Molecular Interactions in Binary Surfactant Solutions: Effect of pH

Abstract

By using surface tension and conductivity measurements, the colloid-chemical properties of the mixtures of cationic hexadecylpyridinium bromide with nonionic Triton X-100 surfactants were investigated both in the bulk solution and at air/solution interface at different pH values. The composition of mixed micelles and adsorption layers, parameters of molecular interactions in mixed micelles βm and adsorption layers βσ, as well as standard free energies of micelle formation ΔG0mic and adsorption ΔG0ads were calculated. It was found that molecules of the nonionic surfactant presumably dominate in the mixed micelles and adsorption layers. It was shown that βm and βσ have negative values, which indicate the strengthening of intermolecular interactions in the mixed micelles and adsorption layers. Based on the data obtained, it was suggested that ion-dipole interactions are involved in the formation of intermolecular structures between nonionic and cationic surfactants in aqueous solution and at the air-solution interface. It was shown that βm, βσ as well as ΔG0mic and ΔG0ads parameter depends on the solution pH value. The complex interplay of ion-dipole, protonation and chelation processes, which occur in the surfactant mixtures at different pH and affect the strength of intermolecular interaction, should be taken into account for data analysis.

Kinetic and thermodynamic investigations of surfactants adsorption from water by carbide-derived carbon

“…It might also be assumed that chelation with Na þ ions of the anionic surfactant with the surface oxygen atoms, possessing the lone electron pair, might also contribute to SDBS adsorption on the CDC surface. [62,63] For HDPB, the adsorption capacity increased from 457 to 479 mg/g with increasing the solution pH from 2.5 to 8 and notably decreased to 449 mg/g at pH 10. The amount of the adsorbed HDPB increased with pH, presumably due to reducing the repulsion forces between HDPB and CDC.…”