A Comparison of Membrane Emulsification Obtained Using SPG (Shirasu Porous Glass) and PTFE [Poly(Tetrafluoroethylene)] Membranes

SPG (Shirasu porous glass) membrane emulsification used to prepare uniform polymeric microspheres is briefly reviewed, and the performance of a hydrophilically treated PTFE [poly(tetrafluoroethylerie)] membrane is described and compared with that of the SPG membrane. A mixture of styrene. divinyl benzene and hexadecane (HD) was extruded through the membranes and dispersed in an aqueous phase containing polyvinylalcohol (PVA) and sodium lauryl sulfate (SLS) as mixed stabilizers. A hvdrophilically treated PTFE membrane was used with a stainless steel mesh support so that the membrane would not expand to affect the pore size during the emulsification. The nominal pore size of the PTFE membrane was replaced with the calculated one using a theoretical expression derived from the force balance between the external pressure and the interfacial tension between oil and water phases. The emulsion droplets prepared with the PTFE membrane revealed a broader size distribution than those obtained with the SPG membrane, and the rate of emulsificaton was nearly same for both membranes. Droplet size control was readily possible. The performance was significantly affected by the adsorption behavior of the stabilizers on the membrane surfaces. The contact angle profile of oil droplets on the PTFE membrane implied that the hydrophilically treated PTFE membrane is still hydrophobic compared to the SPG membrane. This tendency was reflected by the dependence of the average droplet diameter (and coefficient of variation, CV) on the concentration and composition of mixed stabilizers.