Energy Efficient De-Icing by Superhydrophobic and Icephobic Polyurethane Films Created by Microstructuringand Plasma-Coating 2015-01-2159

As known de-icing methods use a high amount of energy or environmentally harmful chemicals, research has focused lately on passive de-icing by functional surfaces with an improved removal of ice (de-icing) or a reduced formation of it (anti-icing).

Inspired by the Lotus plant leaf, a “superhydrophobic” surface can be produced by the combination of a hierarchical micro/nanoscale roughness and a hydrophobic surface coating. By a hot stamping process we have generated differently shaped microstructures (cylinders, ellipses) on polyurethane (PU) films which were afterwards coated by a plasma enhanced chemical vapor deposition (PECVD) process with thin, hydrophobic fluorocarbon films. This combination of methods could be a process for the production of large area functionalized films. PU films are suitable for outdoor use, because they are resistant against erosion and UV radiation. The films can be glued to different geometries and can easily be exchanged if damaged.

Analysis of the surface chemistry of the thin films was done by XPS (X-ray photoelectron spectroscopy) and the thickness was measured with ellipsometry. The microstructures were examined by digital light microscopy and confocal laser scanning microscopy. The wetting analysis was done by dynamic contact angle measurements with water. The contact angle (CA) measurements clearly show the water repellency of the plasma coatings (advancing CA = approx. 120°), the hydrophobicity could be further improved by microstructuring (advancing CA = approx. 150°). Very small contact angle hystereses of around 1° to 3° were measured, which enables an easy roll-off of water drops. For determination of the ice adhesion force water droplets were frozen on the produced surfaces and the force for removal was then measured by pull-off tests. The results show a reduced ice adhesion of below 200 kPa for the functional surfaces.