Bioinspired Surfaces for Super Liquid and Ice Repellency
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Abstract
Surfaces with ultralow adhesion to liquids and solids are of great interest for both fundamental research and practical applications, from passive removal of highly wetting liquids to anti-icing. This dissertation aims to investigate and develop bioinspired methods for achieving super- repellency and addressing issues related to the high adhesion of liquids and ice on surfaces. In this dissertation, the limitations of the current state-of-the-art superomniphobic surfaces (rely on air lubricant) and liquid-infused surfaces (rely on liquid lubricant) are discussed followed by the proposal of a new design of superomniphobic surface, which mitigates the dependence on stringed nanoparticles and can be easily converted into a liquid-infused surface with a simple one-step process. Drawing inspiration from various bio-inspired design strategies, along with liquid repellency anti-icing has been explored in broad aspects: (1) Delay of frost propagation through the meniscus-mediated spontaneous movement of droplets on liquid-infused surfaces. Surface tension forces generated by the hydrophilic oil meniscus of a large water droplet on a hydrophilic liquid-infused surface efficiently pull neighboring tiny droplets with a diameter < 20 m from all directions, causing them to climb and coalesce. This creates a dynamic length separation between water droplets and a neighboring frozen droplet, which eventually delays frost bridging. This is supported by a theoretical model to characterize the dynamically changing inter-droplet gaps. (2) A new design of quasi-liquid surfaces is demonstrated to address the durability challenges of current state-of-the-art super-repellent surfaces in terms of liquid repellency and ice adhesion. Inspired by cilia in human lungs, quasi-liquid lubrication is achieved by grafting flexible polymer molecules on a flat solid substrate. The mobile polymer chains behave like a liquid layer and significantly reduce the interfacial adhesion between the substrate and ice, resulting in ultralow ice adhesion. (3) The adhesion mechanics of ice on different substrates at high supercooling are studied. Due to a sudden drop in temperature from - 10 to -60ºC, ice cracking occurs and can be categorized as large, intermediate, and no cracks on aluminum, glass, and polycarbonate respectively based on the thermal properties of the substrate. A theoretical model is proposed to quantify the number of cracks formed at the ice-substrate interface due to thermo-mechanical stresses. Finally, an analogy is made between the interfacial cracks, total crack length, and the reduction in ice adhesion. Overall, this dissertation provides insights into bioinspired design strategies for super-repellency, with potential applications in liquid repellency and anti-icing.