Size, flexibility, and scattering functions of semiflexible polyelectrolytes with excluded volume effects: Monte Carlo simulations and neutron scattering experiments

We present a systematic Monte Carlo study of the scattering function S(q) o f semiflexible polyelectrolytes at infinite dilution, in solutions with dif ferent concentrations of added salt. In the spirit of a theoretical descrip tion of polyelectrolytes in terms of the equivalent parameters, namely, per sistence length and excluded volume interactions, we used a modified wormli ke chain model, in which the monomers are represented by charged hard spher es placed at distance a. The electrostatic interactions are approximated by a Debye-Huckel potential. We show that the scattering function is quantita tively described by that of uncharged wormlike chains with excluded volume effects provided that an electrostatic contribution is added to the persist ence length. In addition we have studied the expansion of the radius of gyr ation and of the end-to-end distance. The results are in agreement with the picture outlined in the Odijk-Skolnick-Fixman theory, in which the behavio r of charged polymers is described only in terms of increasing local rigidi ty and excluded volume effects. Moreover, the Monte Carlo data are found to be in very good agreement with experimental scattering measurements with e quilibrium polyelectrolytes, i.e., giant wormlike micelles formed in mixtur es of nonionic and ionic surfactants in dilute aqueous solution, with added salt.