Structure/performance relationships in long chain dimethylamine oxide/sodium dodecylsulfate surfactant mixtures

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.