An insight into thermodynamic and association behaviours of cocamidopropyl betaine (CAPB) surfactant in water and water–alcohol mixed media

Abstract

This article presents new experimental data about the conductivity and surface of Cocamidopropyl Betaine (CAPB) surfactant in pure H2O and organic–H2O mixed solvent (methanol, MeOH; ethanol, EtOH and glycerol, GlyOH) media containing various mole fractions of alcohols over the temperature range 298.15 to 313.15 K, in steps of 5 K using conductometric and surface tension measurements. The experimental data for conductivity and surface tension have been used in order to determine the critical micelle concentration (CMC). It has been observed that the CMC increases with increasing temperature and proportion of alcohol. Moreover, the association constant ( $$K_{a}$$ ) of CAPB was also determined, depending on the conductivity data, using the Shedlowsky equation. The study showed that, as the temperature and alcohol ratio increased, the association constant of CAPB decreased. In addition, it was found that the CMC increased with MeOH > EtOH > GlyOH and the association behaviour was observed to be spontaneous. The thermodynamics behaviour of (CAPB) surfactant have been thoroughly assessed from the temperature dependence of the micellization and association constants. In all media studied, densities and refractive indices of CAPB were also measured under atmospheric pressure, in the solvents used at T = (298.15 K). The molal volume was estimated based on the density data and some additionally parameters such as molar refraction and the polarizability were also estimated and discussed depending on the refractive index values. These parameters have been utilized to comprehend the association and solvation behaviour of the CAPB surfactant.