Conformation of a natural polyelectrolyte in semidilute solutions with no added salt

Abstract

This manuscript embodies a comprehensive study of the conformation of a model polyelectrolyte, alginate, in solutions with no added salt. Despite extensive theoretical investigations in this field, there are only few experimental small angle scattering studies aimed at corroborating the proposed theories. Small angle X-ray scattering plots were analyzed by modeling the full q dependence. Three models were examined as a way to represent the scattering from a single chain: a model of a worm-like chain, a model of a semiflexible chain without excluded volume effects, and a model of a semiflexible chain with excluded volume effects. The electrostatic interactions between chains were accounted for by using two models. We found that incorporating a Gaussian function to the polymer version of the reference interaction site model (PRISM) has led to a good description of the experimental data. This model has not been fitted to experimental scattering from polyelectrolytes yet. Modeling the complete scattering curve allowed us to deduce information which was not available before for alginate. In particular, we found that the persistence length is not correlated with the chemical composition of the alginate. However, the electrostatic correlation length increases with the G-content. The dependence of the persistence length on the concentration was found to comply with the Odjik–Skolnick–Fixman (OSF) theory, where the persistence length l depends on the square of the debye length l ∝ κ⁻².