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 ([Cn-4-Cnim]Br2, n=10n=10, 12, 14). The surface activity and thermodynamic properties of micellization between the Gemini imidazolium surfactants and their corresponding monomers ([Cnmim]Br, n=10n=10, 12, 14) were compared by means of surface tension and electrical conductivity measurements. The values of cmc, γcmcγcmc, pc20pc20, ΓmaxΓmax, and AminAmin derived from surface tension measurement at 25 °C suggest that the surface activity of [Cn-4-Cnim]Br2 is higher than that of [Cnmim]Br. While the thermodynamic parameters of micellization (ΔGm○, ΔHm○, ΔSm○) derived from electrical conductivity indicate that the micellization of [Cn-4-Cnim]Br2 is entropy-driven, aggregation of [Cnmim]Br is entropy-driven at low temperature but enthalpy-driven at high temperature. Finally, the activation energy of conductance (EaEa) that is associated with the effective charge is also obtained for [Cn-4-Cnim]Br2 and it is constant below the cmc, but it increases above the cmc.

The thermodynamic parameters of micellization obtained from conductivity measurements indicate that negative values of ΔGm○ arise due to large positive ΔSm○ values, and so the micellization process is entropy-driven.Figure optionsDownload as PowerPoint slide