Europhys. Lett.
Volume 67, Number 2, July 2004
Page(s) 219 - 225
Section Interdisciplinary physics and related areas of science and technology
Published online 01 July 2004
Europhys. Lett., 67 (2) , pp. 219-225 (2004)
DOI: 10.1209/epl/i2004-10064-2

Phase equilibria and fractionation in a polydisperse fluid

N. B. Wilding1 and P. Sollich2

1  Department of Physics, University of Bath - Bath BA2 7AY, UK
2  Department of Mathematics, King's College London - Strand London WC2R 2LS, UK

(Received 17 March 2004; accepted in final form 11 May 2004)

We describe how Monte Carlo simulation within the grand canonical ensemble can be applied to the study of phase behaviour in polydisperse fluids. Attention is focused on the case of fixed polydispersity in which the form of the "parent" density distribution $\rho^{\circ}(\sigma)$ of the polydisperse attribute $\sigma$ is prescribed. Recently proposed computational methods facilitate determination of the chemical potential distribution conjugate to $\rho^{\circ}(\sigma)$. By additionally incorporating extended sampling techniques within this approach, the compositions of coexisting ("daughter") phases can be obtained and fractionation effects quantified. As a case study, we investigate the liquid-vapor phase equilibria of a size-disperse Lennard-Jones fluid exhibiting a large ( $\delta=40\%$) degree of polydispersity. Cloud and shadow curves are obtained, the latter of which exhibit considerable fractionation with respect to the parent. Additionally, we observe a surprisingly large degree of broadening of the coexistence region relative to the monodisperse limit.

64.70.Fx - Liquid-vapor transitions.
61.20.Ja - Computer simulation of liquid structure.
68.35.Rh - Phase transitions and critical phenomena.

© EDP Sciences 2004