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. butanediy1-1,4-bis(tetradecyldimethylammonium bromide) (14-4-14), pentanediy1-1,5-bis(tetradecyldimethylammonium bromide) (14-5-14) and hexanediy1-1,6-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 (Delta G(m)(0)), a rough increase was observed in the values of degree of counter ion dissociation (alpha) and a decrease was obtained in values of average aggregation number (N-agg) and Stern-Volmer constant (K-SV,). 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 (d(H)) performed at a concentration of 10 mmol kg(-1) shows that the hydrodynamic diameter (d(H)) is less than 70 nm for most of the system except at some of the composition where slightly higher values were obtained. (C) 2016 Elsevier B.V. All rights reserved.