Cationic silicon-based gemini surfactants: Effect of hydrophobic chains on surface activity, physic-chemical properties and aggregation behaviors

A series of cationic silicon-based gemini surfactants (C-m-P-Si-C-m) having different hydrophobic chains length (m = 8, 10, 12,14, 16, 18) were synthesized. Subsequently, surface parameters including equilibrium surface tension (gamma cmc), critical micelle concentration (CMC), surface pressure at CMC (Pi(cmc)) and maximum surface excess(Gamma(max)) were calculated according to the surface tension measurements. The importance of hydrophobic chains length on the surface activity of Cm-PSi-Cm was revealed in detail. With the increasing hydrophobic chains length, the equilibrium surface tension gamma(cmc)) values follow the order of C-8-PSi-C-8 > C-10-PSi-C-10 > C-12-PSi-C-12 < C-14-PSi-C-14 < C-16-PSi-C-16 < C-18-PSi-C-18. The thermodynamic parameters of micellization process, namely, standard Gibbs free energy (Delta G(0m)), enthalpy (Delta H-m(0)) and entropy (Delta S(0)m), were derived from conductivity measurements at different temperatures. The aggregation of the cationic silicon-based gemini surfactants (C-12-PSi-C-12) in aqueous solution at different concentrations was studied by DLS and TEM measurements. The formation of micelles and vesicles in C-12-PSi-C-12 solutions was observed at a concentration well above the CMC. Moreover, the morphology of vesicles changed from sphere to rod-like, dumbble-like and finally string dumbbell-like with the increasing of the surfactant concentration. (C) 2017 Published by Elsevier B.V. on behalf of The Korean Society of Industrial and Engineering Chemistry.