Shear-like Dynamics of Model Complex Coacervates under Electric Fields

High Resolution Image Download MS PowerPoint Slide Complex coacervates are binary mixtures of oppositely charged polyelectrolytes. Their liquid–liquid phase separation is crucial to biological processes and to the design of a wide range of high-tech materials, thanks to its high tunability via temperature, pH, and charge sequence, to name a few. Polyelectrolytes are inherently responsive to electric fields, but while the field-induced behavior of single chains has been widely studied, the response of a dense coacervate phase to electric fields remains largely unknown. We performed coarse-grained molecular dynamics simulations of salt-free coacervates under a constant external electric field. We show that the polyelectrolyte chains extend, tumble, and align in the direction of the field. The radius of gyration components and the tumbling frequency depend on the field strength according to a power law, comparable to that of neutral polymers at varying shear deformation rates. Moreover, the displacement of particles in the direction perpendicular to the field increases with field strength, suggesting a reduction in viscosity characteristic of shear-thinning polymer melts and solutions. For weak electrostatic interactions and high field strength, like-charged particles aggregate into lanes parallel to the field direction to reduce friction─a universal behavior of laning transitions. These results shed light on the rich behavior of coacervates subjected to an electric field and provide another tool to manipulate coacervate material properties.