Driving Forces for Wetting and Adsorption on Functional Surfaces

Abstract

Functional surfaces coated with nano-thin films have potential applications in many areas. In this Thesis, liquid spreading and adsorption onto surfaces were studied as a function of surface properties, such as chemical composition, roughness and functionality. In the first study, the spontaneous motion of water droplets onto wedges surfaces was studied after placing them at the narrow end of a wedge. The actuation force applied on the droplets at the tip of the wedge overcomes the adhesion forces due to the friction forces and contact-line pinning. The velocity of the moving droplets depends on the geometry of the wedge: droplets moved at significantly higher velocity on wedges with curved edges (69 mm/s) than on wedges with straight edges (36 mm/s). A mathematical model successfully described the motion of the droplets on the developed wedges. In the second study, structured surfaces were designed that entirely repel oil droplets underwater. Poly(4-vinylpyridene) (P4VP) surfaces with wrinkled nano and micro-topography were developed to trap a water layer within the surface texture by capillary forces. Surfaces with double-scale roughness were more robust in maintaining the water layer under the oil droplets. Oil droplets rolled off the wrinkled P4VP surfaces when tilted at a very low angle (4°) underwater. The developed surfaces were as transparent as glass when they were infused with water. Finally, surfaces functionalised with supramolecular structures were used to enhance the adsorption of guest molecules from solution. Surface-immobilised monolayers of the macromolecule Blue Box (BB) were used to remove the toxic catechol and 4-ethylcatechol molecules present in industrial wastewater. The nanofilm of BB on SiOx surfaces catalysed the polymerisation leading to the formation of agglomerates of catechol polymers on the surface. This interaction resulted in the adsorption of up to 10,000 guest molecules per 1 host molecule, instead of the expected 1:1 ratio.