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Mawson Lakes, Australia

Chen S.A.,University of Melbourne | Chen S.A.,IBM | Clasohm L.Y.,Ian Wark Research Institute | Horn R.G.,Deakin University | Carnie S.L.,University of Melbourne
Langmuir | Year: 2015

An aspect of dynamic colloidal interactions that has received little attention is the osmotic stress associated with nonequilibrium distribution of solutes. Recent experiments on a mercury drop near a mica surface show a dimple forming on the mercury/water interface when there is a sudden change in the electric potential of the mercury drop coated with a self-assembled monolayer (SAM) of 11-mercapto-1-undecanoic acid thiol molecules. A reasonable hypothesis is that the dimple formation is due to the desorption of a fraction of the SAM from the mercury drop surface when the surface potential is changed. The osmotic pressure in the thin film region increases as a result of the presence of the thiol molecules in the region, giving rise to the observed dimple. A model including the effects of osmotic flow, disjoining pressure, interfacial tension and hydrodynamic pressure is developed to test the hypothesis. The simplest version of the model, in which desorption is uniform and instantaneous, can produce a dimple whose growth is significantly more rapid than its decay, in qualitative agreement with the data. However, quantitative agreement is lacking. Several refinements to the model, including effects such as the change in interfacial tension as thiols are desorbed, gradual thiol desorption, a change in disjoining pressure as charged thiols are desorbed and nonuniform desorption do not change the qualitative picture. The qualitative success of the model suggests the osmotic pressure mechanism is correct, but the detailed picture of the SAM desorption at positive mercury surface potentials is not sufficiently well understood. The model reveals that the osmotic dimple is not the time-reverse equivalent of the usual hydrodynamic dimple phenomenon. We suggest that transient deformation of thin films by osmotic flow is a new and little-studied mechanism influencing the structure of stable thin films and the interaction of deformable drops. This has implications for colloidal interactions in a broader range of systems where solute concentration may not be homogeneous, for example in solute transfer processes. © 2015 American Chemical Society.

Du J.,e Applied Center for Structural and Synchrotron Studies | Du J.,University of South Australia | Morris G.,Victoria University of Melbourne | Pushkarova R.A.,Ian Wark Research Institute | St. C. Smart R.,e Applied Center for Structural and Synchrotron Studies
Langmuir | Year: 2010

The flocculation and solid/liquid separation of four well-characterized kaolinites (2 well, 2 poorly crystallized) have been studied for comparison of surface structure (SEM), aggregate structure during flocculation (cryo-SEM), settling rate, and bed density (with raking). It is shown that major differences in these properties are largely due to crystallinity and consequent surface structure of the extensive (larger dimension "basal") face. Well-crystallized kaolinites, with higher Hinckley indices and lower aspect ratios, have relatively smooth, flat basal surfaces and thicker edge planes promoting both effective initial bridging flocculation (largely edge-edge) and structural rearrangement to face-face during the raking process. This results in faster settling rates and more compact bed structures. Poorly crystallized kaolinites, with low Hinckley indices and high aspect ratios, exhibit ragged, stepped structures of the extensive face with a high proportion of nanosized islands forming cascade-like steps (i.e., multiple edges) contributing up to 30% of the specific surface area and providing flocculant adsorption sites (hydroxyl groups) across this extensive face. This leads to bridging flocculation taking place on both edge and extensive ("basal") planes, producing low-density edge-face structures during flocculation which leads to slow settling rates and poor bed densities. In particular, the complex surface morphology of the poorly crystallized kaolinites resists the transformation of edge-face structures to dense face-face structures under shear force introduced by raking. This results in low sediment density for poorly crystallized kaolinites. The studies suggest that the main influence on settling rates and bed densities of kaolinites in mineral tailings is likely to be related to the crystallinity and surface morphology of the kaolinite. They also suggest that interpretation of kaolinite behavior based on models of a flat (001) basal plane and edge sites only at the particle boundaries is not likely to be adequate for many real, less-crystallized kaolinites. © 2010 American Chemical Society.

Chandrasekaran S.,Mawson Institute | Macdonald T.J.,Ian Wark Research Institute | Gerson A.R.,Mawson Institute | Gerson A.R.,University of South Australia | And 2 more authors.
ACS Applied Materials and Interfaces | Year: 2015

An effective solar-powered silicon device for hydrogen production from water splitting is a priority in light of diminishing fossil fuel vectors. There is increasing demand for nanostructuring in silicon to improve its antireflective properties for efficient solar energy conversion. Diatom frustules are naturally occurring biosilica nanostructures formed by biomineralizing microalgae. Here, we demonstrate magnesiothermic conversion of boron-doped silica diatom frustules from Aulacoseira sp. into nanostructured silicon with retention of the original shape. Hydrogen production was achieved for boron-doped silicon diatom frustules coated with indium phosphide nanocrystal layers and an iron sulfur carbonyl electrocatalyst. © 2015 American Chemical Society.

Yu Y.,Ian Wark Research Institute | Addai-Mensah J.,Ian Wark Research Institute | Losic D.,Ian Wark Research Institute
ICONN 2010 - Proceedings of the 2010 International Conference on Nanoscience and Nanotechnology | Year: 2010

Three-dimensional (3-d) gold microstructures with complex architecture were prepared from silica-based diatom microshells (frustules) using template synthetic process based on the electroless metal (gold) deposition. Diatom frustules were replicated into gold microstructures with a high-precision, entirely preserving their shape and micro and nanoscale porous features. © 2010 IEEE.

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