Design Of Superrepellent Composite Coatings And Their Properties

The study of interfacial interactions of coating materials with fluids is important in the field of drag reduction,liquid separations,and many other chemical processes.However,conventional coatings often have high surface energy and thus strong interactions with surrounding liquids,which can cause serious surface staining and/or corrosion,limiting their practical applications.Superrepellent coatings are thin films that can durably repel a spectrum of liquids such as aqueous solutions,oil,and organic liquids,displaying ultrahigh contact angles(>150°)and ultralow roll-off angles(<10°),and are thereby of significance in chemical shielding,fluid transportation,heat transfer,and selective separations.Therefore,the development of high-performance(low adhesion,high durability,and broad-spectrum liquid rejection)superrepellent surfaces is important in the upgrading and the innovation of the national chemical industry.Chapter Two employs all-atom molecular dynamics(MD)simulations in the study of the binary coating system composed of fluorinated polyhedral oligomeric silsesquioxanes(POSS)and poly(isopropyl acrylamide)(PNIPAM).Specifically,the inter-spacing of species in the coating system,interaction energy,contact area,and pore size distributions are systemically studied to evaluate the feasibility of constructing homogeneous and heterogeneous superrepellent coatings.Experimental results are in good agreement with the MD simulations,indicating that the proposed binary component-based coating strategy can effectively combine the beneficial characteristics of the two precursors,which thereby serves as the framework and research method for engineering coatings with desirable surface properties.Chapter Three studies the construction,analysis,and application of a homogenous superrepellent coating composed of POSS and a cyanoacrylate binder,both experimentally and computationally.The POSS and the polymeric binder provide the required low surface energy and high adhesion to the substrate,respectively.Driven by high-pressure spraying,the polymeric binder can firmly anchor the POSS component to the substrate forming mechanically and chemically stable coatings.These coatings engineered are superrepellent to water–ethanol solutions and afford enhanced load capacity when combined with mesh substrates,promising for drag reduction and anti-fouling applications in marine explorations.Chapter Four further optimizes the construction of superrepellent surfaces using a cyanoacrylate binder and a fluorinated silane as the low-energy component instead of POSS.The engineered coatings possess hierarchical textures with multi-reentrant curvatures,displaying strong repellence even to ultralow surface tension liquids as well as versatile tunability of wettability using stretchable substrates.The hierarchical structure together with the low-energy of fluorinated surface chemistry significantly reduces the solid –liquid interactions,serving as a possible strategy for anti-icing applications as well as a desirable platform for manipulating droplets and studying their behaviors.Chapter Five studies the collision and bouncing behavior of droplets occurring on the superrepellent surfaces as engineered in Chapter Four.The collision results(bouncing,coalescence,and stretch separation)have been experimentally studied together with theoretical predictions and found that coalescence efficiency is strongly correlated with the polarity of collision droplets.Furthermore,the head-on bouncing collisions between liquid droplets are proved similar to the scenario when liquids impact on superrepellent surfaces,as the contact time follows the same scaling law.However,the off-center bouncing collisions result in much-reduced contact time as the collision becomes more off-center.A concept of effective collision has been proposed and experimentally verified to evaluate the contact time of off-center collisions,therefore contributing to the family of theoretical predictions in the field of droplet bouncing.This dissertation,focusing on the key scientific questions surrounding surface fouling,includes four research chapters studying the pathways in the engineering of heterogeneous or homogeneous superrepellent coatings and the roles of hierarchical structures.The research on the interactions between surfaces and liquids reveals that surface wettability is strongly correlated with surface chemistry and microstructures.These findings,therefore,are fundamental for the development of next-generation advanced interfacial materials.