Charge Inversion of a Spherical/Rod Macroion under Different Coion and Monovalent Salt Conditions: Electrophoresis by Molecular Dynamics Simulations

"By molecular dynamics simulations we study the effects of coion radius and valence and those of monovalent salt on the electrophoretic mobility of a charge-inverted spherical or rod macroion. For the parameter windows examined, the reversed mobility increases with the ratio of coion to counterion radii a^-/a^+, which peaks at a^-/a^+ approx 1.5. It decreases with the ratio of coion to counterion valences Z^-/Z^+, and becomes non-reversed for Z^-/Z^+>1. The monovalent salt suppresses reversed mobility when its ionic strength exceeds that of the adsorbed counterions, except for mobility enhancement of a strongly charged macroion at small salt ionic strength. There is a threshold surface charge densith for charge inversion. Polymers of multivalent counterions (polyelectrolyte) are effective for charge inversion of a weakly charge rod macroion like DNA with the help of large coions.