School of Chemistry - Theses
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ItemSurface engineering for mechanically robust superhydrophobic films( 2016)The inherent surface roughness of superhydrophobic surfaces renders them mechanically fragile and limits their use in many applications from self-cleaning to anti-fouling. With the view of improving the mechanical durability of these films several steps have been taken to both identify and understand the underlying principles for the apparent dichotomy between superhydrophobicity and mechanical durability. Rough surface coatings with variable surface roughness have been developed and examined using atomic force and electron microscopy, contact angle goniometry nanoindentation as well as industry based mechanical testing. Prepared predominately by bottom up strategies such as sol-gel processing, a diverse variety of superhydrophobic surfaces were prepared exhibiting contact angles greater than 150° and sliding angles less than 10°. Subsequently, several synthetic protocols have been developed to overcome these difficulties. Within conventional sol-gel derived coatings, by normalizing against the surface topology, the enhancement in abrasion resistance can be correlated to crosslinked polymer material property ratios H/E and H3/E2, providing a rationale for polymer choice to wear improve wear behavior in future coatings. Understanding of geometric limitations led to the development of polymer spheres prepared through emulsion synthesis which were utilized as sacrificial templates within a siloxane matrix to yield films with crater-like surface roughness. Surface roughness was controlled through the template geometry and concentration. The intrinsic hydrophobicity of the MTMS matrix provides enhanced longevity towards wear. This was subsequently improved through the development of polyhedral silsequioxane chemistry. Further design of the crater-like surface was inspired by mimicking the fascinating assembly of particles in natural materials. Hierarchical assembly of anisotropic particles to achieve mutually exclusive properties inspired work toward the preparation of biomimetic, superhydrophobic coatings predominantly from the incorporation of silica and polyaniline fibers and rods into craterlike surfaces.
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ItemSynthesis and self-assembly of core-shell gold nanorod-PNIPAM nanoparticles( 2016)An essential requirement for the use of nanoparticles in self assembly applications is ensuring their colloidal stability is maintained, as well as being able to tailor their properties for enhanced functionality. One way of doing so is through the incorporation of nanoparticles in responsive microgels, leading to the formation of inorganic/organic hybrid nanocomposites. The aim of this research was to develop a generic protocol for the preparation of hybrid core-shell microgels composed of nanoparticle cores and responsive polymer shells. Specifically, core-shell gold nanorod - poly-N-isopropylacrylamide (PNIPAM) particles with high yield and monodispersity were synthesised. Due to the high sensitivity of the longitudi-nal plasmon band to its local environment, the change in refractive index caused by the temperature-induced collapse of the PNIPAM shell led to a red-shift on the order of tens of nanometres in the plasmon band. This shift was reversible for multiple heating/cooling cycles, and no aggregation of the gold nanorod cores was observed. Concentrating the gold nanorod-PNIPAM solutions at high volume fractions enabled them to crystallise, thereby exhibiting strong diffraction peaks. The formed colloidal crystals could be melted upon annealing, and re-formed upon cooling due to the responsive behaviour of the PNIPAM shell. These crystals exhibited fascinating optical behaviour which opens a pathway to a new class of hybrid materials with potential use in a wide array of applications.