8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

Fri 911:10-14:00P3.39Generalised van der Waals-Onsager approach forattractive oblate cylinder particlesLiang Wu, 1 Erich Muller, 1 and George Jackson 11 Imperial College London, Department of Chemical Engineerings, Roderic hill BuildingACEX610 SW7 2AZ, London, United KingdomA perturbation theory [1, 2] is employed to construct the free energy functional capable ofdescribing the isotropic and nematic phases of attractive oblate cylinder particles. The modelmesogen is a hard-core (purely repulsive) cylindrical disc decorated with an attractive potential(e. g. , of square-well, Lennard-Jones, or Yukawa for) acting at the centre of mass of the harddisc. The resulting overall potential is anisotropic due to the exclusion of the hard core. Weuse the Onsager trial function [3, 4] to characterize the orientational order in the nematic phase,thus expressing the free energy functional in an algebraic form using a scaled Onsager hard-corereference. From this, a closed equation of state for attractive oblate cylinder particles is obtainedwith a high-temperature perturbation expansion. The phase diagram of oblate cylinder particlesis reported. As compared to the phase diagram of the athermal analogue, [5], the addition of anattractive potential gives rise to a more extensive region of isotropic (liquid)-nematic with a higherdegree of orientational order coexistence. We predict that the system of attractive oblate cylindersof aspect ratio ∼ 10 exhibits vapor-liquid-nematic phase equilibria. By considering thinner oblatecylinder of aspect ratio ∼ 20, the isotropic-nematic transition is shifted to lower density regions,and the vapor-liquid equilibrium becomes metastable with respect to a region of isotropic-nematiccoexistence. The effect of the anisotropy of attractive potential on the phase diagram is alsoexamined.[1] M. Franco-Melgar, A. J. Haslam, G. Jackson, Mole. Phys. 107, 2329 (2009).[2] H. H. Wensink, G. Jackson, J. Chem. Phys. 130, 234911 (2009).[3] L. Onsager, Ann. N. Y. Acad. Sci. 51, 627 (1949).[4] M. Franco-Melgar, A. J. Haslam, G. Jackson, Mole. Phys. 106, 649 (2008).[5] H. H. Wensink, H. N. W. Lekkerkerker, Mole. Phys. 107, 2111 (2009).39