Showing papers by "G. N. Patey published in 2003"

Liquid–vapor criticality in a fluid of charged hard dumbbells

Abstract: The vapor–liquid criticality of a fluid of charged hard dumbbells is investigated employing grand canonical Monte Carlo simulations and mixed-field finite-size scaling methods. The reduced critical temperature and density obtained are Tc*=0.04911±0.00003 and ρc*=0.101±0.003, respectively. The critical temperature is very close to that of the restricted primitive model (RPM) for ionic fluids, while the critical density is ∼25% larger than that of the RPM. The “fits” to the Ising ordering operator distribution are good, and are of similar quality to those found for the RPM with systems of comparable size. However, for the finite-size systems simulated, the constant volume heat capacity, CV, gives no indication of an Ising-type “divergence” at Tc. This is analogous to the RPM, and serves to demonstrate that this still puzzling behavior is not restricted to that model.

Surfactant-stabilized structures in confined liquids

Abstract: Grand canonical Monte Carlo simulations are used to investigate the effect of surfactant on binary Lennard-Jones mixtures confined between planar, chemically patterned surfaces. Near bulk demixing coexistence, confined binary mixtures form liquid “bridges” joining specifically patterned surface areas. The length of these bridges is restricted by the unfavorable liquid–liquid interfacial tension, and in the present paper we show that this constraint can be significantly reduced by adding surfactant to the system. This leads to very extended liquid bridges and to other structures not found in the simple two-component case. We give a qualitative discussion of the surface-surfactant -induced liquid structures and examine in detail the associated forces acting between the plates.

The constant-volume heat capacity of near-critical fluids with long-range interactions: A discussion of different Monte Carlo estimates

Abstract: The constant-volume heat capacities, CV, of various near-critical fluids with long-range potentials have been obtained using both canonical and grand-canonical Monte Carlo (GCMC) calculations. In the case of the restricted primitive model it is shown that the large discrepancies between previously reported results arise from the use of different simulation ensembles. In order to investigate how well the different ensemble estimates of CV obtained with small systems can indicate the universality class of the bulk fluid, calculations have been performed for fluids with attractive pair interactions which vary like −1/ra, with a=6, 4, and 3.1. For a=6, Ising-type criticality is expected, while for a=4 and 3.1 the criticality is mean-field. For each of these models the canonical-ensemble estimates of CV do not provide unambiguous confirmation of the expected critical behavior, and hence this is not a reliable method for determining the universality class. This is also true of the GCMC estimates of CV, which ap...