Effect of Ostwald ripening on styrene miniemulsion stabilized by reactive cosurfactants

The Ostwald ripening rate data were determined by photon correlation spectroscopy for styrene miniemulsions stabilized by various cosurfactants such as dodecyl methacrylate (DMA), stearyl methacrylate (SMA), cetyl alcohol (CA) or hexadecane (HD) to retard diffusion of styrene (ST) from small droplets to large ones. The reagent DMA or SMA contains a methacrylate group and, therefore, can be used as a reactive cosurfactant in subsequent ST miniemulsion polymerization. The effectiveness of these cosurfactants is strongly dependent on their solubilities in water. The higher the solubilty of cosurfactant in water, the greater the extent of Ostwald ripening occurring in the miniemulsion. The water solubility data of these cosurfactants are not available in the literature, except HD. Based on a procedure established in this work, the solubilities of these cosurfactants in water can be estimated by Lifshitz-Slyozov-Wagner (LSW) theory. The solubility of cosurfactant in water in the decreasing order is: CA(5.77 x 10(-8)) > DMA(1.38 x 10(-8)) > SMA(3.23 x 10(-9)) > HD (1.14 x 10(-9) ml/ml). In addition, the LSW theory can be used to calculate the monomer droplet-water interfacial tension. This feature may provide useful information on the degree of droplet surface coverage by surfactant. (C) 1998 Elsevier Science B.V.