Micellar properties of cetyltrimethylammonium bromide in an acetonitrile–water mixture: Conductometric and fluorescence studies

The effect of acetonitrile (ACN) on the micellization of a cationic surfactant, cetyltrimethylammo-nium bromide (CTAB), in aqueous solutions at different temperatures was studied. The critical micellar concentration (CMC) as well as the degree of counter ion dissociation (a) of CTAB in aqueous ACN mixtures (10-20 % v/v) at various temperatures (291.2-298.2 K) were determined by electrical conduc-tivity measurements, while steady-state fluorescence measurements were used to determine several CMCs (for comparison) and a micellar aggregation number (N-agg) as well. At a fixed temperature, both an increase in CMC and a decrease in N-agg were observed for an increase in ACN in the solvent mixture. With a temperature increase, CMC values increased for 10 % (v/v) ACN, while for both 15 % and 20 % (v/v) ACN, CMC values were a minimum at T = 295.2 K with a temperature increase. In addition, some aspects related to the Krafft temperature behavior of CTAB in the examined micellar systems are discussed.