Dynamic surface tension studies of mixtures of hydroxypropylmethylcellulose with the double chain cationic surfactants didodecyldimethylammonium bromide and ditetradecyldimethylammonium bromide

•Adsorption kinetics up to several hours.•Time-dependent synergistic effects.•Two induction times are observed, 44mN/m at the induction time II.•Critical association concentrations estimated. Dynamic and equilibrium surface tension experiments were carried out to study the adsorption kinetics of mixtures of the nonionic polymer hydroxypropylmethylcellulose (HPMC) with two double chain cationic surfactants, didodecyldimethylammonium bromide (di-DDAB) and ditetradecyldimethylammonium bromide (di-TDAB). Results are obtained concerning the capacity of the surfactants to lower surface tension, the rate of lowering, the extent of adsorption at the interface, the possibility of changing conformation during and after adsorption, and the interactions between the adsorbed molecules. A time-dependent synergy is observed in most of the mixtures, while in a few cases hindrance effects are observed. The interaction of HPMC with the double chain cationic surfactants resulted in complexes with higher surface activity than the two components alone. Two induction times were observed, the second ones being more significant in the presence of di-TDAB. At concentrations well below the critical micelle concentration (cmc), the critical aggregation concentrations (cac), evidence for clusters is observed.