Order-Disorder Transitions in Tetrahedral Lattice Polymer Systems

Monte Carlo simulations were performed on multichain, semiflexible polymer systems with excluded volume confined to a diamond lattice, and the requirements for a phase transition between a globally random and a globally anisotropic phase were explored. For chains composed of n = 12 and 24 beads packed a t volume fractions 0.5 and 0.75, a transition to a globally ordered phase is not observed if the attractive interactions are excluded, in agreement with recent work of Baumgartner (Baumgartner, A. J. Chem. Phys. 1986,84,1905) on square and cubic lattice multichain systems. Inclusion of attractive interactions between nonbonded nearest-neighbor pairs of beads produces an isotropic-to-anisotropic phase transition which is probably first order. The properties of the isotropic and globally ordered phases are extensively characterized, and the ability of simple mean field theory to treat the isotropic-nematic phase transition is examined.