Thermal maximum in the size of short polyelectrolyte chains. A Monte Carlo study

We present Monte Carlo simulation results for the temperature dependence of the conformation characteristics for an isolated polyelectrolyte chain with counterions immersed in a continuum dielectric. The polyion consists of an ordered set of N identical charged hard spheres with fixed separation. All interactions between the ions are taken to be Coulombic. An interesting temperature dependence is found; for high temperatures the polymer conformation approaches the random coil on increasing the temperature in contrast to the behavior at low temperatures, where we find that the polymer tends to swell with increasing temperature. It is argued that this phenomenon can be understood in terms of the screening effect introduced by Manning condensation of the counterions.