Study of conductivity, contact angle and surface free energy of anionic (SDS, AOT) and cationic (CTAB) surfactants in water and isopropanol mixture

Abstract

The thermodynamic properties of cationic surfactant CTAB (cetyltrimethylammonium bromide), anionic surfactant SDS (sodium dodecyl sulfate), and AOT (Aerosol OT) in pure water and 0.1, 0.2, 0.3, and 0.4 volume fraction of isopropanol were observed by measuring the conductivity at 298.15 K. Various physicochemical properties like CMC, α and the thermodynamic properties like standard free energy of micellization (∆Gmo), the free energy of surfactant tail transfer (∆Gtranso) were calculated. Also, (log S1 and log S2), α, CMC, K0KCMC, ∆Gmo and ∆Gtranso are correlated with the volume fraction of isopropanol. The result revealed a sharp increase in conductivity with an increase in surfactant concentration. With the increasing isopropanol content in the solvent composition, the critical micelle concentration (CMC) of the CTAB and SDS increased. The degree of micellar dissociation (α) as well as the Gibbs' free energy was found to be increased with the increasing volume fraction of isopropanol. The correlation of ∆Gmo with the solvent parameters and the solvophobic parameter were also included. The contact angle and surface free energies over the aluminum foil surface were also evaluated using a drop shape analyzer (DSA-25E).