Highly size-asymmetrical fluid mixtures arise in a variety of physical contexts, notably in suspensions of colloidal particles to which much smaller particles have been added in the form of polymers or nanoparticles. Conventional schemes for simulating models of such systems are hamstrung by the difficulty of relaxing the large species in the presence of the small one. We describe Monte Carlo algorithms capable of tackling this problem and apply them to the problem of determining effective potentials in size asymmetrical hard sphere mixtures, thereby allowing quantitative tests of the predictions of density functional theory. We then introduce recently developed techniques that permit the accurate study of phase behavior and critical phenomena in size asymmetrical mixtures. The methods are applied to study the liquid-vapor phase diagram of a particular mixture of Lennard-Jones particles having a 10:1 size ratio. The results reveal qualitatively different behavior to that expected from the standard depletion picture.
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