Composite Coatings for Liquid Repellency: From Formulations to Applications

Wetting phenomena is observable in everyday commercial products and has been studied extensively for centuries. Extreme wetting phenomena (super repellency or super wettability), however, has come to light in the past decade and researchers have explored countless ways of making artificial surfaces that mimic the behavior of several naturally-occurring, extreme-wettability surfaces, such as the Lotus leaf, rose petal, butterfly wings, etc. Many works have looked into explaining the fundamental nature or behavior of these surfaces, and what liquid management problems these surfaces offer potential solutions to. In general, man-made liquid-repellent surfaces are created by artificially modulating the surface chemistry and surface roughness of a substrate (low surface energy and multi-scale surface roughness) through a variety of techniques, such as laser-ablation, chemical etching, ultraviolet radiation (UV) treatment, chemical functionalization, or coating processes. Regardless of how these extreme-wettability surfaces are made, they have a unique ability to solve engineering problems (e.g. drag reduction, promoting corrosion resistance, enhancing condensation, etc.) in ways that are not possible by using traditional methods. Additionally, researchers have found ways of making man-made surfaces that feature spatially-patterned regions of varying wettability (a.k.a. wettability-patterned surfaces) to aid in solving even more complex engineering problems, such as microfluidic tasks and point-of-care (POC) diagnostics. The focus of this dissertation is to present simple ways of making composite coatings from various materials to demonstrate repellency to a variety of liquids. Material selection and processing methods for several coating formulations are presented along with their potential for solving real-world engineering problems. Various experimental techniques (e.g. contact angle measurements, physicochemical methods) are used to characterize each of the coatings and to explain the underlying working mechanisms of each material system. This research offers insight into fundamental aspects of extreme surface wettability, and guidance on how to tailor a material system through appropriate material selection and processing techniques best suited for a variety of liquid handling applications.