Solution Behavior of the Zwitterionic Surfactant Octadecyldimethylbetaine

A light scattering, viscosity, surface tension, and cryo-TEM study was performed on aqueous solutions of octadecyldimethylbetaine (C 18 DMB). The dilute to semidilute crossover concentration was found to be approximately 0.35% concentration by weight from both light scattering and viscosity data. The results from the dynamic light scattering data were significantly better described by a model with two decay times, rather than a single decay, cumulants model. The dynamic light scattering data were also fit to a Kohlrausch−Williams−Watts form, which is consistent with translational diffusion and internal modes. The light scattering, viscosity, and cryo-TEM data are all consistent with the existence of long rodlike micelles. The critical micellar concentration, cmc, was determined via surface tension measurements and found to be 5 × 10 -6 M at 40 °C.