Abstract
Counterion distributions around-like polyelectrolytes in solution are measured directly using small-angle rod-like x-ray scattering (SAXS). Two systems are studied: cylindrical micelles formed by a comb-shaped copolymer poly-(1-octadecene-co-maleic anhydride) (PODMA), neutralized by CsOH, in aqueous solution; and 500 Å persistence length DNA fragments in aqueous solution having Na+ or Cs+ as counterions, respectively. Method of SAXS data analysis is presented. The Poisson-Boltzmann (P-B) equation in the cell model is used to compute the counterion distributions. Comparison of SAXS data for the PODMA case with the theory shows that the P-B solution overestimates the charge accumulation on the micellar surface due to the very high linear charge density parameter ζ (= 33) of the micelle, while for the case of CsDNA one needs to assume a considerable amount of counterions present in the major and minor grooves of the double helices.Key wordsPolyelectrolytesPoisson-Boltzmann equationx-ray scattering
Published Version
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