Preparation of uniform-sized polystyrene-polyacrylamide composite microspheres from a W/O/W emulsion by membrane emulsification technique and subsequent suspension polymerization

Uniform-sized polystyrene/polyacrylamide (PST-PAAm) composite microspheres were prepared from a water/oil/water (W/O/W) emulsion by using a glass membrane emulsification technique. An AAm aqueous solution was emulsified into an oil phase containing ST initiator, Span 85, and PST by ultrasonification to obtain W/O primary emulsion. Then, the W/O emulsion was pressed through the uniform pores (5.25 mum) of a SPG (Shirasu porous glass) membrane into an outer aqueous solution to form uniform-sized W/O/W emulsion. PST was added to increase the viscosity of oil phase, retarding the phase separation between inner water phase and oil phase during the membrane emulsification process. After the W/O/W emulsion was polymerized, the uniform-sized composite particles around 20 mum were obtained. It was found that the spherical PAAm microdomains were distributed inside and on the surface of a composite particle; the number of PAAm domains on the surface was controllable by varying cross-linking density of the PST phase.