Crick, C.R.; (2011) The chemistry and CVD of hydrophobic surfaces. Doctoral thesis , UCL (University College London).

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Abstract

This thesis details the use of chemical vapour deposition (CVD) to deposit hydrophobic surfaces, in addition to this, the functional properties are investigated and further characterisation of the surfaces extreme water repulsion (superhydrophobicity) is made. The design and manufacture of surfaces that repel water (hydrophobic) draws much inspiration from the natural world, including examples of superhydrophobic leaves. The way water can interact with a surface is characterised, with many examples of superhydrophobic surface generation provided from the literature, along with general routes toward their formation. The main aspects of CVD depositions are addressed and examples of hydrophobic surfaces using this technique are cited. The novel deposition of thermosetting and thermosoftening polymers has been investigated, with the role of the CVD deposition mechanism emphasised. The deposition of the polymer occurs via the preformation of polymer particles, which is not typical in CVD, these were then deposited onto the substrate. The result was an easy-to-produce and robust superhydrophobic thin film, constructed from an inherently hydrophobic material. The same principle is then expanded to silica microparticles, films of the particles were deposited on to a substrate with hydrophilic surfaces originally deposited. The silica films were subsequently rendered exceptionally superhydrophobic by a simple post-treatment. The formation of copper films is then reported, using copper nitrate precursors a relatively flat metallic copper film was formed. The films were then roughened by reaction to form copper hydroxide nano-crystals, this hydrophilic surface is again functionalised to render it superhydrophobic. All films deposited were characterised using energy dispersive X-ray analysis, glancing angle X-ray diffraction, UV/Vis spectroscopy, infra-red/Raman spectroscopy and scanning electron and atomic force microscopy were used to study surface morphology, with the hydrophobicities of each surface quantified. The superhydrophobic elastomer films underwent microbiological testing in order to examine the adhesion of bacteria. A substantial reduction in the ability of bacteria to attach to the superhydrophobic surfaces was observed and rationalised through a reduction in available contact between the media of the bacteria (water) and the surface material. The dynamic interaction between water and surfaces was examined through water bouncing. The dependence of water bouncing on surface hydrophobicity and microstructure was studied, in addition to the effect of water droplet volume and impact velocity. A new definition and scale for superhydrophobicity is proposed, through the ability of water droplets to bounce on a surface. Finally the insight gained from previous work carried out is used in developing a device for separating mixtures of oil and water, through the use of superhydrophobic meshes.

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