Surface wettability control by vapor-deposited nanocoatings for water harvesting

Engineering the surface wettability of water harvesting devices is critical to improving water harvesting performance. This dissertation presents five research projects. First, vapor-deposited fluorinated polymer nanocoatings were developed to improve membrane surface hydrophobicity. The coated membranes showed salt rejection rates of >99.99% in membrane distillation (MD) of saltwater, in contrast to the uncoated membranes failing to reject salts. Besides, the coated membranes exhibited 48.0–73.0% improvement in water flux as the membrane pores increased from the conventional small size of 0.2 μm to the large size of 2.0 μm. Second, Janus membranes with hydrophilic and hydrophobic nanocoatings on each side were developed for MD desalination of oil-contaminated saltwater. The solvent-free nature of the coating deposition circumvented the challenge of interfacial incompatibility between the hydrophilic and hydrophobic layers. Third, a method for hydrophilic modification of microfiltration membranes was developed using vapor-deposited silica nanocoatings, which enabled efficient removal of oil contaminants in the microfiltration of emulsified wastewater, as well as the improved membrane anti-fouling performance against humic substances and bovine serum albumin proteins. Fourth, a novel surface wettability patterning method was developed based on ultraviolet-assisted vapor deposition of hydrophilic poly(4-vinyl pyridine) polymers onto hydrophobic primers. This patterning method can be applied to nearly any substrate without the restriction by substrate chemical composition or physical morphology, addressing the challenge that most existing methods are limited to certain substrates. The wettability patterned surfaces demonstrated significantly higher efficiency than homogeneously wetting surfaces in collecting water from moisture air. Fifth, a new strategy to separate oil-water microdroplets using wettability-patterned surfaces was developed, and its application for the rapid detection of cholesterol in aqueous samples was demonstrated.