A generalization of Widom’s model of microemulsions.

We construct a generalization of Widom’s model of microemulsions which permits the contact of polar and apolar material. This is necessary to explain the behavior of certain short chain amphiphilic systems. The same interactions have previously been proposed by Robledo, but the partition function which he derived from these interactions and discussed in detail in his paper (a partition function of a spin 1 Ising system) does not quite represent these interactions. We arrive at a spin 3/2 Ising model with nearest neighbor interactions. Robledo’s spin 1 form is recovered as an approximation whose range of validity is discussed. We particularly investigate the limit towards Widom’s model, the progression of Winsor microemulsion, and the question of retrograde solubility in the binary water–amphiphile subsystem, which has been advocated by Robledo. [ABSTRACT FROM AUTHOR]