Morphological variation in a collapsed single homopolymer chain

We studied the thermodynamics in a single homopolymer chain using a multicanonical Monte Carlo simulation. A polymer chain that exhibits an elongated coli state in a good solvent, or at high temperatures, collapses into a condensed state, i.e., coli-globule transition. For flexible polymer chains, as the temperature decreases, the coli state changes into a liquidlike spherical globule, and this liquid state then changes into a solidlike spherical globule; these are similar to the transitions between gas and liquid and between liquid and solid, respectively. For stiff polymer chains, the coli state changes into a crystalline state without the appearance of an intermediate liquidlike state, to give a product with toroidal morphology. For chains intermediate between stiff and flexible, the coli state changes into a state in which toroid and rod shapes coexist, and this state changes into a single solidlike state in which only the rod shape is present. These calculational results correspond well to experimental findings for the products of the collapse of single long DNA chains. (C) 1998 American Institute of Physics.