Preparation of highly stable concentrated W/O nanoemulsions by PIC method at elevated temperature

Phase inversion composition (PIC) method is generally used to prepare nanoemulsions because of its relatively low energy costs and ease of formation. Most of the reported nanoemulsions are usually oil-in-water nanoemulsions. In this work, water-in-oil nanoemulsions in water/Span 80-Brij 35/paraffin oil system were prepared by the PIC method at elevated temperature. This method allows the formation of finely dispersed W/O nanoemulsions in this system. However, macroemulsions rather than nanoemulsions were prepared by PIC method at room temperature. As a result of the significant change of interfacial tension with temperature, the emulsion droplet size decreases from 50 μm to 82 nm with the increase in temperature from 25 °C to 80 °C. The droplet size of nanoemulsions prepared at 80 °C was in the range of 70–200 nm and the internal phase content could reach as high as 60 wt%. The obtained nanoemulsions were stable without obvious change in droplet size in two months. This study provides significant information for optimizing the formation of W/O nanoemulsions.