Synthesis, thermal stability and surface activity of imidazolium monomeric surfactants

Abstract

Abstract The renewable raw material-based imidazolium cationic monomeric surfactants have been prepared and characterized by FTIR, 1HNMR and TGA. The conductometric study of 3-(2-(decanoyloxy)ethyl)-1-methyl-1H-imidazol-3-ium-bromide (capric surfactant) and 3-(2-(octadecanoyloxy)ethyl)-1-methyl-1H-imidazol-3-ium-bromide (stearic surfactant) with different concentrations at 298K, 303K, 308K and 313K in ethanol; indicates that these surfactants behave as weak electrolytes. The thermodynamic parameters calculated from conductivity measurements indicate that micellization is favoured over dissociation process. The results of density and viscosity measurements have been satisfactorily explained by well-known equations with their allied parameters. The surface-active properties of capric and stearic surfactant have been measure at 298K in water and ethanol. The Gibb's adsorption isotherm confirm that derivative of surface tension with respect to natural logarithm of concentration is negative, indicating that adsorption is positive in nature i.e. surface tension of the solution is lowered by addition of surfactant molecules. The thermo-gravimetric analysis (TGA) indicates that these surfactants are thermally stable up to 370 °C. Activation energy for thermal decomposition was found to be in the range of 14.00–26.06 kJ/mol and thermal stability is more for surfactants having higher hydrocarbon chain than lower one. The information collected from conductance, density and viscosity as well as surface tension measurements has shown that there is significant interaction between surfactant molecules at certain concentration (CMC).