Aggregation behavior of silicone surfactants in ethylammonium nitrate ionic liquid

The aggregation behavior of two silicone surfactants (monomeric and Gemini) was studied by surface tension measurements in a room temperature ionic liquid, ethylammonium nitrate (EAN), at various temperatures. A series of parameters, including critical micelle concentration (CMC), surface tension at the CMC (γ _CMC), adsorption efficiency (pC ₂₀), and effectiveness of surface tension reduction (Π _CMC), were obtained. By comparing the silicone surfactants with traditional surfactants, we deduced that the surface activity of the silicone surfactants in EAN was superior to the activity of other surfactants. In addition, from the CMC values and their temperature dependence, we estimated the thermodynamic parameters of the micelle formation, \( \Delta G_m^0 \), \( \Delta H_m^0 \), and \( \Delta S_m^0 \). It was revealed that the micellization of the silicone surfactants is entropy driven at low temperature and enthalpy driven at high temperature. Isothermal titration calorimetry measurements were also carried out to study the micellization of Gemini silicone surfactant. ¹H NMR was performed to study the silicone surfactant micelle formation mechanism in EAN.