Interacting CnEm non-ionic micellar systems

Abstract

Trends in the temperature dependence of the effective intermicellar attraction ε(T) have been calculated for a series of non-ionic ethylene oxide surfactants C_nE_m[C_nH_{2n+ 1}(OCH₂CH₂)_mOH] using the penetrable-sphere model of Widom and Rowlinson to model the cloud curve. The form of ε(T) may be analytically related to the critical exponent and to the shape of the coexistence curve close to the lower consolute solution temperature in the mean-field approximation. The results show that ε(T) calculated from the scaled cloud curves increases more rapidly with temperature as the alkyl chain length is varied over the range n= 8, 10, 12 and 16 while little effect of headgroup size is seen in the range of m available. The application of the concept of corresponding states to these systems is discussed and the results are related to two recent alternative approaches and to the experimental evidence for the characterisation of the structure of C_nE_m micelles.