Molecular Simulation of the Phase Behaviour of Attractive Polymers

Through a hierarchical modeling scheme, we determine a phase diagram of attractive, fully flexible and rod-like polymer chains in two and three dimensions. All systems are generated, equilibrated and successively analyzed through the Simu-D software. A surprisingly rich collection of distinct crystal polymorphs appears, which can be finely tuned through the range of attraction and chain stiffness. In three dimensions these include the face centered cubic, hexagonal close packed, simple hexagonal and body centered cubic crystals and the Frank-Kasper phase. A simple geometric model is proposed, based on the concept of cumulative neighbours of ideal crystals, which can accurately predict most of the observed structures and the corresponding transitions. A geometrical analysis is provided on the characteristics of the self-assembled polymer clusters and crystals under conditions that correspond to vacuum. The present work demonstrates, at a fundamental level and by utilizing highly idealized model, how proper fine tuning of selected parameters can be used for the design of polymer crystals with tailored morphologies and structural characteristics.