Calorimetric Analysis of Vesicular Systems

A number of studies of micellar aggregation in aqueous solutions of ethylene oxide-propylene oxide block copolymers — using high sensitivity differential scanning calorimetry (HSDSC) — are reviewed. The review attempts to show how the calorimetric output can be analysed, using a model fitting procedure, to obtain estimates for various thermodynamic parameters, which characterise the micellization event, as observed by HSDSC. These important parameters include: T_1/2 the temperature at which half the surfactant has been incorporated into micelles; H_cal — the calorimetric enthalpy for the process which is measured by integration of the calorimetric output; H_vH — the van't Hoff enthalpy — which characterises the functional dependence of the equilibrium composition of the system upon temperature and which is derived from the application of the van't Hoff isochore to the data analysis procedure; C_p — the heat capacity change between the initial and final states;and n the aggregation number.Using this data it is possible to examine how extent of aggregation functionally varies with temperature. Subsequent interpolation of these thermal aggregation plots permits an examination of how the extent of aggregation is affected by changes in solution composition under isothermal conditions. A large body of data is presented which shows how co-solvents, co-solutes and pH affect the aggregation process in aqueous solution.This revised version was published online in November 2005 with corrections to the Cover Date.