Brownian dynamics simulation of tracer diffusion in a cross-linked network

Brownian dynamics simulation is employed to study the self-diffusion of tracer particles in a cross-linked gel network based on a coarse-grained bead-spring lattice model. Several effects are investigated including the network porosity, flexibility, degree of cross linking, and electrostatic interaction. For uncharged systems, the tracer long-time diffusivity is found to decrease with deceasing porosity and flexibility, but with increasing degree of cross linking. For charged systems, the diffusion is further hindered by the electrostatic interaction, regardless of whether the tracer particle and the network are oppositely or similarly charged. However, there exists a difference in the hindrance mechanism between the two cases. For the former, a substantial decrease in the diffusivity can occur at high network porosities due to electrostatic entrapment.