Evaporation of Polymer Solutions Containing both Polycations and Polyanions: A Molecular Dynamics Study

Polyelectrolyte solutions show rich physical behavior different from that of solutions of neutral polymers. For example, in a solution of both polycations and polyanions the complexation of oppositely charged chains can lead to complex coacervates that contain most of the two polymers. Such equilibrium phenomena have been studied for many decades. However, other nonequilibrium processes such as the evaporation of polyelectrolyte solutions have received less attention. We use molecular dynamics simulations to study the evaporation of solutions containing both polycations and polyanions. The polymers are represented by MARTINI-type bead-spring chains. Water is used as the solvent and modeled with a model taking into account polarization effects. Counterions and salts are explicitly included as mobile single beads. The effects of polymer concentrations, salt concentrations, and evaporation rates on the structure of the final polymer film are clarified. The connections of the film structure to the complexation behavior of polyelectrolytes prior to evaporation are elucidated. Our results reveal potential new strategies of fabricating polyelectrolyte films with controlled structures.