On the swelling and elastic properties of highly charged polyelectrolyte networks

The end-to-end vector distribution function of a semiflexible chain with an arbitrary persistence length is given in a simple analytical form. The explicit representation of the distribution function enables evaluation of the free energy of a highly charged network as a backbone of the gel where the electrostatic repulsive forces between charged groups increase not only the excluded Volume but also the persistence length. The newly obtained free energy elucidates that the ionic swelling of highly charged gels is mainly due to the presence of the electrostatic persistence length unlike weakly charged ones where the electrostatic excluded volume effect plays an important role. This picture also explains the recently observed ionic dependence of the swelling degree and the elastic modulus.