Brownian dynamics simulation of a spherical particle in charged gel modeled as cubic lattice

Self-diffusion of a tracer particle in an electrically non-charged and charged cubic lattice with the hard-body type excluded-volume effect as a simplified structure of cross-linked network of gel is investigated by Brownian dynamics simulation. Both the excluded-volume and the electrostatic attractive interaction acting between the tracer particle and the cubic lattice result in the reduction in the self-diffusion coefficient as compared to that for the free diffusion. Reduction caused by the electrostatic attractive interaction is significant when d(p)/d(lattice)much less than1 and d(p)/d(lattice)similar to1, where d(lattice) and d(p) denote the mesh size of the cubic lattice and diameter of the tracer particle, respectively. When d(p)/d(lattice)much less than1, the reduction in the self-diffusion coefficient is mainly due to entrapment around the charged points on the cubic lattice located at the middle point of arbitrary two neighboring cross positions. When d(p)/d(lattice)similar to1, the entrapment time in the unit cubic lattice space is greatly enhanced due to the high potential to be overcome when the tracer particle undergoes the translation beyond the boundary of arbitrary two neighboring unit cubic lattices.