MICELLAR GROWTH STUDY BY MICROCALORIMETRY IN CTAB SOLUTIONS

Microcalorimetry experiments were carried out on aqueous micellar solu tions of hexadecyltrimethylammonium bromide (CTAB) in the presence of potassium bromide (KBr). We have investigated the effect of surfactant concentration and of the salt content upon the specific heat. The cur ves of the specific heat versus temperature exhibit a maximum resultin g from the transition between spherical and elongated micelles. The te mperature T-max of these maxima depends on surfactant and salt concent ration as expected from simple theoretical arguments. Static and dynam ic light scattering experiments were performed on the same systems. Th e results show that light scattering and microcalorimetry experiments yield a different kind of information: blob size and variation of the micellar length. Microcalorimetry provides an interesting tool for det ermining the micellar growth.