The penguin feather as inspiration for anti-icing surfaces

Abstract

Understanding how to influence ice adhesion to structures and prevent icing catastrophes is a paramount research question. Conventional industrial anti-icing methods are active, requiring an energy source. However, active strategies are energy intensive. Passive anti-icing surfaces have thus become an area of engineering interest. Such strategies, like low surface energy chemical coatings, produce highly anti-icing surfaces on a lab-scale but they have not succeeded in industrial applications. They lack efficacy over repeated icing/de-icing cycles and their materials are unsuited for harsh environments. The body feather of the sub-Antarctic Gento penguin Pygoscelis papua, which ornithologists note is perpetually free of ice despite its freezing environment, serves as a compelling source of passive anti-icing biomimetic inspiration which may overcome these aforementioned deficiencies. Through studying these feathers, it has become clear that two aspects of anti-icing (water-shedding and ice-shedding) are addressed in distinct ways by the Gentoo penguin. The water-shedding functionality of the feathers is derived from an air cushion created by the wire-like microstructure of the feather and is augmented by nano-scale grooves in the feather coated in preen oil. The preen oil is necessary to maintain water-shedding functionality, however once removed the ice-shedding functionality of the feathers is maintained. The ice-shedding functionality appears to be derived from wire-like morphology of the penguin body feather barbs and barbules which induce cracks that are easily opened at the ice-feather interface. Such a design strategy shows promise in addressing the common failings of passive systems. These anti-icing strategies were then tested on metallic biomimetic substrates. The barb structure of the penguin body feather was mimicked using ultra-fine woven stainless-steel wire cloth. Some stainless-steel wire cloths were laser machined to mimic the texturing and surface chemistry of the feathers. These cloths were indeed hydrophobic like the feathers. Both stainless-steel wire cloths had significantly reduced ice adhesion strengths compared to those of the flat monolithic stainless-steel sample. The laser-machined wire cloth had an ice adhesion strength of 63 ± 10 kPa compared to 603 ± 236 kPa for the flat sample. This both indicates that the ice-shedding capabilities of the sample are imparted by the structure and further strengthens the argument that water-shedding and ice-shedding are distinct phenomena that need to be addressed with two separate design strategies.