The Application of the Archibald Ultracentrifugal Method to the Determination of the Micellar Molecular Weight of the Anionic Surface Active Agents

Abstract

Abstract (1) The values of the micellar molecular weight of SDS in water and in a sodium chloride solution could not be obtained by the Archibald method, whereas the observed Mo may represent the relative values, each corresponding to a given instant of centrifugation. However, a CMC could be definitely determined which agreed with the values reported by other workers. As may be noted from the slope of the dependency of M0 on time, the SDS solution is non-ideal above the CMC while it is polydisperse below the CMC. The abnormally high association in the critical micelle region might be caused by the incomplete dissociation of counter ions, accompanied by a change in the equilibrium between the micelle and the free ion of SDS at a given instant of centrifugation. (2) When the electrolyte is absent, β-NF’s presumably exist in a monomeric state, but in a 0.1 m sodium chloride solution they associate, the degree of association being proportional to the x. In the region of 0.25∼1.0% concentration, micelles of β-NF were observed to be polydisperse.