regardless of tip shapes.