TY - JOUR

T1 - Simulation estimates of cloud points of polydisperse fluids

AU - Buzzacchi, Matteo

AU - Sollich, Peter

AU - Wilding, Nigel B.

AU - Müller, Marcus

PY - 2006/4/18

Y1 - 2006/4/18

N2 - We describe two distinct approaches to obtaining the cloud-point densities and coexistence properties of polydisperse fluid mixtures by Monte Carlo simulation within the grand-canonical ensemble. The first method determines the chemical potential distribution μ (σ) (with σ the polydisperse attribute) under the constraint that the ensemble average of the particle density distribution ρ (σ) match a prescribed parent form. Within the region of phase coexistence (delineated by the cloud curve) this leads to a distribution of the fluctuating overall particle density n, p (n), that necessarily has unequal peak weights in order to satisfy a generalized lever rule. A theoretical analysis shows that as a consequence, finite-size corrections to estimates of coexistence properties are power laws in the system size. The second method assigns μ (σ) such that an equal-peak-weight criterion is satisfied for p (n) for all points within the coexistence region. However, since equal volumes of the coexisting phases cannot satisfy the lever rule for the prescribed parent, their relative contributions must be weighted appropriately when determining μ (σ). We show how to ascertain the requisite weight factor operationally. A theoretical analysis of the second method suggests that it leads to finite-size corrections to estimates of coexistence properties which are exponentially small in the system size. The scaling predictions for both methods are tested via Monte Carlo simulations of a polydisperse lattice-gas model near its cloud curve, the results showing excellent quantitative agreement with the theory.

AB - We describe two distinct approaches to obtaining the cloud-point densities and coexistence properties of polydisperse fluid mixtures by Monte Carlo simulation within the grand-canonical ensemble. The first method determines the chemical potential distribution μ (σ) (with σ the polydisperse attribute) under the constraint that the ensemble average of the particle density distribution ρ (σ) match a prescribed parent form. Within the region of phase coexistence (delineated by the cloud curve) this leads to a distribution of the fluctuating overall particle density n, p (n), that necessarily has unequal peak weights in order to satisfy a generalized lever rule. A theoretical analysis shows that as a consequence, finite-size corrections to estimates of coexistence properties are power laws in the system size. The second method assigns μ (σ) such that an equal-peak-weight criterion is satisfied for p (n) for all points within the coexistence region. However, since equal volumes of the coexisting phases cannot satisfy the lever rule for the prescribed parent, their relative contributions must be weighted appropriately when determining μ (σ). We show how to ascertain the requisite weight factor operationally. A theoretical analysis of the second method suggests that it leads to finite-size corrections to estimates of coexistence properties which are exponentially small in the system size. The scaling predictions for both methods are tested via Monte Carlo simulations of a polydisperse lattice-gas model near its cloud curve, the results showing excellent quantitative agreement with the theory.

UR - http://www.scopus.com/inward/record.url?scp=33645708559&partnerID=8YFLogxK

U2 - 10.1103/PhysRevE.73.046110

DO - 10.1103/PhysRevE.73.046110

M3 - Article (Academic Journal)

AN - SCOPUS:33645708559

VL - 73

JO - Physical Review E: Statistical, Nonlinear, and Soft Matter Physics

JF - Physical Review E: Statistical, Nonlinear, and Soft Matter Physics

SN - 1539-3755

IS - 4

M1 - 046110

ER -