Surface tension of the oppositely charged sodium poly(styrene sulfonate) /benzyldimethylhexadecylammonium chloride and sodium poly(styrene sulfonate)/polyallylamine hydrochloride mixtures

Oppositely charged polyelectrolyte/surfactant and the coacervate polyanion/polycation mixtures are known to display complex properties at water/air interface which are not fully elucidated. The change in surface tension of the anionic polyelectrolyte sodium poly(styrene sulfonate) (NaPSS) with either benzyldimethylhexadecylammonium chloride (BAC) as the cationic surfactant or the cationic polyelectrolyte polyallylamine hydrochloride (PAACl) as a function of temperature and added salts was investigated. Neither of the pure polyelectrolytes showed significant surface activity; however, addition of oppositely charged surfactant or polyelectrolyte to varying concentrations of NaPSS solutions had changed the surface activity drastically. The surface tension of the NaPSS/BAC complex is lower than that of pure BAC surfactant. The surface tension of these complexes showed significant decrease with increasing temperatures and the surface excess entropy was deduced from these measurements. Addition of ionic salts enhanced the association of the polyelectrolyte/surfactant mixture but had little effect on the polyelectrolytes coacervate. The surface tension of low concentrations of NaPSS/PAACl coacervate displayed a peak which can be attributed to charge inversion.