Effect of ionic liquid C2mimBr on rheological behavior of Gemini surfactant 12-2-12 aqueous solution

The rheological properties of Gemini surfactant 12-2-12 solutions in the absence and presence of ionic liquid C2mimBr have been investigated systemically. The results have shown that the 12-2-12 solutions with lower concentrations exhibit typical Newtonian fluid behavior and predominately viscous. The solutions with higher surfactant concentration show shear thinning property and have viscoelastic nature. However, the addition of C2mimBr changes the rheological properties of 12-2-12 solutions significantly. The steady-shear viscosity and the plateau modulus increase obviously, and the mixed solutions fit the Maxwell’s mechanical model as linear viscoelastic fluid. The effect of C2mimBr on surfactant solution mainly derives from the strong compress effect of counter-ion on electrical double layer near hydrophilic head groups of 12-2-12, the π-π stacking among imidazole rings, and the hydrogen bonding interaction between N+ of [C2mim]+ and water. These comprehensive effects promote the entanglement of surfactant micelles and thus leading to the formation and further compaction of network structures, which have been confirmed directly by cryo-scanning electron microscopy (cryo-SEM) micrographs.