Anomalous structure and scaling of ring polymer brushes

A comparative simulation study of polymer brushes formed by grafting at a planar surface either flexible linear polymers (chain length N-L) or (non-catenated) ring polymers (chain length N-R = 2N(L)) is presented. Two distinct off-lattice models are studied, one by Monte Carlo methods, the other by molecular dynamics, using a fast implementation on graphics processing units (GPUs). It is shown that the monomer density profiles rho(z) in the z-direction perpendicular to the surface for rings and linear chains are practically identical, rho(R)(2N(L), z) = rho(L)(N-L, z). The same applies to the pressure, exerted on a piston at height z, as well. While the gyration radii components of rings and chains in the z-direction coincide, too, and increase linearly with N-L, the transverse components differ, even with respect to their scaling properties: R-gxy((L)) proportional to N-L(1/2), R-gxy((R)) proportional to N-L(0.4). These properties are interpreted in terms of the statistical properties known for ring polymers in dense melts. Copyright (C) EPLA, 2011