Phase behaviour of non-ionic surfactant-p-xylene-water systems during the phase inversion process

The present paper describes briefly the apparatus and the different experimental techniques used to characterise the p-xylene-water-surfactant dispersion system. Phase inversion maps for the p-xylene-water-non-ionic surfactant system were developed. It was found that, contrary to what was previously thought, the reduction in drop size could occur during both 'stable catastrophic' and 'transitional' inversions. The presence of multiple emulsions was also investigated. It was found that multiple emulsions present before phase inversion could, after phase inversion, form single emulsions and vice versa. For the polyoxyethylene sorbitan monolaurate (SML) surfactants used (Tween20 and Span20), transitional inversion could occur either at low volume fraction or high volume fraction, leaving a gap in the middle range of water volume fraction where inversion did not occur. The gap reduced with increasing SML concentration. It was also found that the transitional inversion is not reversible when the blend Tween20/Span20 is used. For the polyoxyethylene nonylphenyl ether (NPE) surfactant system (Igepal co720/Igepal co520), transitional inversion occurred in the range of medium to high water volume fraction. The range where transitional inversion occurred, broadened when NPE concentration was increased. The application of a mixed non-ionic surfactant model to the NPE and SML systems was also investigated. (C) 1999 Elsevier science B.V. All rights reserved.