Molecular Simulation of Salt Ion Effect on Anionic Polyelectrolyte Chain

The effect of salt ions on anionic polyelectrolyte chain structure has been studied by molecular mechanics and molecular dynamics, and the reason for sedimentation of the anionic polyelectrolyte in the salt solution is explored. Considering sodium polyacrylate as a model compound of anionic polyelectrolytes, the conformation of polyacrylate in salt-free and CaCl₂ solution is studied. The simulation results showed that anionic polyelectrolytes in aqueous solution had an extended chain structure due to the role of strong electrostatic repulsion. After introduction of Ca²⁺ to the solution, the collapse of the anionic polyelectrolyte chain happens. By analysis of the radius of gyration and the radial distribution function, the basic reason for the collapse of anionic polyelectrolyte chains in salt solution is clarified with atomistic resolution.