Thermodynamics of micelle formation by 1-methyl-4-alkylpyridinium halides

This paper reports enthalpies of micellization for a series of 1-methyl-4-alkylpyridinium halide surfactants at 303.2 K with different lengths and degrees of branching of the 4-alkyl chain and different sizes of counterions using two microcalorimeters (LKB 2277 and Omega Microcal). The standard enthalpy of micellization (DELTAH-degrees(m)) becomes more exothermic with increasing chain length and with increasing size of the halide counterion. No trend could be observed with respect to the degree of branching of the alkyl chain. Critical micelle concentrations (cmc) were determined as a function of temperature using conductometry. These cmc values were used to calculate the standard Gibbs energy of micellization (DELTAG-degrees(m)) according to the phase separation model. From this we calculated the standard enthalpy of micellization (DELTAH-degrees(m)), which was compared with the microcalorimetric enthalpies of micellization.