Dr. Marie-Esther Saint Victor

Manager, Applied Physics Group

Cognis Corporation Research & Technology

Discussion and Special Interests Group

ACS, Surface Science and Colloid Division

December 7, 2000

Title: Solution Thermodynamics as a tool in surfactant formulation. A review of the forces that govern synergistic interactions in surfactant mixtures comprising Alkylpolyglycoside (APG^®) surfactants and their deviation from the Regular Solution Theory.

Abstract: Strong synergistic interactions are usually observed in surfactant mixtures comprising Alkylpolyglycoside (APG^®) and nonionic surfactants. Both solution and interfacial properties of the mixtures are significantly enhanced, compared to the properties of the individual surfactants. Moreover, APG^® surfactants tend to increase the cloud points of nonionic surfactants.

Four major forces contribute to these interactions: (1) contribution from the break-up of the structure of water molecules as the temperature increases; (2) surfactant-water compatibility or antipathy; (3) self-association of surfactant molecules in solution; and (4) surfactant-surfactant interactions. The synergistic interactions in these mixtures exhibit strong temperature and concentration dependence. A “local composition Non-Randomness” causes a concentration-concentration fluctuation in the middle of the concentration range.

In an effort to model these interactions, excess thermodynamic properties of mixtures comprising APG^® as a co-surfactant were systematically investigated. The interactions are “non-ideal” and exhibit a strong deviation from the predictions of the Flory-Huggins Regular Solution Theory. The properties and efficiency of mixtures of APG^® with various ethoxylated surfactants are reviewed.