Aggregation and thermodynamic properties of ionic liquid-type gemini imidazolium surfactants with different spacer length

The aggregation behavior and thermodynamic properties of micellization for the ionic liquid-type gemini imidazolium surfactants with different spacer length ([C-12 - s-C(12)im]Br-2, s = 2, 4, 6) have been investigated by means of surface tension, electrical conductivity, dynamic light scattering and fluorescence measurements. The values of cmc, gamma(cmc), Gamma(max), A(min), pi(cmc), pc(20) and cmc/pc(20) suggest that the shorter the spacer, the higher the surface activity of [C-12-s-C(12)im]Br-2 is. The cmc and gamma(cmc) values are decreased significantly in the presence of sodium halides, and the values decrease in the order NaCl<NaBr<NaI. The thermodynamic parameters of micellization (Delta G(m)(0), Delta H-m(0), Delta S-m(0)) indicate that the micellization of [C-12-2-C(12)im]Br-2 and [C-12-4-C(12)im]Br-2 is entropy-driven, whereas aggregation of [C-12-6-C(12)im]Br-2 is enthalpy-driven at lower temperature but entropy-driven at higher temperature. Finally, the fluorescence measurements show that the micropolarity of micelles increases but the aggregation numbers decrease with increasing the spacer length of [C-12-s-C(12)im]Br-2.