How to calculate phase diagrams for microemulsions — a simple rule

For nonionic microemulsions a simple rule is given to achieve a semiquantitative prediction of phase boundaries. In particular, we consider the phase boundaries between a single-phase microemulsion and a 2Φ-microemulsion (i.e. a microemulsion coexisting with a water- or an oilrich phase), as well as between a 2Φ-microemulsion and a 3Φ-microemulsion (i.e. a microemulsion coexisting with a water- and an oilrich phase). Our method treats weak and strong surfactants within a unified approach.