ζ-Potentials of Natural and Synthetic Fibers in SDS Solutions and the Viscosity of SDS Solutions above the Critical Micelle Concentration

Abstract

Abstract In order to investigate the adsorption behavior of an anionic surfactant on fibers, the ζ-potentials of natural and synthetic fibers in aqueous solutions of sodium dodecyl sulfate (SDS), mainly above the critical micelle concentration (CMC), were measured. Further, the change in the structure of the SDS micelle in aqueous solutions was studied by means of the viscosity method. At first the reduced viscosity for the SDS micelle, ηspm/cm (cm: the micellar concentration), increased rapidly with the cm as long as the cm was small; thereafter, after a break, it approximated the saturated values as a whole. The results calculated from the experimental data using Jones and Dole’s equation showed two distinct breaks. The first break corresponded to the 1st CMC, and the second, nearly to the break in the ηspm/cm vs. cm curve. In addition, the intrinsic viscosity for the SDS micelle, [η]M, and the effective specific volume, V, were obtained. From these results, it can be assumed that the structure of the SDS micelle is variable at the break in the ηspm/cm vs. cm curve. The ζ-potentials of fibers in aqueous SDS solutions changed rapidly with an increase in the concentration of SDS, but they remained approximately constant in the vicinity of the CMC. At much higher concentrations above the CMC (in the vicinity of the SDS concentration of 2×10−2 mol/l), the ζ values again gradually changed; thereafter, after a break, they became nearly constant again. The change in the ζ-potentials corresponds approximately to the break in the ηspm/cm vs. cm curve. Therefore, it may be suggested that it is connected with the change in the structure of the SDS micelle.