title: Effect of polydispersity on diffusion in random obstacle matrices.
abstract: The dynamics of tracers in disordered matrices is of interest in a number of diverse areas of physics such as the biophysics of crowding in cells and cell membranes, and the diffusion of fluids in porous media. To a good approximation the matrices can be modeled as a collection of spatially frozen particles. In this Letter, we consider the effect of polydispersity (in size) of the matrix particles on the dynamics of tracers. We study a two dimensional system of hard disks diffusing in a sea of hard disk obstacles, for different values of the polydispersity of the matrix. We find that for a given average size and area fraction, the diffusion of tracers is very sensitive to the polydispersity. We calculate the pore percolation threshold using Apollonius diagrams. The diffusion constant, D, follows a scaling relation D~(φ(c)-φ(m))(μ-β) for all values of the polydispersity, where φ(m) is the area fraction and φ(c) is the value of φ(m) at the percolation threshold.
authors.affiliation: Department of Chemistry, Sogang University, Seoul, Republic of Korea.
authors.forename: Hyun Woo
authors.initials: HW
authors.lastname: Cho
authors.forename: Gyemin
authors.initials: G
authors.lastname: Kwon
authors.forename: Bong June
authors.initials: BJ
authors.lastname: Sung
authors.forename: Arun
authors.initials: A
authors.lastname: Yethiraj