Phase behavior of disklike hard-core mesogens

Abstract

We report a computer-simulation study of a system of "hard cut spheres, " oblate particles that are obtained by slicing off' the top and bottom caps of a sphere at a distance L/2 from the equatorial plane. This system serves as a model for a disklike mesogen. The phase behavior of this system is found to be strongly dependent on the length-to-width ratio (L /D) of the particles. In addition to isotropic and solid phases, we find nematic and columnar phases for L /D =0.1. For L/D =0.2 we find a columnar phase, and a phase with cubic orientational order but no translational order. For L /D =0. 3, only the isotropic Quid and the solid are stable. Where possible, we have located the phase transitions.

Evidence of the hexagonal columnar liquid-crystal phase of hard colloidal platelets by high-resolution SAXS

“…Model systems of colloidal platelets that do show the I-N transition have recently become available [34,35], confirming both Onsager's theory and computer simulations [36]. From computer simulations by Veerman and Frenkel [37], and later Zhang et al [38], it was found that hard platelets may also form another liquid-crystal phase, namely the orientationally and 2D translationally ordered columnar (C) phase. This phase has also been observed experimentally in suspensions of sterically stabilised and charged colloidal plates [39][40][41].…”

Isotropic−Nematic Density Inversion in a Binary Mixture of Thin and Thick Hard Platelets

“…13 In fact, the Onsager theory also overvalues the coexisting number densities as compared to the simulations. It turns out that Parsons' approach both narrows the miscibility gap and shifts the coexisting densities …”

“…The relative importance of three-body interactions in terms of the ratio B 3 /B 2 2 (with B 3 the third virial coefficient) has been estimated by Onsager 1 at O(1). More accurate predictions were obtained from computer simulations, 13 giving B 3 /B 2 2 ≈ 0.51 for disks with aspect ratio L/D ) 0.1. These results clearly indicate that Onsager's approach of truncating the free energy after the second virial coefficient cannot be justified (quantitatively) for systems of platelets.…”

“…An important consequence is that, in our approximation, the orientation of the platelets in the nematic phase is solely determined by the diameter of the platelets, which is identical for both components. It is important to realize that the thickness does not enter into the free energy anywhere else than via the O(L/D) term in (13). So, we can simplify our calculations considerably by using a single variational parameter, R ) R j ) R k , which holds for both components.…”

Numerical Techniques to Study Complex Liquids

“…liquid crystals). For details, the reader is referred to refs [36,37,38,39,40,41]. Finally, thermodynamic integration techniques are particularly useful to compute the Gibbs free energy of mixtures.…”