Micelle formation of ionic amphiphiles. Thermochemical test of a thermodyanamic model

Abstract

Differential enthalpies of dilution of 28 wt % aqueous sodium dodecyl sulphate solution have been measured using a titration microcalorimeter. In this way titration curves were determined in the concentration range 0–0.040 mol dm^–3 at three different temperatures. Theoretical titration curves were calculated using values for concentrations of the amphiphile in the monomer and micellar states derived from the thermodynamic model for the association of ionic amphiphiles proposed by Jönsson and Wennerström. The computational procedure is described. The agreement between the calculated and experimental curves is good, which shows that the model can give quantitative predictions of the micellization process. It was observed that the decreasing monomer concentration with increasing amphiphile concentration above the c.m.c. requires the quantitative evaluation of the composition of the reaction solutions in order to derive correct values for the enthalpy of micelle formation of ionic amphiphiles from results of calorimetric measurements.