MONTE-CARLO SIMULATION OF POLYMER-CHAIN COLLAPSE IN ATHERMAL SOLVENTS

By computer simulation, Dijkstra et al. [M. Dijkstra, D. Frenkel, and J. P. Hansen, J. Chem. Phys. 101, 3179 (1994)] reported the first entr opy-driven polymer chain collapse in an athermal solvent. To gain a be tter understanding of chain collapse physics in the absence of attract ive interactions, we performed on-lattice NVT Monte Carlo simulations on a single polymer chain immersed in a hard-core solvent of variable size, shape, and density. In general, solvent quality decreases with i ncreasing solvent density and incipient chain collapse occurs at a uni que critical density for a given solvent size and shape. The critical density is smaller for large solvent molecules, but solvent shape also plays a role. Unfavorable solvent-chain excluded volume (EV) interact ions drive the collapse transition. The EV interaction is reduced and the solvent entropy increases when the chain collapses, but there is a n accompanying and unfavorable loss of chain conformational entropy. A t the transition density these opposing entropy changes are comparable in magnitude. In the special and important case where the EV interact ion is chain conformation independent, no collapse is observed at any solvent density. (C) 1996 American Institute of Physics.