Dilational Viscoelasticity of Imidazole-Based Surface Active Ionic Liquids at the Air/Water Interface

Abstract

Two imidazole-based surface active ionic liquids (CnmimBr) were synthesized, and their aggregation behavior at the air/water interface was studied via an oscillating bubble method. The effects of the CnmimBr concentration, inorganic salts (NaBr and CaBr2), and temperature on the aggregation behavior were investigated. The results of the adsorption dynamics showed that the adsorption-controlled process dominated, but the relaxation process was not purely mono-exponential. The addition of inorganic salt or increase in temperature improved the surface activity of the CnmimBr and lowered the dynamic surface tension. The dilational rheological results revealed that the dilational modulus, elastic modules, and viscous modules increased with increasing oscillating frequencies, and the modulus reached a maximum value with increasing CnmimBr concentration. Increasing the temperature or adding inorganic salts (NaBr or CaBr2) decreased the dilational modulus. The elastic modulus was dominant for the CnmimBr layer, and the elastic modulus of C14mimBr was larger than that of C12mimBr.