Investigation On Aggregate Morphologies Of Cationic/Anionic Surfactants Mixture Containing Carboxylate Gemini Component In Aqueous Solution

Gemini surfactants have superior or even novel properties compared with the one-head-one-tail surfactants due to their unique molecular structure. On the other hand, binary mixtures of cationic and anionic surfactants have always attracted close attention of the researchers because of their diverse phase behavior. Thus, one can imagine that the aggregation behavior will probably be further enriched by introducing Gemini component into the cationic/anionic mixtures. Investigations on cationic/anionic mixtures containing Gemini component have been reported in recent years. However, most of them focused on adsorption or micellization of the mixed systems and few studies related to the aggregate morphologies of the mixtures. In this work, we investigated the aggregate morphologies in aqueous mixture of an anionic Gemini surfactant C11pPHCNa and a cationic conventional surfactant DTAB. The effect of pH on the self-assembly of the mixed system was firstly examined due to the carboxylate head of C11pPHCNa. Then at the designed pH12.00, where C11pPHCNa is nearly ionized into C11pPHC2-, we focused on the relationship between the aggregate morphologies and the macroscopic phase separation behavior in DTAB/C11pPHCNa aqueous surfactant two-phase system (ASTP) to understand the formation mechanism of ASTP. Some interesting observations and results in the present work are described as follows:1. The aggregates of DTAB/C11pPHCNa mixture (CT=12mmol·L-1, R=4.5:1) transformed from vesicles to worm-like aggregates and finally precipitation when the pH of the aqueous solution decreased, which was attributed to the hydrolysis of the carboxylate head of C11pPHCNa. Accordingly, a minimum appeared in the change of the turbidity of mixed solution as a function of pH.