The force-extension behavior of charged polymers is investigated by the means of Monte Carlo simulations in the stress ensemble, strain ensemble and by a method which gives the free energy for a chosen range of end-to-end distances. All three methods are equivalent within statistical limits. To focus on the effects of polymer charge on the force-extension curve, we have studied net-neutral polyampholytes as a function of charge block size and polyelectrolytes with neutralizing counterions of various valences. The force-extension curves of polyampholytes with random charge sequences or small charge block sizes or polyelectrolytes with multivalent counterions are similar to force-extension curves for uncharged polymers. Polyampholytes with large charge block sizes can form pearl-necklace structures which give rise to a plateau in the force-extension curve.
Journal of Physical Chemistry B,
Vol. 107, no. 32 (Aug 2003), pp. 8131-8139
The authors acknowledge support of the Particulate Fluid Processing Centre, a special Research Centre of the Australian Research Council, the Victorian Partnership for Advanced Computing, and the Wenner-Gren Foundations.