Emulsion rheology and properties of polymerized high internal phase emulsions
High internal phase emulsions are highly concentrated emulsion systems consisting of a large volume of dispersed phase above 0.74. The rheological properties of high internal phase water-in-oil emulsions were measured conducting steady shear, oscillatory shear and creep/recovery experiments. It was found that the yield stress is inversely proportional to the drop size with the exponent of values between 1 and 2. Since the oil phase contains monomeric species, microcellular foams can easily be prepared from high internal phase emulsions. In this study, the microcellular foams combining a couple of thickeners into the conventional formulation of styrene and water system were investigated to understand the effect of viscosity ratio on cell size. Cell size variation on thickener concentration could be explained by a dimensional analysis between the capillary number and the viscosity ratio. Compression properties of foam are important end use properties in many practical applications. Crush strength and Young's modulus of microcellular foams polymerized from high internal phase emulsions were measured and compared from compression tests. Of the foams tested in this study, the foam prepared from the organoclay having reactive group as an oil phase thickener showed outstanding compression properties.
Organic-inorganic networks in foams from high internal phase emulsion polymerizations
Hybrid foams, which combine an inorganic polysilsesquioxane network with an organic polystyrene network, were successfully synthesized using high internal phase emulsions (HIPE). Methacryloxypropyltrimethoxysilane (MPS) was copolymerized radically with styrene (S) and divinylbenzene (DVB) in the organic phase of the emulsion. The hydrolytic condensation of the trimethoxysilyl groups formed an inorganic polysilsesquioxane network, which significantly increased the high temperature modulus and thermal stability of the foam. The hybrid foam had an open-cell structure typical of polymer foams based on HIPE (polyHIPE), with a significantly smaller cell diameter than S/DVB polyHIPEs. In the absence of DVB, there is no crosslinked network to restrict the mobility of MPS and the polysilsesquioxane network is more fully developed. At low MPS contents, the thermal stability of the foams is higher for foams with DVB, reflecting their higher crosslinking density. At high MPS contents, the thermal stability is higher for foams without DVB, reflecting the more fully developed inorganic network.
The Game Planners: Transforming Canada's Sport System.
The Game Planners studies the policy-making process in six Canadian national sports organizations, each of which deals with a different high-profile Olympic event. The authors argue that the creation of a "high-performance" sport system in Canada is due to pressure from three areas: the Canadian government, the physical education profession, and the sports community.