，成果详细信息-凯发网

two-dimensional simple shear flow of a self-avoiding macromolecular chain is simulated by a lattice monte carlo (mc) method with a pseudo-potential describing the flow field. the simulated velocity profile satisfies the requirements of simple shear flow unless the shear rate is unreasonably high. some diffusion problems for a free-draining bead-spring chain with excluded volume interaction are then investigated at low and relatively high shear rates. three diffusion coefficients are defined and examined in this paper: the conventional self-diffusivity in zero field, dself, the apparent self-diffusivity in flow field, dapp, and the flow diffusivity in simulation, dflow reflecting actually the transport coefficient. it is found that these three diffusivities for a flexible chain are different from each other. what is more important is that self-diffusion exhibits a high anisotropy in the flow field. the apparent self-diffusion along the flow direction is enhanced to a large extent. it is increased monotonically with the increase of shear time or shear strain, whereas the chain configuration can achieve a stationary anisotropic distribution following an interesting overshoot of the coil shape and size. besides a single self-avoiding chain, an isolated brownian bead and a group of self-avoiding beads with a quasi-gaussian spatial distribution are also simulated. according to the comparison, the effects of the connectivity of the chain on the diffusion behavior are revealed. some scaling relations of dapp versus t are consistent with the theoretical analyses in the pertinent literature.