Speaker: Mr Ahmed Owais Mohamed Ahmed, School of Chemistry, The University of Sydney (Refreshments to follow this seminar)

Host: A/Prof Chiara Neto [Map]

Abstract:

Functional surfaces coated with nano-thin films have potential applications in many areas. In this Thesis, the processes of 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 surfaces was studied after placing them at the narrow end of a triangular wedge. The droplets spontaneously move towards the wide end of the wedge due to the Laplace pressure difference between the front and the back of the droplet. 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 nano and wrinkled 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 wrinkled P4VP 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, carcinogenic and mutagenic catechol and 4-ethylcatechol molecules present in industrial wastewater. The nanofilm of BB on SiO surfaces catalysed the oxidation polymerisation leading to the formation of agglomerates of catechol polymers on the surface. The catechol polymers formed at a much higher rate in the presence of the immobilised BB molecules. This interaction resulted in the adsorption of up to 10,000 guest molecules per 1 host molecule, instead of the expected 1:1 ratio.