Strongly Stretched Semiflexible Extensible Polyelectrolytes and DNA

Abstract

The stretching response of a single charged semiflexible and extensible polymer in the limit of large tensile forces is calculated. We consider the effects of (i) the coupling of bending and elongational fluctuations, (ii) the electrostatic contribution to the bending and elongational energies, and (iii) nonlinear bare elastic elongational energies. We show that the electrostatic repulsion between charged monomers leads to an intrinsic stretching force, which cannot be neglected for low salt concentrations. For DNA this effect shifts the B-DNA−S-DNA transition to lower external forces as the salt concentration is decreased, in agreement with experiments. Because of the scale dependence of the electrostatic contribution to the persistence length, the effective persistence length (obtained from fitting the high-force stretching response to a semiflexible chain model) acquires a force dependence which follows a universal heuristic scaling function. As a consequence, flexible (synthetic) polyelectrolytes are ...