Nano-textured polymer surfaces with controlled wetting and optical properties using plasma processing

Abstract

Wettability control is of great importance in many applications, from manufacturing of water repellent surfaces to droplet frictionless motion in microfluidics, and biocompatibility tuning. Wetting or repellent behaviour is governed by both surface chemistry and topography. In particular, super-hydrophobicity is attained by combining high-aspect-ratio (HAR) geometrical characteristics with low surface energy coatings. In this study we continue our research efforts pertaining a novel, simple, generic and fast technique to fabricate stable super-hydrophobic, yet transparent surfaces by means of high-density plasma etching and deposition. A High Density Plasma reactor is used to treat two different kind of polymers; an organic one (PMMA) and a hybrid one (PDMS). Different plasma chemistries specific to each polymer are implemented to etch the surfaces followed by a fluorocarbon deposition to control the surface roughness and the surface chemistry respectively. AFM is used to characterise morphology and water contact angle measurements to characterise wetting properties. We demonstrate high aspect ratio pillars with height ranging from ca. 350 nm to several microns depending on the processing time, and contact angles of 150° with hysteresis lower than 10°. Surfaces with pillars shorter than 400 nm are simultaneously transparent.