(10f) Molecular Dynamics Simulations of the Effect of Dc and AC Electric Field on Polyelectrolyte

Polyelectrolytes are molecules consisting of repeating ionizable groups which dissociate in water or other polar solvents, leaving a charged polymer backbone. A highly ionized polyelectrolyte in solution attracts small mobile counterions of opposite charge, partially screening the backbone charge, and mediating the intermolecular Coulomb repulsion. The difficulty in studying polyelectrolyte-counterions complexes resides in the delicate interplay of the long range electrostatic interactions, short range intermolecular interactions, and thermal energy, all of comparable magnitude. In contrast to previous studies, which considered equilibrium properties of polyelectrolyte-counterions complexes alone, we used molecular dynamics (MD) simulations to study the spatio-temporal dynamics of charge fluctuations around a flexible polyelectrolyte molecule at charge densities above and below the classic counterion condensation threshold. We report the results of MD simulations of the behavior of a polyelectrolyte subject to DC and AC fields. Theoretical predictions are compared with experimental data on electrophoretic mobility, polarization, and birefringence of dilute polyelectrolyte solutions.