Super-wetting enabled by an array of SU-8 micro-pillars etched with ion-beam

The wettability transition of an ion-beam-etched micro-pillar array surface is reported in the present study. The micro-pillar array, made of negative photoresist SU-8, was fabricated by ultraviolet lithography. The results indicate that the combination of the micro-pillar array and ion-beam etching technique can easily regulate surface wettability, which can be changed from hydrophobicity to super-hydrophilicity. Moreover, the super-hydrophilic property of the textured surface can be significantly affected by the etching time and etching energy, because the ion-beam etching could alter the shape and height of the micro-structure as well as the chemical composition of the surface. When a 2 µl water droplet spreads on the etched micro-pillar array surface, the contact angle (CA) decreases to almost 0° within 144 ms, indicating ultrafast spreading of the water droplet on the textured surface. It was found that the CA of the fabricated surface remained the same after two weeks' exposure in the air, showing undependable wettability stability of the textured surface. The results of the present study can open a gate for potential applications of proposed super-wetting surfaces for micro-fluidics and anti-counterfeiting technologies.