Investigating the effect of oil-infusion on the icephobicity of elastomer coatings

Abstract

The hazards of ice accumulation include damage to infrastructure, disruption of transportation, and even major accidents. Historically, the solution has been to de-ice surfaces by chemical, mechanical or thermal means. Anti-icing coatings are a proposed alternative which passively prevent ice accumulation. The icephobicity of a coating is assessed via the ice adhesion strength and freezing delay. Elastomer coatings infused with miscible oil have shown particularly low ice adhesion. However, there has been little investigation of the effect on freezing delay. The aim of this work is to provide a comprehensive study of the icephobicity of oil-infused elastomers to better understand the effect of oil-infusion.

Seven elastomer coatings were investigated: two PDMS (polydimethylsiloxane) coatings, four silicone-oil/PDMS coatings (two molecular weights of oil, at two concentrations – 25% and 50%), and a commercial coating (NuSil R-2180). Ice adhesion testing was performed via a push test method, in which ice frozen in acrylic cylinders on the coatings was displaced by a force probe. 100 repeat de-icing cycles were performed in a refrigerated laboratory at −10°C. Freezing delay was measured via visual observation of the time for a droplet of water to freeze, from deposition on the surface, and compared to a bare aluminium reference. The elastic modulus, contact angle, surface roughness and room temperature adhesion of the surfaces was characterised alongside the icephobicity testing.

Despite greater degradation over time, the oil-infused coatings exhibited consistently lower ice adhesion strengths than the non-oil infused coatings, less than 50% in most of the 100 de-icing cycles. De-icing did not cause significant damage or increase in ice adhesion strength of the oil-infused coatings, but the non-oil infused coatings exceeded the equipment load limit with increasing frequency, meaning they lose icephobicity. Fitting the data to models for interfacial cavitation and interfacial slippage showed a better correlation to interfacial slippage, and shear modulus had the strongest influence on adhesion strength. This understanding can assist future coating design. There was little difference in the freezing delay of the coatings, but all provided an improvement on bare aluminium. Measurements performed before and after adhesion testing showed a small decrease in freezing delay post-adhesion.

The effect of severe damage was investigated using specimens which were abraded with grit paper or cut by a scalpel. There was a slight increase in ice adhesion and small decrease in the freezing delay. Cryo-FIB/SEM showed a mixture of high and low conformation at the ice-coating interface. Recoating the surfaces restored the original performance of the coatings, which would allow for straightforward repair in practice. To better understand the mechanism by which oil-infusion lowers ice adhesion strength, a new method for investigating interfacial slippage was developed. Using a microtribometer mounted under an optical microscope, de-icing tests were performed on ice droplets. Fluorescent microparticles embedded in the top of the coatings were tracked during de-icing to monitor for polymer flow. Results were inconclusive in determining the presence of interfacial slippage; however, suggestions for further work are made.

The oil-infused elastomer coatings are shown to have excellent icephobicity. Their use in anti-icing applications lowers the ice adhesion strength while maintaining freezing delay of non-oil infused coatings. Their use would reduce de-icing requirements and lessen the energy, time and resources spent on removing surface ice from, for example, bare metals. They would also reduce damage caused by accumulation and detachment of heavy ice loads. Durability of oil-infused elastomers is also shown not to be a major concern: de-icing causes minimal damage, good icephobicity is maintained even with moderate-to-severe damage, and recoating damaged surfaces is an effective method of repair.