What Happens When Threading is Suppressed in Blends of Ring and Linear Polymers?

Self-diffusivity of a large tracer ring polymer, Dr, immersed in a matrix of linear polymers with Nl monomers each shows unusual length dependence. Dr initially increases, and then decreases with increasing Nl. To understand the relationship between the nonmonotonic variation in Dr and threading by matrix chains, we perform equilibrium Monte Carlo simulations of ring-linear blends in which the uncrossability of ring and linear polymer contours is switched on (non-crossing), or artificially turned off (crossing). The Dr ≈ 6.2× 10−7N2/3 l obtained from the crossing simulations, provides an upper bound for the Dr obtained for the regular, non-crossing simulations. The center-of-mass mean-squared displacement (g3(t)) curves for the crossing simulations are consistent with the Rouse model; we find g3(t) = 6Drt. Analysis of the polymer structure indicates that the smaller matrix chains are able to infiltrate the space occupied by the ring probe more effectively, which is dynamically manifested as a larger frictional drag per ring monomer.