On closed-loop liquid–liquid immiscibility

Abstract

This paper is a contribution to the discussion about the existence of closed liquid–liquid immiscibilities in binary fluid mixtures. In order to complete the picture of closed loops in isotropic fluid mixtures additional global phase diagrams have been calculated. The microscopic effects which cause the closed-loop behaviour are discussed for isotropic model fluids and compared to the effects causing closed loops in systems with strong directional attractive forces. It is concluded that the responsible effects are the same in isotropic and anisotropic systems. The effects differ only in the strength depending on the kind of underlying interaction. The directional attractive forces such as hydrogen bonding are stronger than an isotropic van der Waals attraction. For weak interacting isotropic fluids the closed-loop behaviour turns out to be more sensitive to the chosen equation of state terms.