Kalmoni, Julie Jalila; (2024) Surface Modification of Superhydrophobic Materials. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

This thesis explores the fabrication of fluorine-free superhydrophobic materials and their resultant surface modification with metal oxides via vapour phase deposition techniques, specifically aerosol-assisted chemical vapour deposition (AACVD) and atomic layer deposition (ALD). Initially, superhydrophobic materials were produced without the use of fluoroalkylsilanes, which are fluorine-based chemicals needed to lower the surface energy of the materials. Low surface energy reagents are a requirement of superhydrophobic coatings. As an alternative, two of the most prevalent fatty acids were used instead. In addition to this, SiO₂ nanoparticles (needed to impart roughness), polydimethylsiloxane and ethyl acetate were used for the one-pot synthesis of this mixture, deposited via AACVD. To optimise the superhydrophobicity of these films, investigations into influential parameters such as temperature, concentration and time were comprehensively trialled. The next study involved the deposition of TiO₂ via the titanium(IV) isopropoxide (TTIP) precursor by AACVD, as an additional layer on top of the superhydrophobic film. A range of concentrations and loadings were trialled to determine how the surfaces’ properties and durability of the superhydrophobic films would change, potentially producing a photocatalytic self-cleaning film. Photocatalytic testing confirmed the improved photocatalytic properties of the films with the superhydrophobic underlayer. Hence the surface properties, morphology and overall durability were studied. The optimum conditions for the synthesis of fluorine-free superhydrophobic films were selected for the next study involving the deposition of TiO₂ via the ALD of tetrakis(dimethylamido)titanium(IV). Visual inspection and X-ray photoelectron spectroscopy indicated a more uniform deposition of TiO₂ on the superhydrophobic films. Various cycle numbers and temperatures were investigated. The final study involved depositing CeO₂ by AACVD onto the superhydrophobic films by using a lab-synthesised cerium dibenzoylmethane precursor. Again, the surface was studied and characterised. Unfortunately, the films showed reduced self-cleaning properties, poor thermal stability and relatively low water contact angles.

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