THE APPLICABILITY OF CATASTROPHE-THEORY TO EMULSION PHASE INVERSION

Catastrophe theory, in particular the elementary cusp catastrophe, has been successfully applied to describe the qualitative features of cat astrophic phase inversion in emulsions, but quantitative, experimental tests of the cusp catastrophe did not yield satisfactory results. We have shown that the elementary butterfly catastrophe can fit experimen tal data from the literature with reasonable accuracy. The quality of the fit may be improved, but only at the cost of the introduction of m ore fit parameters with little or no physical significance. We present an expression derived from physical properties rather than mathematic al ones, on the basis of which all observed catastrophic phenomena can be qualitatively described. At values of the interfacial tension typi cal to coarse emulsions, this model predicts phase separation. However , phase inversion is generally observed under these conditions. We poi nt out that the assumptions that justify a thermodynamical treatment o f transitional inversion are not valid for catastrophic inversion. Our conclusions indicate that catastrophic phase inversion, unlike transi tional inversion, should be treated on a kinetic basis rather than a t hermodynamical one. (C) 1995 Academic Press, Inc.