THE ROLE OF SWELLING METHODS IN SURFACTANT PHASE SCIENCE - PAST, PRESENT, AND FUTURE

The foundation for surfactant phase science was established largely using isoplethal phase study methods, but some use has been made of qualitative isothermal penetration experiments. In 1987 a quantitative swelling method (the Diffusive Interfacial Transport method) was reported in which the analysis of phase compositions is based on refractive index data. Experience obtained to date during use of this DIT-NDX method is reviewed. These investigations have demonstrated the considerable value of swelling studies, but revealed serious flaws in the DIT-NDX method. Swelling studies are exceptionally efficient, reliable, and provide considerable information regarding the physical science of the system in addition to the phase diagram. Unfortunately, this method is incapable of accurately defining the compositions of many birefringent phases. A DIT-IR method, presently under development, should resolve this problem. Analysis of composition using the DIT-IR method will be based on infrared data obtained using a near-infrared microscope. In addition to providing better composition data, infrared studies are expected to provide information on conformational structure, crystal hydration, and hydration thermodynamics. The future of swelling methods is discussed.