Concentration and size dependence of dielectric strength and dielectric relaxation of polymers in solutions of a Theta solvent via molecular dynamicssimulations

We consider the dielectric strength and dielectric relaxation of dilute and semidilute solutions of polymers in a Theta solvent. A molecular dynamics technique is employed and the simulation results are contrasted with dielec tric spectroscopy measurements, providing an insight into the molecular fac tors that affect the experimental behavior. The relation between the dielec tric strength and the end-to-end distance of the chains, used in experiment s to determine polymer dimensions, is established via equilibrium and noneq uilibrium simulations. The dielectric loss spectra are computed from the en d-to-end vector autocorrelation function of the simulated systems. At infin ite dilution the simulation spectra conform well with the Rouse model predi ction. The spectra broaden with increasing concentration, and a normal-mode analysis suggests that the overlapping of the chains leads to a broader di stribution of relaxation times. Finally, normal mode relaxation times are f ound to be exponential in density.