Effect of ethylene glycol and propylene glycol on the aggregation of alkanediyl-α,ω-bis(tetradecyldimethylammonium bromide) (14-s-14; s = 4-6) gemini surfactants

The effect of addition of two co-solvents (ethylene glycol (EG) and propylene glycol (PG)) on the aggregation properties of three cationic gemini surfactants (viz. butanediyl-1,4-bis(tetradecyldimethylammonium bromide) (14-4-14), pentanediyl-1,5-bis(tetradecyldimethylammonium bromide) (14-5-14) and hexanediyl-1,6-bis(tetradecyldimethylammonium bromide) (14-6-14)) has been studied by conductance, steady state fluorescence and dynamic light scattering measurements at 298 K. The weight percentage of these co-solvents varied in between 0 and 50% at an interval of 5% up to 20% and then 10% up to 50%. Micellization is delayed by the addition of co-solvents; consequently, a progressive increase was observed in critical micelle concentration (cmc) and Gibbs free energy of micellization (ΔGm0), a rough increase was observed in the values of degree of counter ion dissociation (α) and a decrease was obtained in values of average aggregation number (Nagg) and Stern-Volmer constant (KSV). At low weight percentage (up to 15%) of co-solvents, 14-s-14 (s = 4-6) geminis are found to be almost equally prone to micellization both in EG-water (EG-WR) and in PG-water (PG-WR) mixed media whereas at high weight percentages they are more prone to micellization in EG-WR than in PG-WR mixed media. The measurements of hydrodynamic radius (dH) performed at a concentration of 10 mmol kg− 1 shows that the hydrodynamic diameter (dH) is less than 70 nm for most of the system except at some of the composition where slightly higher values were obtained.