Surface adsorption and thermodynamic properties of mixed system of ionic liquid surfactants with cetyltrimethyl ammonium bromide

Abstract

The effects of temperature and concentration of CTAB added into imidazolium-based ionic liquids (CnmimBr, n = 10, 12, 16) solution were investigated, and surface active parameters and aggregation of these surfactants were explored by surface tension and conductivity measurements, which include critical micelle concentration (CMC), maximum surface excess concentration (Γmax), minimum surface area per surfactant molecule (Amin), surface tension at the CMC (γCMC), adsorption efficiency (pC20), and surface pressure (ΠCMC), as well as thermodynamic parameters of micellization. The results were reported in the presence of CTAB at 0, 4, 8, 12, and 16 mM for C10mimBr, 0, 0.2, 0.4, 0.8, and 1.2 mM for C12mimBr, and 0, 0.04, 0.08, 0.12, and 0.16 mM for C16mimBr in mixed systems. The increase of the CMCs with temperature were observed, while pC20, Γmax, and standard entropy of aggregation were decreased, indicating that the aggregation is an enthalpy-driven process within the temperature limits of the present study. FT-IR and 1H NMR measurements revealed that the changes mentioned above were controlled by the electrostatic effect and hydrophobic interactions between CTAB and ILs molecules.