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 (\(\Delta G_{\text{m}}^0 \), \(\Delta H_{\text{m}}^0 \), \(\Delta S_{\text{m}}^0 \)) 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.