Demixing behavior in two-dimensional mixtures of anisotropic hard bodies

11 pages, 9 figures.-- PACS nrs.: 64.70.Md, 64.75.+g, 61.20.Gy.-- ArXiv pre-print available at: http://arxiv.org/abs/cond-mat/0509213Scaled particle theory for a binary mixture of hard discorectangles and for a binary mixture of hard rectangles is used to predict possible liquid-crystal demixing scenarios in two dimensions. Through a bifurcation analysis from the isotropic phase, it is shown that isotropic-nematic demixing is possible in two-dimensional liquid-crystal mixtures composed of hard convex bodies. This bifurcation analysis is tested against exact calculations of the phase diagrams in the framework of the restricted-orientation two-dimensional model (Zwanzig model). Phase diagrams of a binary mixture of hard discorectangles are calculated through the parametrization of the orientational distribution functions. The results show not only isotropic-nematic, but also nematic-nematic demixing ending in a critical point, as well as an isotropic-nematic-nematic triple point for a mixture of hard disks and hard discorectangles.One of the authors (Y.M.-R.) was supported by a Ramón y Cajal research contract from the Spanish MCyT. This work is part of the research Project Nos. BFM2003-0180, BFM2001-0224-C02-01, BFM2001-0224-C02-02, and BFM2001-1679-C03-02 (DGI) of the Ministerio de Ciencia y Tecnología (Spain).Publicad