Demixing and orientational ordering in mixtures of rectangular particles

Abstract

Using scaled-particle theory for binary mixtures of two-dimensional hard particles with rotational freedom, we analyse the stability of nematic phases and the demixing phase behaviour of a variety of mixtures, focussing on cases where at least one of the components consists of hard rectangles or hard squares. A pure fluid of hard rectangles may exhibit, aside from the usual uniaxial nematic phase, an additional (tetratic) oriented phase, possessing two directors, which is the analogue of the biaxial or cubatic phases in three- dimensional fluids. There is computer simulation evidence that the tetratic phase might be stable with respect to phases with spatial order for rectangles with low aspect ratios. As hard rectangles are mixed with other particles not possessing stable tetratic order by themselves, the tetratic phase is destabilised, via a first- or second-order phase transition, to uniaxial nematic or isotropic phases; for hard rectangles of low aspect ratio tetratic order persists in a relatively large range of volume fractions. The order of these transitions depends on the particle geometry, dimensions and thermodynamic conditions of the mixture. The second component of the mixture has been chosen to be hard discs or disco-rectangles, the geometry of which is different from that of rectangles, leading to packing frustration and demixing behaviour, or simply rectangles of different aspect ratio. These mixtures may be good candidates for observing thermodynamically stable tetratic phases in monolayers of hard particles. Finally, demixing between fluid (isotropic--tetratic or tetratic--tetratic) phases is seen to occur in mixtures of hard squares of different sizes when the size ratio is sufficiently large.

27 pages, 9 figures

References in corpus (12)

• Tetratic Order in the Phase Behavior of a Hard-Rectangle System
• Nonequilibrium steady states in a vibrated-rod monolayer: tetratic, nematic and smectic correlations
• Fluid mixtures of parallel hard cubes
• Nematic phase transitions in mixtures of thin and thick colloidal rods
• Isotropic-Nematic transition of long thin hard spherocylinders confined in a quasi-two-dimensional planar geometry
• Effect of particle geometry on phase transitions in two-dimensional liquid crystals
• Orientational ordering in hard rectangles: The role of three-body correlations
• Fundamental measure theory for mixtures of parallel hard cubes. II. Phase behavior of the one-component fluid and of the binary mixture
• Capillary ordering and layering transitions in two-dimensional hard-rod fluids
• Phase Separation in Two-Dimensional Additive Mixture
• Demixing behavior in two-dimensional mixtures of anisotropic hard bodies
• Stability of smectic phases in hard-rod mixtures

Cited by in corpus (12)

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• Domain walls in two-dimensional nematics confined in a small circular cavity
• Two-dimensional nematics in bulk and confined geometries
• Sedimentation stacking diagram of binary colloidal mixtures and bulk phases in the plane of chemical potentials
• Uniform phases in fluids of hard isosceles triangles: one component and binary mixtures
• Phase behavior of mixtures of hard ellipses: A scaled particle density functional study
• Demixing and tetratic ordering in some binary mixtures of hard superellipses
• Role of length-polydispersity on the phase behavior of freely-rotating hard-rectangle fluid
• Three stable phases and thermodynamic anomaly in a binary mixture of hard particles
• Thermodynamic behavior of binary mixtures of hard spheres: Semianalytical solutions on a Husimi lattice built with cubes
• Fluid-fluid versus fluid-solid demixing in mixtures of parallel hard hypercubes
• Fluid-fluid demixing and density anomaly in a ternary mixture of hard spheres