Direction, Shape, and Scale Dependence of Ice Adhesion on Topographical Wetting Gradients

In this work, a shear stress test is used to evaluate the ice adhesion strength on "as received", polished and micro/nanoengineered hierarchical superhydrophobic aluminium (produced via one-step laser etching) with fixed- and gradient-pitch structures. Due to the potential mismatch between the ice formation area and the wetting gradient length scale, the shear stress test method has been analysed in detail to understand its applicability to topographic gradients, since this could provide misleading results as compared with the application of this method to fixed-pitch topographic structured surfaces. To address this, the influence of the ice-surface contact area, as well as the mould shape and mould material, on the ice adhesion results, was observed for all samples. Moreover, the impact of the direction of the removal force was investigated on the wetting gradients. Key results are that topographically altered surfaces can be hydrophobic, but not icephobic; whereas non-altered surfaces are hydrophilic, but with much lower ice adhesion. Additionally, gradient surfaces were observed to provide hydrophobicity for most areas of the surface, while allowing removal of the ice column at lower forces from certain directions.