David Henry, Postdoctoral Fellow in Applied Physics at RMIT University, Victoria, Australia, will present the following seminar from the Pacific Rim Conference in Nanoscience (7-11 September 2004). The seminar will be available for viewing and discussion through the Nanotech Hub at http://nanotech.colayer.net/ both during the conference and after the conference.
Theoretical Nanoscale Design of Self-Cleaning Surfaces
In the last few years there has been a considerable amount of work on the development of contamination resistant coatings. One approach is based on the ‘lotus effect' which is observed in nature. Leaves of lotus plants are known to stay clean even in dirty environments and it is now clear that this cleanliness is caused by the extreme non-wetting character of the leaves, with water contact angles greater than 150º. This super-non-wetting character is a result of the leaf surface being covered by a layer of low surface energy wax that is extremely rough on a nano-scale. One of the difficulties involved in using this effect in a synthetic system is that the low surface energy, rough surfaces are easily damaged and can be contaminated by higher surface energy organic contaminants. The lotus plant solves this problem by continually exuding wax to the surface, but this may be difficult to reproduce in a synthetic system. An alternative approach is to produce a strongly hydrophilic surface for which hydrophobic contaminants have little or no affinity and where water would easily remove any contaminants coming in contact with the surface.
We are involved in the nano-scale design and modification of organic coating surfaces for contamination resistance using theoretical techniques. Simulations are performed to gain a better understanding of the nature of the interaction between carbonaceous contaminants and polymer surfaces. The figure illustrates a fully atomistic model of an interface between a polymer surface and graphite which approximates common carbonaceous contaminants. Using classical potentials we calculate the adhesion energy as a function of interfacial separation (shown) for such interfaces with varying polymer surface composition. With this knowledge we are then able to propose surface modifications that will lead to reduced adhesion of contaminants prior to costly experimental testing.