Flow driven transitions of polyelectrolytes

Abstract

The nonequilibrium properties of uniformly charged linear polymers in the presence of explicit counterions under shear flow are studied by coarse-grained mesoscale hydrodynamics simulations. The conformational properties of the polyelectrolyte (PE) are quantified by the gyration tensor, the distribution of the end-to-end distance, and alignment with the flow, which display rather universal behavior for small and moderate electrostatic interaction strengths in the regime of condensed counterions. In the limit of strong counterion condensation, shear flow leads to a globule-coil transition and polymer stretching, associated with an increase of the effective PE charge. The polyelectrolytes exhibit a pronounced tumbling motion with cyclic stretched and collapsed conformations. The average tumbling-time period decreases with increasing shear rate by a power-law with the exponent −2/3 for PEs in the coiled state. The tumbling time exhibits a plateaulike regime over nearly a decade of shear rates for PEs in the globular state. In addition, we identify various characteristic PE structures under flow in the globule and coil limits determined by the condensed counterions.