UNIAXIALITY INDUCED IN A STRAINED POLYMER NETWORK - THEORY AND MONTE-CARLO SIMULATIONS

Deuterium nuclear magnetic resonance experiments on rubber networks un der uniaxial stress display a characteristic feature: A doublet struct ure for network chains and for free chains diffusing in the network. T he doublet structure can be explained in a mean field theory by introd ucing orientational segmental interactions in the network system. A me an field theory of this kind is explicitly developed for a network sys tem on a cubic lattice. Monte Carlo simulations on a cubic lattice are performed and compared to theory. Segmental interactions are simply i ntroduced by applying the concept of mutually and self-avoiding chains in the simulation. It is confirmed that the segmental interactions in troduce a uniaxial segmental orientation in the sense that each segmen t shows an orientational behavior as being under the influence of a un iaxial external field. The mean field theory is shown to be well repro duced by the simulations. The calculation of the nuclear magnetic reso nance spectrum for the model network of the simulation gives a doublet structure only for the case where steric interactions are present.