Order-disorder phase transition of polymer systems

Abstract

Evidence is given that dense systems of finite semiflexible polymer chains confined to a lattice do not exhibit at any temperature a long-ranged orientationally ordered state where all chains are parallel oriented. No phase transition is observed. This is shown by simulating various systems at concentrations > 0.95 on the square and cubic lattice with chain lengths of 10 and 20. The overall orientational orderparameter is less than 0.1 for all temperatures, whereas the configurational orderparameter characterizing the flexibility of the chains exhibit a continuous transition corresponding to a transition of each individual chain between its random configuration and a rodlike configuration at low temperatures. Locally there exist orientationally ordered regions having a correlation length of the order of the chain length. From our results we generally suggest that for finite chain lengths, the ground state of a dense system of semiflexible lattice chains is highly degenerated with nonvanishing entropy. Some evidence is given that this degeneracy is removed and accompanied by a genuine phase transition between a disordered and a long-ranged orientationally ordered state if intermolecular interactions are included.