Formation of Ionomer Microparticles via Polyelectrolyte Complexation

Developing strategies for assembling ionic polymers into nanoaggregates with desired properties confers effective routes for the fabrications of functional materials. In dilute aqueous solutions, ionomers (composed of a hydrophobic backbone chain and grafted anionic pendant segments) normally self-assemble into small and dispersed clusters due to the electrostatic repulsions. Using coarse-grained molecular dynamics simulations, we develop a simple, convenient, but novel approach for fabricating large ionomer microparticles in dilute aqueous solutions. We demonstrate that added cationic polyelectrolytes (PEs) could electrostatically bind the dispersed ionomers and trigger their self-assembly into microparticles composed of a hydrophobic core and an anionic shell. The size of the microparticles could be precisely controlled by adjusting the concentration and chain length of the binding PEs. Furthermore, bare microparticles can be obtained through PE desorption in saline solution. We examine the mechanical and thermodynamic stability of the ionomer microparticle and its shape-memory nature in response to external force and temperature. Moreover, our simulations on electrophoresis reveal that a mobility reversal of the microparticles occurs due to overcharging of the binding PE. This work contributes to the development of novel strategies to fabricate smart polymer aggregates with predesigned structures and functions.