EMF and Microcalorimetry Studies Associated with the Binding of the Cationic Surfactants to Neutral Polymers

EMF measurements on binary mixtures of the cationic surfactants tetradecyltrimethylammonium bromide and tetradecylpyridinium bromide and a range of nonionic polymers have been carried out. The existence of polymer/surfactant complexes was found for those polymers whose microstructures contain side groups with hydrophobic character. Isothermal titration microcalorimetry measurements were also taken to obtain more information about the polymer/cationic surfactant complexes. An examination of the dependence of the monomer surfactant concentration following the binding showed that “free” micelles are formed in solution before the polymers become “saturated” with bound surfactant. In some cases these free micelles occur in solution before the critical micellar concentration of the pure surfactant an effect which is thought to occur due to an excess counterion concentration in the microenvironment at the vicinity of the complex. Finally a comparison of the present data with the binding behavior of these polymers with sodium dodecyl sulfate (SDS) allows us to identify the roles of electrostatic and hydrophobic interactions that take place to allow the formation of stable polymer/surfactant complexes.