RHEOLOGY AND STRUCTURAL-CHANGES OF POLYMER MELTS VIA NONEQUILIBRIUM MOLECULAR-DYNAMICS

Results of nonequilibrium molecular dynamics computer simulations of a planar Couette flow are presented for the multibead anharmonic-spring model. The finitely extensible nonlinear elastic force law is used to connect the up to 100 beads of a chain molecule. Rheological data (sh ear viscosity, normal pressure differences) are discussed and compared with quantities describing the chain conformation (e.g., alignment te nsor, static structure factor). This renders possible a test of the th eoretical approaches which connect these quantities. In agreement with recent experiments, the static strucure factor exhibits characteristi c elliptical distortions of the polymer coil whose magnitude depends o n the distance from the gyration center. In our simulations the zero-s hear-rate viscosity is found to scale linearly with the number of bead s N up to chains with N = 60. A weak upturn of the viscosity per bead for N = 100 is found which may indicate the onset of the reptation reg ime.