Variation in degree of counterion binding to cesium perfluorooctanoate micelles with surfactant concentration studied by 133Cs and 19F NMR

The concentration dependences of Cs-133 and F-19 chemical shifts for aqueous solutions of cesium perfluorooctanoate are analyzed by using a two-state model to ascertain the results in our previous study on the same system which demonstrates micellar growth along two dimensions based on the analysis of small-angle X-ray and neutron scattering. The distribution of counterions has also been calculated by using a cell model combined with the Poisson-Boltzmann equation. The results are consistent with the increase in the degree of counterion binding with increasing surfactant concentration, which may be related to the two-dimensional growth of micelles.