Microscopic observation of emulsion droplet formation from a polycarbonate membrane

Real-time microscopic observations of the membrane emulsification process were performed using a novel membrane module and a microscope video system. The droplet growth and detachment processes from the membrane pores were analyzed from visual images taken during the experimental runs. A hydrophilic polycarbonate membrane with a mean pore size of 10 μm was employed. Microscopic observations of the oil droplet formation process from the membrane verified the continuous phase flow-driven droplet formation. This paper also describes the influences of the continuous phase flow velocity and the surfactant type on membrane emulsification. The use of anionic and nonionic surfactants resulted in successful membrane emulsification with no droplet coalescence at flow velocities greater than 0.1 m s−1. The droplet size of the resulting oil-in-water (O/W) emulsions decreased with an increase in the flow velocity, remaining almost constant at flow velocities greater than 0.4 m s−1. The emulsions prepared under these conditions had the average droplet sizes of about 20 μm and the coefficients of variation of 20–50%. In contrast, a cationic surfactant-containing system resulted in no droplet formation due to complete wetting of the membrane surface with the dispersed phase. An analysis of the surfactant–polycarbonate membrane interaction and contact angle measurements explained well the results that the membrane emulsification behavior critically depended on the type of surfactant used.