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 ([C₁₂-s-C₁₂im]Br₂, s = 2, 4, 6) have been investigated by means of surface tension, electrical conductivity, dynamic light scattering and fluorescence measurements. The values of cmc, γ cmc, Γ max, A min, π cmc, pc₂₀ and cmc/pc₂₀ suggest that the shorter the spacer, the higher the surface activity of [C₁₂-s-C₁₂im]Br₂ is. The cmc and γ 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 ( [graphic removed] , [graphic removed] , [graphic removed] ) indicate that the micellization of [C₁₂-2-C₁₂im]Br₂ and [C₁₂-4-C₁₂im]Br₂ is entropy-driven, whereas aggregation of [C₁₂-6-C₁₂im]Br₂ 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 [C₁₂-s-C₁₂im]Br₂.