Morphologies of spherical bidisperse polyelectrolyte brushes in the presence of trivalent counterions

Abstract

We study surface morphologies of a bimodal polyelectrolyte brush grafted onto a surface of spherical colloid in the presence of trivalent counterions, using molecular dynamics simulations. Both the good and poor solvent conditions are considered. Grafting density and charge fraction are varied to generate a series of microphase separated structures, which represents the competition between the excluded volume interaction and trivalent counterion mediated bridging. The short chains are more extended than the long counterparts under good solvent conditions, which are different with those under poor solvent conditions through a careful analysis on shape factor of grafted chains as well as distributions of monomers and counterions. Furthermore, the electrostatic bridging effect of trivalent counterions is analyzed carefully by classifying them into four states. Also, our simulation results can sever as a guide for improving the performance of polydisperse polyelectrolyte brushes as smart stimuli-responsive materials.