A Generic Model for Growth and Morphogenesis of Polymer Crystals in Two Dimensions

Abstract

We discuss a generic algorithm to simulate the growth of chain crystals from adsorbed monolayers. Chains are considered as elementary statistical units which can exist in states of different internal order. Non-equilibrium growth is combined with internal reorganization processes with a tendencyto improve the crystalline order towards the fully stretched chain state. The thickness of the grown crystals is selforganized as a result of the interplay between a barrier to increase local chain order and the gain of enthalpyb yaccessing higher degrees of order (longer stems). When the reservoir of liquid chains is exhausted relaxation processes dominate. Since chains located at the crystal rims have a higher mobility they are prone to spontaneous reorganization into higher ordered state. This results in striking and very stable morphological phases such as overgrown rims or hole-rim patterns. Increasing the temperature yields to further morphogenesis. In particular droplet-like patterns can be obtained which show liquid-like features on large scales but are made up of highly ordered crystalline chains. We argue that final melting of polymer crystals is not related to the structure which is crystallized but only to the descendants in the morphogenesis of the chain crystal.

This might be different for copolymers, where an equilibrium between the stretching of the amorphous block at the expense of folding or tilting of the crystalline block is conceivable