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Dramatic differences in the structure of mixed micelles of long chain amine oxides and sodium dodecylsulfate are noted as a function of composition. In the L1 micellar pseudophase, a sphere-to-rod transition driven by ion-dipole interactions between the dissimilar headgroups leads to synergisms in aqueous solution thickening, Ross-Miles foaming, and nonpolar oil solubilization. For example, an astounding seven orders of magnitude increase in the zero shear viscosity and viscoelastic properties are observed at a single total surfactant concentration. The sphere-to-rod transition can be viewed in FT-IR by examining both the CH2 stretching for the methylene tails, and the S-O stretching modes for the sulfate headgroups.

Dissolution of calcium salt of a long chain fatty acid or soap scum is a major challenge for hard surface cleaners since soap scum forms when soap is exposed to hard water and has very low water solubility. In this paper, the aqueous equilibrium solubility of calcium octadecanoate (or calcium stearate) was measured as a function of pH as well as chelating agent (ethylenediaminetetraacetate disodium salt) and surfactant concentrations. Anionic, nonionic, and amphoteric surfactants were studied. The highest soap scum solubility was observed at high pH with an amphoteric surfactant. Under this condition, the chelant effectively binds calcium, and the stearate anion forms mixed micelles well with the amphoteric surfactant, which is in zwitterionic form at high pH.

This chapter reviews the wide range of colloidal systems amenable to investigation by FT -IR spectroscopy. Molecular level information about the interactions of amphiphilic substances in aggregates such as micelles, bilayers, and gels can be obtained and related to the appearance and stability of the various phases exhibited. The interactions of polymers, surfactants and proteins with interfaces, which substantially modify the solid -liquid or liquid -air interface in many important industrial and natural processes, can also be monitored using FT -IR.Several themes of the application of FT-IR to studies of colloidal particles and interfaces have appeared over the last decade or so. The purpose of this chapter is to attempt to draw together examples of such research topics for both the practicing spectroscopist and workers in the field of colloid and surfactant science. Major advances have been made in recent years in the areas of spectroscopic data handling (which have affected the "look" and "feel" of the analytical laboratory in general) and sample handling (various new optical accessories). These advances have made FT-IR a truly accessible technique, with tremendous potential for application to research in areas of considerable economic, as well as fundamental, importance.Synthetic surfactants are ubiquitous in the modem world, appearing in a wide variety of consumer cleaning products, in foods and cosmetics, and in industrial products and processes such as metal cleaning and enhanced oil recovery. The design of novel surfactant -based products or processes featuring "improved" performance or decreased environmental impact requires an understanding of the relationship of molecular structure to surfactant phase behavior. In the case of "natural amphiphiles" such as the phospholipids, a single phase, the bilayer, is of paramount importance. Significant advances in the understanding of the molecular forces which stabilize these aggregates have been made recently using vibrational spectroscopy. In nature, membrane bilayers incorporate significant amounts of additional substances such as proteins and cholesterol. Although more complex, such systems are also beginning to yield to spectroscopic analysis. Besides being of fundamental interest, membrane bilayer chemistry affects areas of considerable economic opportunity, considering pharmaceutical chemistry alone.Many of the spectroscopic concepts developed in studies of bilayers are applicable to other molecular aggregates such as surfactant miceUes and gels. The