Investigations of mechanical properties of polymer brushes and hydrogels through molecular dynamics simulation

In this thesis, the forces between surfaces coated with polyelectrolye brushes and polymer gels were investigated via molecular dynamics simulation on a computer workstation that I built.The first project investigated the reasons for why grafted polyelectrolye brushes have smaller friction coefficients than grafted neutral polymer brushes.The flexible neutral polymer brush is treated as a bead-spring model, and the polyelectrolyte brush is treated the same way except that each bead is charged and there are counterions present to neutralize the charge.We investigated the friction coefficient, monomer density, and brush penetration for the two kinds of brushes with both the same grafting density and the same normal force under good solvent conditions.We found that polyelectrolyte brushes have smaller friction coefficients in both simulations.We present evidence that the reason for this is that the extra normal force contribution provided by the counterion osmotic pressure that exists for polyelectrolyte brushes permits them to support the same load as identical neutral polymer brushes of higher grafting density.Because of the resulting lower monomer density for the charged brushes, fewer monomer collisions take place per unit time, resulting in a lower friction coefficient.The second project investigated interactions between two grafted polymer gels.Unlike polyelectrolyte polymer brushes, polymer chains are linked to other neighboring polymer chains.We studied a defect-free network of C Figure Permission 93