MONTE-CARLO SIMULATIONS OF THE ORIENTATIONAL ORDER IN A STRAINED POLYMER NETWORK - EFFECT OF DENSITY

Monte Carlo simulations are performed to investigate the uniaxial orde ring of chain segments induced upon stretching a polymer network. The polymer network is modeled by chains with fixed extremities on a cubic lattice. Segmental interactions are introduced by imposing excluded v olume between all segments in the system. A uniaxial contribution to o rientation is shown to arise upon stretching even at a relatively low fraction of occupied sites Phi. This uniaxial contribution is studied as a function of Phi. The variation versus Phi is in agreement with th at observed experimentally in a previous NMR work and is well describe d by a mean field model including orientation-dependent interactions b etween segments. It is shown additionally that a purely entropic model , including the packing entropy of segments, gives a mean field behavi or qualitatively similar to that observed herein.