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Memon, Halar (2021) Research and development of polyurethane icephobic composite coatings. PhD thesis, University of Nottingham.

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Abstract

Ice accretion over critical engineering structures could lead to costly hazards, and ice prevention is an energy-intensive activity, thus making the applications complicated and inefficient. A more promising and specific strategy is to deploy passive ice protection approaches such as durable coatings that allow the super-cooled droplets to slide off before icing (anti-icing), or that detaches the developed ice completely (de-icing). The main aim of this project was to research and develop new types of polyurethane-based icephobic coatings for potential applications in the aerospace and wind energy industries. The experimental work was planned to offer balanced research outputs on the fundamental aspects of icephobicity studies and to impart the acquired knowledge for the fabrication and investigation of novel durable icephobic materials/surfaces.

At first, fundamental studies relating to surface icephobicity and icephobicity were carried out. A systematic reduction of ice adhesion with the decrease in surface roughness was demonstrated across all the studied material types, i.e. metallic surfaces and polymeric coatings with different surface wettability. If the surface bears a similar surface roughness, then wettability plays a deciding role in reducing the ice adhesion. A surface with higher roughness provides an increased number of possible ice anchoring points and the ice anchoring mechanism was further validated under in-situ icing observation. Furthermore, the variation in response to surface characteristics in icephobicity evaluation methods was also investigated. Centrifugal and horizontal push (shear) methods suggested a linear relationship of ice adhesion strength with surface roughness, whereas the tensile (normal) method indicated an inverse curvilinear relationship with contact angle hysteresis. Apart from the de-icing evaluation, water droplet freezing delay suggested a direct correlation with surface roughness and the visual examination of frost accumulated samples suggested a reduction in ice densification on the smoothened surfaces, indicating a weakened bond between the ice/solid interfaces. The results offer crucial information on the pre-selection of testing regimes to accurately measure the performance of icephobic materials.

In the second part, several polyurethane-based nanocomposite, fibre-reinforced, and liquid-infused coatings were developed and investigated to understand the deteriorating behaviour of the coatings under impinging erosion tests and the subsequent impact on ice adhesion. The durability analysis on polyurethane composite coatings indicated that the incorporation of fillers was effective in reducing the number of possible ice anchoring points, and after the impingement, the icephobic performance was retained by either lowering surface roughness or by minimising surface deterioration. The reinforcement was effective such that the change in surface roughness was reduced by a factor of 4, compared to the pure polyurethane coatings under erosion impact. To provide an exceptional icephobic response, glycerol-infused fibre-reinforced polyurethane (GIFRP) coatings was proposed by mimicking the fibrous structure of cetacean skin. Instead of hosting the lipid proteins, the coatings were infused with glycerol, a known cryoprotectant to induce the supercooling of water, a strategy inspired by chionophiles, to prevent freezing. The inclusion of glycerol delayed water droplet freezing duration by 659%, while negligible frost accumulated on the fabricated coatings in the anti-icing tests. In addition to the promising anti-icing performance, the incorporation of fibrous structure has proven to be beneficial for infused-liquid replenishment and the slow-releasing capabilities of GIFRP coatings. Minimised surface deterioration and the continued presence of glycerol on GIFRP coatings demonstrated a small increase in ice adhesion from 0.22 kPa to 0.77 kPa after the erosion tests, one of the lowest values reported in literature after substantial surface damage. The concept inspired by cetacean skin and the cryoprotective features of chionophiles was instrumental in keeping the ice adhesion under 1 kPa after erosion impact.

Item Type:	Thesis (University of Nottingham only) (PhD)
Supervisors:	Hou, Xianghui Davide, De Focatiis Kwing-So, Choi
Keywords:	Polyurethane, Icephobic, Composite coatings
Subjects:	T Technology > TS Manufactures
Faculties/Schools:	UK Campuses > Faculty of Engineering UK Campuses > Faculty of Engineering > Department of Mechanical, Materials and Manufacturing Engineering
Item ID:	66394
Depositing User:	Memon, Halar
Date Deposited:	31 Dec 2021 04:40
Last Modified:	31 Dec 2021 04:40
URI:	https://eprints.nottingham.ac.uk/id/eprint/66394

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