Effect of process parameters on nanoemulsion droplet size and distribution in SPG membrane emulsification

A Shirasu-porous-glass (SPG) membrane with a mean pore size of 2.5 μm was used to produce an oil/water (O/W) nanoemulsion of flurbiprofen consisting of methylene chloride as the dispersed phase, polyvinyl alcohol (PVA) as the stabilizer and a mixture of Tween 20 and Tween 80 in demineralized water as the continuous phase. Emulsion droplets with a mean droplet size of 25 times smaller than the mean pore size and a narrow droplet size distribution were produced using 5% emulsifier at a feed pressure of 15 kPa. Under these conditions the z-average diameter and size distribution of the emulsion droplets formed were influenced by the type of surfactant, agitator speed (150-1200 rpm), feed pressure (15-80 kPa), stabilizer concentration (0-4, w/v) and the temperature of the continuous phase. Increasing the agitator speed and stabilizer concentration increased the z-average diameter and decreased the size uniformity. There was a linear relationship between the increased feed pressure and the decreased z-average diameter of the emulsion droplets. However, the uniformity of the size distribution decreased with increasing feed pressure. The continuous phase temperature played an important role in particle size and distribution. The nanoemulsion composed of oil, water, PVA and the surfactant mixture at the weight ratio of 10/100/1/5 was prepared using a SPG membrane at an agitator speed of 300 rpm, a feed pressure of 15 kPa and a continuous phase temperature of 25 °C. Our results indicated that these conditions led to relatively uniform emulsion droplets with a narrow size distribution and high zeta potential. This emulsion was stable for at least 13 h. Furthermore, the droplets in the emulsion containing the drug were not smaller but were more uniform with a narrower distribution compared to those without the drug.