Micellar growth of m-2-m type gemini surfactants (m = 10, 12, 14) with higher chain length alcohols/amines (C6-C8) in the absence and presence of organic salts (sodium salicylate, sodium tosylate)

The micellar growth of dicationic gemini surfactants with the general formula CmH2m + 1(CH3)2 N+(CH2)2 N+(CH3)2CmH2m + 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 °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: C6 < C7 < C8. 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., CmH2m + 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.

Variation of the viscosity of the solutions as a function of the concentration of additives (alcohol/amine of equal chain length) to 0.01 M 14-2-14 solution in the absence (open symbols) and presence (filled symbols) of 0.001 M NaSal: (,) C8H17OH, (,) C8H17NH2.Highlights► Effect of additives on the m-2-m gemini micelles have been studied. ► Sodium salicylate, sodium tosylate, alcohols and amines lead to viscosity enhancement. ► Combined presence of salt + organic additives produces synergism.