Solution behavior of the zwitterionic surfactant octadecyldimethylbetaine

A light scattering, viscosity, surface tension, and cryo-TEM study was performed on aqueous solutions of octadecyldimethylbetaine (C18DMB). The dilute to semidilute crossover concentration was found to be approximately 0.35% concentration by weight from bath 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 x 10(-6) M at 40 degrees C.