Aqueous dispersions of silica shell/water-core microcapsules.
The preparation is described of water-core/silica-based shell particles, from W/O emulsion droplets, by adding alkoxysilanes to the oil-continuous phase, to form the shell by an interfacial condensation reaction at the W/O interface. In order to form relatively thick (and hence stronger) shells, it is found necessary to use a mixture of tetraethoxysilane (TEOS) and diethoxydimethylsilane (DEODMS), rather than TEOS alone. It is suggested that, in the former case, trans-shell diffusion of the alkoxysilane monomers (from the oil side) and water molecules (from the aqueous side) can continue, as a result of the higher permeability of the shells to these small molecules, thus allowing the interfacial condensation reaction to continue, even when the reaction would have ceased for a harder shell, having a much lower permeability, as occurs when TEOS alone is used. A successful method of transferring the water-core/silica-based shell particles from oil into water is described, based on the direct centrifugation of the particles from an upper oil phase (containing the dispersed particles initially) into a lower aqueous phase placed beneath, which contains a surfactant capable of adsorbing onto the particles and making them water-wetted.
O'Sullivan
Michael
M
School of Chemistry, University of Bristol, Bristol BS8 1TS, UK.
Vincent
Brian
B