Abstract
The micellar growth of dicationic gemini surfactants with the general formula C(m)H2(m+1)(CH3)(2) N+(CH2)(2) N+ (CH3)(2)CmH2m+1, 2Br(-) as a function of alkyl chain length (m =10, 12, 14) and effect of addition of alcohols (C6OH. C7OH, C8OH) and amines (C6NH2, C7NH2, C8NH2) in the absence and presence of organic salts (NaSal. NaTos) have been investigated by viscosity measurements at 30 degrees C. A simultaneous presence of organic salt and alcohol/amine induced aggregate morphologies in the gemini micellar systems by giving high viscosity values. As the chain length of the organic additive increases, the viscosity increases with increase in additive concentration and the extent of the effect followed the sequence: C-6 < C-7 < C-8. For the longer alkyl chain geminis, a micellar growth resulting in a transition to nonspherical micelles occurs first, giving rise to high viscosity values in the order m = 10 < 12 < 14. In comparison to the gemini surfactants, no effect was observed with the corresponding conventional surfactants of equal chain length, i.e., Cm(H)2(m+1)(CH3)(3) N+Br-, even in the presence of organic salts of the same concentration used with the geminis. The results are explained in terms of mixed micelle formation and coulombic interaction. (C) 2012 Elsevier B.V. All rights reserved.