METHODS OF GENERATING DENSE RELAXED AMORPHOUS POLYMER SAMPLES FOR USE IN DYNAMIC SIMULATIONS

A comparison is made between different methods of generating relaxed dense amorphous systems of model linear polymer chains. One of these, referred to as phantom chain growth (PCG), has many advantages when compared with self-avoiding random walk procedures. In PCG chains are grown under non-excluded volume conditions such that successive torsion angles in a chain occur with a probability which is related to immediately adjacent torsion angles only. Van der Waals potentials are then introduced, and the structures are dynamically relaxed using loose-coupling, constant-pressure molecular dynamics. We report a series of experiments on a polyethylene-like polymer designed to test the effect of preparational history and heat treatment on the relaxation of the amorphous samples. It is shown that at 500 K a preparational history dependence can be detected but this can be removed using heat treatment. At lower temperatures, below the glass transition temperature, major difficulties are encountered in observing universal behavior.