Direct Measurement of Counterion Distribution around Cylindrical Micelles by Small-Angle X-Ray Scattering

Small-angle x-ray scattering was used to measure the distribution of ${\mathrm{Cs}}^{+}$ counterions around the surface of cylindrical micelles. The scattering intensity distribution was compared with that calculated by use of the analytical solutions of a nonlinear Poisson-Boltzmann (PB) equation in a cell model. Quantitative agreement was obtained for the cases without added salt. The addition of other monovalent salts did not modify the counterion distribution significantly in accordance with the prediction of the numerical solution of the PB equation.