Surface Chemistry at High Ionic Strength

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Associate Professor Vincent S. J. Craig
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The aim of this study is to understand the behavior of mineral particles in concentrated electrolyte solutions using surface force techniques. To this end there are two significant challenges.

1) The first challenge relates to the type of surface forces that dominate at high electrolyte concentration. They are very short in range and poorly understood theoretically, but it is known that they are related to the solvation of the surface layer of a material or ions adsorbed to that layer, hence they are called solvation or in aqueous solutions hydration forces.

2) The second challenge is to prepare surfaces that are suitable for investigation by surface force measurement techniques and is intimately related to the first challenge as the very short range over which hydration forces operate requires that surface roughness is controlled at a level comparable to or less than the range of the hydration forces.

Therefore much effort has concentrated on acquiring or producing suitable surfaces for investigation. With silica surfaces this has not posed any significant challenge but other surfaces have not met with success. To this end we have purchased an Atomic Layer Deposition system that will enable us to deposit materials that mimic the mineral surface of interest onto silica surfaces. This instrument has now arrived and been installed in our laboratory. However there have been considerable delays in the arrival of the precursor chemicals, therefore we have not been able to use the instrument for the preparation of mineral like surfaces to date. These chemicals have now just arrived and we can now proceed. We have continued to develop the photon pressure technique but we do not present any new data relevant to this study here as measurements using the photon pressure technique require ultra-smooth surfaces and we have already presented data on silica surfaces the only surfaces that have been sufficiently smooth for this use up to this time. These surfaces will now be available to us with the arrival of the precursor chemicals for the ALD system.