MEASUREMENT AND INTERPRETATION OF COUNTERION DISTRIBUTIONS AROUND CYLINDRICAL MICELLES

Radial distributions of heavy monovalent counterions around cylindrical micelles are measured directly using a small angle x-ray scattering. For the purpose of the analysis, the shape and size of the micelles are determined separately by a small angle neutron scattering. The micelles we used are formed by a comb-shaped copolymer poly-(1-octadecene-co-maleic anhydride), abbreviated as PODMA in aqueous solutions neutralized by cesium hydro-oxides. The results are used to critically test the validity of solutions of non-linear Poisson-Boltzmann (PB) equation in the cell model to predict the radial distributions of monovalent counterions. The accuracy of the solutions of the non-lineaar PB equation for different magnitudes of linear charge density parameter is checked against Monte Carlo simulations. For comparison, we also show results of a similar experiment and analysis done for the counterion distributions around persistent length DNA in solution.