Aqueous solutions of the double chain cationic surfactants didodecyldimethylammonium bromide and ditetradecyldimethylammonium bromide with Pluronic F68: Dynamic surface tension measurements

The adsorption kinetics of mixtures of the non-ionic copolymer Pluronic F68 with two double chain cationic surfactants didodecyldimethylammonium bromide (di-DDAB) and ditetradecyldimethylammonium bromide (di-TDAB) is studied with dynamic surface tension experiments. A time dependent synergy is observed, in most of the mixtures. In a few cases, hindrance effects are observed. Clusters are formed at concentrations well below the critical micelle concentration (cmc), at the critical aggregation concentration (cac). The presence of the copolymer stabilizes the electrostatic repulsion between the positively charged quaternary ammonium headgroups of di-DDAB and di-TDAB. The electrostatic repulsion between the polar parts of the same and adjacent surfactant molecules is minimized. We compare our results with recently published results, using mixtures of these double chain cationic surfactants with hydroxypropylmethylcellulose.