Development of self-lubricating icephobic coatings

Ice formation affects the performance of numerous industrial components, including aircraft wings, spacecraft, and power transmission cables. Particularly, ice development on airplane parts increases drags and fuel consumption. A large number of studies have been carried out to reduce ice adhesion by developing passive methods, such as icephobic coatings, and active ice removal approaches, like mechanical vibration or chemical. Despite remarkable recent breakthroughs in producing icephobic coatings with very low adhesion, passive ice removal needs higher coating durability during mechanical ice detachment. Developing a durable and efficient icephobic coating plays a vital role in the aviation industry due to the adverse impact of ice formation. On the other hand, most of the existing icephobic coatings have a considerable level of complexity in the coating application and limitations in terms of mechanical durability and robustness during deicing cycles. This study aims to evaluate the effect of Polytetrafluoroethylene (PTFE) solid lubricant on the ice adhesion strength. In this order, glaze and mixed atmospheric ice was formed in an icing wind tunnel (IWT) and a custom-made ice adhesion test rig was designed and manufactured to measure the ice shear strength. The first part of this study mainly aims to qualitatively evaluate the icephobicity performance of a PTFE solid lubricant film with a custom-built push-off test device in different icing conditions utilizing a wind tunnel. The adhesion reduction factor (ARF) of the film has been assessed in comparison to a bare aluminum alloy substrate (Al 6061). The impact of surface energy was investigated by comparing the Water Contact Angle (WCA), the Contact Angle Hysteresis (CAH), and the pull-off force of PTFE solid lubricant and Al with an Atomic Force Microscope (AFM). The collected results of ice shear adhesion on the PTFE solid lubricant film confirmed that this film reduced the ice adhesion significantly at various substrate temperatures and surface roughness compared to the bare Al 6061 substrate. An interfacial detachment mechanism appears to be interfacial blisters appearing to form at the center of the ice, and with continued application of shear force, most of the energy injected would be distributed throughout the blisters, ultimately causing detachment. When comparing the adhesion of ice to PTFE solid lubricant and bare aluminum with different roughness, the ARF value was 1.62 for 0.3 µm and 1.36 for 1 µm. After ice adhesion was examined at temperatures between -2 ˚C and -10 ˚C, the film also showed the least amount of ice adhesion at -6 ˚C with an ARF of 3.41. In the second part of this study, the suspension plasma spray (SPS) technique, which is well-known for its robustness and dual-scale characteristics in ice accretion analysis, was used to apply a TiO2 coating on a stainless steel substrate. Then, three different types of samples (filled, partially-filled, and overfilled) were produced by brushing a layer of PTFE solid lubricant film on the hierarchical structure of the TiO2-coated substrates, and their icephobicity and mechanical toughness were assessed. The amount of the accreted ice was evaluated to indicate the anti-icing properties. The wettability parameters, including static water contact angle and contact angle hysteresis, were measured to determine the water mobility and surface energy. Ice shear adhesion on the PTFE solid lubricant film and its mechanical durability was evaluated by measuring the ice shear strength for almost twenty icing-deicing cycles. After every five cycles, the roughness parameters and the images taken from the surface of the samples were compared. The combination of the PTFE solid lubricant film and the TiO2 coating reduced ice adhesion by 70-90% compared to that on the bare aluminum substrate. The results showed that applying a uniform layer of the PTFE solid lubricant film on dual-scale TiO2 coating significantly decreased the ice adhesion and maintained mechanical durability for 25 dicing cycles, making this combination a promising candidate for dicing approaches