Satoshi Iwamoto

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.

Preparation of gelatin microbeads with a narrow size distribution using microchannel emulsification.

The purpose of this study was to prepare monodisperse gelatin microcapsules containing an active agent using microchannel (MC) emulsification, a novel technique for preparing water-in-oil (W/O) and oil-in-water (O/W) emulsions. As the first step in applying MC emulsification to the preparation of monodisperse gelatin microcapsules, simple gelatin microbeads were prepared using this technique. A W/O emulsion with a narrow size distribution containing gelatin in the aqueous phase was created as follows. First, the aqueous disperse phase was fed into the continuous phase through the MCs at 40°C (operating pressure: 3.9 kPa). The emulsion droplets had an average particle diameter of 40.7 μm and a relative standard deviation of 5.1%. The temperature of the collected emulsion was reduced and maintained at 25°C overnight. The gelatin microbeads had a smooth surface after overnight gelation; the average particle diameter was calculated to be 31.6 μm, and the relative standard deviation, 7.3%. The temperature was then lowered to 5°C by rapid air cooling and finally dried. The gelatin beads were dried and could be resuspended well in iso-octane. The had an average particle diameter of 15.6 μm, and a relative standard deviation of 5.9%. Using MC emulsification, we were able to prepare gelatin microbeads with a narrow size distribution. Since this emulsification technique requires only a low-energy input, it may create desirable experimental conditions for microencapsulation of unstable substances such as peptides and proteins. This method is promising for making monodisperse microbeads.