Effects of Solvent Media and Temperature on the Self-Aggregation of Cationic Dimeric Surfactant 14−6−14, 2Br− Studied by Conductometric and Fluorescence Techniques

To explore how the solvent characteristics influence the self-aggregation of the cationic dimeric surfactant hexamethylene-1,6-bis(tetradecyldimethylammonium bromide) (14−6−14, 2Br−) and to obtain various energetic parameters, conductometric experiments were performed on the binary mixtures of three organic solventsviz., 2−methoxyethanol (ME)−, acetonitrile (AN)−, and formamide (FA)− water (WR) at different temperatures ranging from 298.15 to 323.15 K. The steady state fluorescence measurements allowed us to calculate the average aggregation number (N agg ) and the air-bulk phase surface tension helped us to correlate the solvent cohesive energy density with Gibbs energy of micellization (ΔG 0 m ). The results showed that, although micellization process becomes less favorable with the increase in volume % of the ME, AN and FA in the binary mixed media, the increment in the cmc below 20% (v/v) of the organic solvents is comparatively less showing the predominance of WR character in the bulk phase. Because of the decrease in Gibbs interfacial energy contribution (ΔG 0 interf ) to ΔG 0 m , the average aggregation number (N agg ) decreased with the increase in the volume % of the organic solvent in the mixed media. As the enthalpy of micellization became more negative, the corresponding entropy change became less positive and enthalpy−entropy compensation phenomenon was observed for the micellization of 14−6−14, 2Br− in all the mixed media in the studied temperature range.