Mesoscale hydrodynamic simulation of short polyelectrolytes in electric fields.

The dynamical, conformational, and transport properties of short flexible polyelectrolytes are studied in salt-free solution under the influence of an external electric field taking hydrodynamic interactions into account. A coarse-grained polymer model is applied and the multiparticle collision dynamics approach is adopted to account for the solvent. We consider various Coulomb interaction strengths and polymer lengths. The scaling behavior of the diffusion coefficient with respect to polymer length strongly depends on the charge interaction strength due to changes in the polyelectrolyte conformations by counterion condensation. The diffusion coefficients at weak Coulomb interaction strengths can well be described by the expression of rodlike objects, whereas at stronger electrostatic interactions, we observe a Zimm-like behavior. The polyelectrolyte mobilities obey the Nernst-Einstein relation at weak charge interactions. For large interaction strengths and long polymers, the mobilities are independent of molecular weight because of the screening of the intramolecular Coulomb interactions by counterions. Our studies demonstrated that the dynamics of polyelectrolytes in dilute solution and in an external field is governed by an interplay of hydrodynamic interactions and counterion condensation.