Miniemulsions: droplet size and stability versus final particle size

In this work, the effect of the sonification time on the stability of styrene and styrene/butyl acrylate (50/50) miniemulsions was investigated by centrifugation. Octadecyl methacrylate (ODMA) miniemulsion was used as a comparative system owing to its degradation by monomer diffusion being minimum. The droplet and particle size distributions were also evaluated by capillary hydrodynamic fractionation (CHDF) and dynamic light scattering (DLS) for the various sonification times. For the styrene/butyl acrylate miniemulsions, the most stable were those formed with the shortest sonification times tested, 1 and 2 min. For the styrene miniemulsions, longer sonification times were required than for the styrene/butyl acrylate miniemulsions and the most stable sample was formed by the use of 4 min of sonification. It was observed that larger droplets (300 to 1000 nm) were formed at shorter sonification times, although the numbers of these were reduced significantly after polymerization owing to monomer diffusion from these larger “reservoir” droplets to the smaller droplets and particles.