Magnetite (Fe3O4) microcapsules prepared using a glass membrane and solvent removal

Fine magnetite powders dispersed in polymer solution were encapsulated from an oil-in-water emulsion prepared by an emulsification process employing a porous glass membrane and subsequent evaporation of the solvent. Styrene-b ased copolymers were dissolved in a magnetic fluid, and then continuously p ushed through the pores of glass membrane into the aqueous phase, which had dissolved polyvinyl alcohol (PVA) and sodium dodecyl sulphate (SDS) as a m ixed stabilizer. P(styrene-co-acrylic acid) (PS-AA), P( stryrene-co-butyl a crylate) (PS-BA) and styrene-butadiene rubber (SBR) were dissolved in the s pecially ordered magnetite fluid (25 wt% magnetite dispersed in toluene) se parately or as a mixture, and uniform droplets suspending the magnetic part icles were obtained. After the evaporation of toluene, PS-AA capsules retai ned a spherical shape and uniformity, whereas PS-AA/PS-BA capsules revealed a creased surface and broader size distribution. The microcapsules entrapp ed 30-40 wt% of magnetite, and the encapsulation yield of magnetite was 20- 40%. Glass membranes with 9.5, 5.25 and 1.42 mum pore size were employed an d 5-40 mum microcapsules were obtained depending on the pore size. When mag netite suspended in chloroform was used, magnetite capsules with broader si ze distributions were obtained because of the sticking of the droplets to t he membrane wall. The advantage of the membrane emulsification which provid es uniform sized droplets was lost.