Synthesis and properties of ionic liquid-type Gemini imidazolium surfactants

A series of ionic liquid-type Gemini imidazolium surfactants with four-methylene spacer groups were synthesized ([C-n-4-C(n)im]Br-2, n = 10, 12, 14). The surface activity and thermodynamic properties of micellization between the Gemini imidazolium surfactants and their corresponding monomers ([C(n)mim]Br, n = 10, 12, 14) were compared by means of surface tension and electrical conductivity measurements. The values of cmc, gamma cmC, pc(20), Gamma(max), and A(min) derived from surface tension measurement at 25 degrees C suggest that the surface activity Of [C-n-4-C(n)im]Br-2 is higher than that of [C(n)mim]Br. While the thermodynamic parameters of micellization (Delta G(m)(degrees), Delta H-m(degrees). Delta S-m(degrees)) derived from electrical conductivity indicate that the micellization of [C-n-4-C(n)im]Br-2 is entropy-driven, aggregation of [C(n)mim]Br is entropy driven at low temperature but enthalpy-driven at high temperature. Finally, the activation energy of conductance (E.) that is associated with the effective charge is also obtained for [C-n-4-C(n)im]Br-2 and it is constant below the cmc, but it increases above the cmc. (C) 2008 Elsevier Inc. All rights reserved.