Monte Carlo simulations of phase equilibria for a lattice homopolymer model

Vapor-liquid phase equilibria for lattice homopolymer systems are simulated in the Gibbs ensemble for chains of length n = 1, 8, 16, 32, 64, and 128 using a newly proposed methodology for volume change moves [Mackie et al., Europhys. Lett. 27, 549 (1994)]. This is the first time that extensions of the Gibbs ensemble methodology for direct calculation of phase coexistence are presented for lattice models. The simulation results show, in agreement with experiment, that the chain length dependence of the critical temperature of polymer-hole systems follows the Schultz-Flory form. The critical densities obey an n ^-0.32 scaling relationship over this limited range in chain lengths, an exponent somewhat less than is found from experimental data. We show that both the Flory model and the Guggenheim theory do not agree with the simulation results, although the Guggenheim model permits better agreement in all cases.