A thermophysical approach to the behaviour of gels and complex micellar solutions

DSC analysis, conductimetric and rheological techniques have been used to investigate the structural changes able to develop in the [water + hexadecyltrimethyl ammonium bromide (CTAB) + phenol] ternary micellar system. Specific, mainly electrostatic, interactions at the micellar interface between the surfactant polar head groups and phenol give rise to a swelling of aggregates into worm‐like micelles as evidenced by large changes of viscosity of the mixture in some phenol/CTAB ratio and temperature ranges. A thermophysical approach allowed us to determine the formation of a strong 1:1 complex between CTAB and phenol, as evidenced by either the viscoelastic properties of the solution or the formation of thermoreversible gels. At low temperature, a crystallized molecular surfactant complex is also observed. Its melting point differs from the Krafft temperature of CTAB. © 2003 Society of Chemical Industry