Effect of Polar Organic Solvents on Self‐Aggregation of Some Cationic Monomeric and Dimeric Surfactants

Surface and micellization behavior of some cationic monomeric surfactants, viz., cetyldiethylethanolammonium bromide (CDEEAB), cetyldimethylethanolammonium bromide (CDMEAB), tetradecyldiethylethanolammonium bromide (TDEEAB) and dimeric surfactants, i.e., alkanediyl‐α, ω‐bis(dimethylhexadecylammonium bromide) (C 16 ‐s‐C 16 , 2Br − where s = 4, 12), butanediyl‐1,4‐bis(dimethyldodecylammonium bromide (C 12 ‐4‐C 12 , 2Br − ) and 2‐butanol‐1,4‐bis(dimethyldodecylammonium bromide) (C 12 ‐4(OH)‐C 12 , 2Br − ), was studied in water‐organic solvents [10 and 20 % v/v ethylene glycol (EG) and diethylene glycol (DEG)] by conductivity, surface tension and steady‐state fluorescence methods at 300 K. The main focus of the present work is on the study of the effect of organic solvents on the critical micelle concentration (CMC), Gibbs free energy of micellization (Δ G ° m ), Gibbs free energy of transfer (Δ G ° trans ), Gibbs adsorption energy (Δ G ° ads ) and some interfacial parameters such as the surface excess concentration (Γ max ), minimum area per surfactant molecule ( A min ) and surface pressure ( π CMC ). The aggregation number ( N agg ) and Stern‐Volmer quenching constant ( K SV ) were also determined by the steady‐state fluorescence method. It was observed that N agg decreased with increasing volume percent of organic solvent. The results exhibited an increase in CMC in water‐organic solvents as compared to the respective surfactants in pure water. The negative values of Δ G ° m and Δ G ° ads indicate a spontaneous micellization process. The thermodynamics of micellization revealed that the micellization‐reducing efficiency of glycols increases with the concentration and the number of ethereal oxygens in the glycol.