A NEW OFF-LATTICE MONTE-CARLO MODEL FOR POLYMERS - A COMPARISON OF STATIC AND DYNAMIC PROPERTIES WITH THE BOND-FLUCTUATION MODEL AND APPLICATION TO RANDOM-MEDIA

A model for a multichain polymer system in three-dimensional continuous space is studied by link cell Monte Carlo methods, using systems up to chain length N = 64 and up to 16 384 monomers. The chains consist of beads with a hard core connected by rather stiff harmonic bonds, with a repulsive Lennard-Jones-type interaction between beads chosen such that chains cannot cross each other during their random motions. On RISC workstations the model performs only about a factor of 4 slower than the bond fluctuation lattice model, the qualitative behavior of the time-dependent mean-square displacements and relaxation functions being rather similar to the latter. For the model without obstacles, it is shown that the present continuum model can be approximately mapped on the lattice bond fluctuation model by a suitable rescaling of chain length and volume fraction. But the distinctive advantage of the present model is that it can be applied easily to random media (described by randomly placed rigid obstacles), without the severe ergodicity problems (locked-in configurations) arising in lattice models for such systems. It is shown that static properties of the chains stay nearly unaffected by the obstacles, while the chain motions are considerably slowed down in this frozen environment.