Phase Behavior and Microstructure of Aqueous Mixtures of Cetyltrimethylammonium Bromide and Sodium Perfluorohexanoate

Abstract

The phase behavior and microstructure of aqueous mixtures of cetyltrimethylammonium bromide (C16TAB) and sodium perfluorohexanoate (FC5) were investigated as a function of total surfactant concentration, mixing ratio, and temperature. The aggregation behavior of both the pure components and several mixtures was studied via surface tension experiments, and analysis of the results using the regular solution model yielded a β value of −19.4, indicating highly nonideal mixing. The evolution of phase behavior from the FC5−water binary axis with the addition of C16TAB was of particular interest. Below the critical micelle concentration or cmc of FC5 (5.70 wt %), the addition of small amounts of C16TAB leads to the formation of large structures, including vesicles, between surfactant concentrations of 2 and 4 wt %. Above the cmc, FC5 forms small globular micelles in solution. The addition of C16TAB to the FC5 micelles leads to an increase in viscosity and eventually phase separation into two rodlike micellar sol...