The tremendous importance of evaporation from liquid dispersed systems for both processes and products has given rise to advanced treatment of the process per se with the leading scientists focusing on the colloidal forces influencing the rate of evaporation. This approach has clarified the kinetics during the initial part of the evaporation, but has provided no information about the decisive changes during later stages of the process.

This lecture will outline a phase diagram approach to evaporation from such systems, which provides detailed information about the phase changes taking place, but does not leave quantitative information about the rate of evaporation. The approach will focus on two factors that monitor the evaporation path. The first of these is the ratio of oil to water in the original emulsion and the second is the relative humidity of the atmosphere into which the evaporation takes place. Examples will be presented which determine the critical O/W ratio for the evaporation path to avoid the formation of gels, which reduce the evaporation rate as well as the surprisingly decisive effect of variation in the relative humidity.