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The understanding of mechanical properties of thin films at the nano/sub micron level is important for rational selection of coatings for critical applications. In this thesis, the nanomechanical properties of plasma polymerised thin films were investigated in detail. The principal aim of the present work is to gain a fundamental understanding of the nanomechanical properties of plasma polymerised siloxane thin films, and the influence of the substrate on those properties. / Thesis (MApSc(MineralsandMaterials)--University of South Australia, 2006

The surface force apparatus (SFA) has been an important technique for making direct force measurements and has contributed enormously to our understanding of colloidal interactions. The conventional SFA has been limited to measuring forces between solid surfaces, until recently when a modified SFA was developed at the Ian Wark Research Institute [1]. A fluid drop (mercury) is introduced into the apparatus which allows a range of deformable surfaces to be studied in the SFA. This project is an extension of this technique. Interactions between a mica sheet and a mercury drop are studied, including the modification of mercury with self-assembled monolayers (SAMs) of thiol surfactants, and the drop deformation due to non-equilibrium adsorption effects and hydrodynamic forces. / SAMs can form spontaneously onto a surface by immersing the substrate into an appropriate surfactant solution. They have been used, generally formed on gold surfaces, for biosensors, chemical sensors, micro-electronics and detection of DNA and protein adsorption. In our study, mercury was chosen as the substrate, for its defect-free, renewable and molecularly smooth surface. The additional advantage of being an ideal polarisable electrode allows a potential to be applied to the mercury, and hence control of the surface forces. The charging behaviour of the mercury is changed by introducing a SAM onto the surface. An uncharged SAM (11-mercapto-1-undecanol or 11-mercaptoundecane) modifies the dipole potential of the mercury by replacing the water molecules oriented on the surface, whereas a charge SAM (11-mecapto-1-undecanoic acid) brings additional charges to the surface. / Drop deformation is an important factor when deformable surfaces are involved in colloidal systems, e.g. emulsions, foams, in mineral flotation and in biological systems. Drop profiles of a mercury surface which is already close ( ̃50 nm) to a flat mica sheet, with or without a SAM, were measured using the SFA technique. For the SAM-modified mercury, the negatively charged functional group (-COO⁻) yields a repulsion against mica, and a thin film is formed between the surfaces. When the applied potential was scanned negatively, desorption of thiols occurred at certain potentials, increasing the local solute concentration in the solution. The restricted flow of the solute within the small gap creates an excess osmotic pressure in the thin film compared to the bulk solution. As a result, the film pressure exceeds the internal pressure of the drop, inverting the drop curvature and forming a dimple. We propose that the drainage of the dimple is a diffusion-controlled process, which is supported by the comparison of the data with a simple model calculation. / For the bare mercury drop, a negative potential was applied to the mercury to provide a repulsion to form a thin film. Mica was then driven towards the mercury with an abrupt step. Beyond certain step sizes, a rippled shape - which we dub a “wimple” - was observed before it evolved into a classical hydrodynamic dimple. At small step sizes, no wimple was observed, but curiously the film in the central part thickens before eventually thinning out. This shows that fluid first flows towards the central axis before reversing its flow direction and flowing radially outwards. / Thesis ([PhDApSc(MineralsandMaterials)])--University of South Australia, 2005.

The wettability of materials is important in many natural and industrial processes. In this thesis, the wettability of chemically heterogeneous surfaces was investigated with respect to the size, shape and orientation of individual defects. Heterogeneous surfaces were structured by photolithography, using self-assembled monolayers (SAMs) of diverse functionality and, thus, wettability. In order to maximise any possible departure from theory, the wettability of the high-and low-energy regions of these heterogenous surfaces was chosen to differ substantially. The purity of the defects was optimized by studying the SAM formation and the patterning processes, whilst the influence of roughness was minimized. The focus of this work is therefore on chemical heterogeneity. The Wilhelmy plate method was employed to ascertain the wetting behaviour of individual high- and low-energy defects. Simultaneous measurement of the capillary force and the plate position allowed full characterization of the wettability at the defect boundaries. In addition, integration of the Wilhelmy trace enabled the work associated with advancing or receding a liquid over these defects to be quantified. / The defect boundary orientation was of critical importance to the wetting behaviour. Wetting boundaries perpendicular to the liquid front did not result in any deviation from theoretical predictions. Wetting boundaries that were arranged parallel to the liquid front, however, caused contact line pinning which, in turn, caused contact angle hysteresis. Therefore these boundaries are directly responsible for the departure from wetting theory for heterogeneous surfaces (i.e. the Cassie Equation). These observations are consistent with earlier studies of wetting hysteresis by Johnson and Dettre (1964) and Neumann and Good (1972). Extending their work, this thesis examined the extent of wetting hysteresis at individual rectangular defects with respect to the defect dimensions. The nature of wetting hysteresis was studied quantitatively and, as a result, a simple model for hysteresis was proposed. This model predicts that, for a high-energy defect, the work associated with an advancing liquid will always be less than the theoretical value due to capillary rise within the effect. However, the work associated with a receding liquid will be equal to the theoretical prediction (the opposite is true for low-energy defects). The proposed model was validated for two different liquids (water and ethylene glycol) rectangular and circular defects of macroscopic dimensions. For these surfaces, the empirical data and the proposed model showed excellent agreement for both high- and low-energy defects. This agreement is strong evidence that high- and low-energy defects induce distinctly different wetting behaviour on heterogeneous surfaces. / The proposed model for hysteresis was qualitatively applied to heterogeneous surfaces containing micro- and nanoscopic defects. For micropatterns of high- and low-energy defects, of identical composition, the wettability was entirely different. High-energy defects induced a deviation from theory for only the advancing contact angles, whilst low-energy defects only influenced the receding angles. These observations were qualitatively consistent with the outcomes predicted by the proposed model for hysteresis. For nanoscopic defects, however, the advancing contact angles were consistent with Cassie's law within reasonable error. The derivation of Cassie's equation assumes that there is no capillary rise within the chemical defects. The capillary rise within a nanoscopic defect must be extremely small, according to extrapolation of measurements performed on macro and microscopic defects. Therefore, consistency between the wettability of nanoscopic defects and Cassie equation predictions might be expected. The hysteresis mechanism outlined within this thesis can be quantitatively applied to macroscopic defects, whereas its application to micro and nanoscopic defects is qualitative. / Finally, several applications of this fundamental research, which are directly related to real systems, have been outlined. These include mineral flotation, oil recovery, liquid movement, directed crystallization, Secondary Ion Mass Spectrometry for flotation analysis and patterning of inorganic surfaces. / Thesis (PhDApSc(MineralsandMaterials))--University of South Australia, 2004.

Thesis (PhD)--University of South Australia, 2004.

Thesis (PhD)--University of South Australia, 2003.

Thesis (PhD) -- University of South Australia, 1994

Thesis (PhD)--University of South Australia, 1999

Thesis (Master of App. Sci. in Chem. Tech.) --University of South Australia, 1991.

The structure of the oxide/aqueous electrolyte interface has been studied. The surface porosity of several oxides to ions is evaluated and the contribution of such porosity to the double layer properties determined by surface charge measurements. The oxides studied are B.D.H. precipitated silica, before and after heat treatment, rutile, goethite, hematite and amorphous ferric oxide. The surface porosity was evaluated using nitrogen adsorption for physical porosity, tritium exchange for surface hydration and dissolution for surface crystallinity. It is found that the surfaces of metal oxides may be divided into two categories; those that are porous to ions and those that are non-porous. Of those studied only the precipitated silica and the amorphous ferric oxide are porous. The porosity is probably due to an easily permeated layer of hydrolysed oxidic material. It does lead to exceptionally high surface charges. However the non-porous oxides also exhibit high surface charges so that while surface porosity may, in some cases, contribute to oxide double layer properties, it cannot be a general explanation of the high differential capacities observed. A site-binding model for non-porous oxide/aqueous electrolyte interfaces is introduced, in which it is proposed that the adsorbed counter ions form interfacial ion pairs with discrete charged surface groups. This model is used to calculate theoretical surface charge densities and potentials at the Outer Helmholtz Plane. The calculated values are consistent with experimental data for oxides provided a high value of the inner zone capacity is accepted. An explanation is provided for the difference between silica and most other oxides in terms of the dissociation constants of the surface groups.