Fractionation in Gay-Berne liquid crystal mixtures

J. Antonio Moreno-Razo, Enrique Díaz-Herrera, and Sabine H. L. Klapp
Phys. Rev. E 76, 041703 – Published 9 October 2007

Abstract

We present a constant-pressure molecular dynamics simulation study of the phase behavior of binary (50:50) Gay-Berne liquid crystal mixtures consisting of elongated particles with different lengths (LA>LB) and equal diameters. We focus on systems at dense liquid-state conditions. Considering three mixtures characterized by different values of LA(B) and different length ratios q=LBLA<1, we find complex fluid-fluid phase behavior resulting from the interplay between nematic, smectic-A-type, or smectic-B-type orientational ordering, on the one hand, and demixing into two phases of different composition (fractionation), on the other hand. The driving “forces” of demixing transitions are the temperature and the length ratio. Indeed, in the system characterized by the largest value of q (q=0.86) orientational order occurs already in mixed states, whereas full fractionation is found at q=0.71. The two resulting states are either of type smectic-B-nematic (intermediate temperatures) or smectic-B-smectic-B (low temperatures). In the intermediate case q=0.80 we observe a stepwise ordering and demixing behavior on cooling the system from high temperatures. Moreover, our results show that the stability range of (partially) nematic structures in mixtures of sufficiently small q can be significantly larger than in the pure counterparts, in qualitative agreement with experimental observations.

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  • Received 23 April 2007

DOI:https://doi.org/10.1103/PhysRevE.76.041703

©2007 American Physical Society

Authors & Affiliations

J. Antonio Moreno-Razo and Enrique Díaz-Herrera

  • Departamento de Física, Universidad Autónoma Metropolitana-Iztapalapa, Mexico, D.F., Mexico

Sabine H. L. Klapp*

  • Stranski-Laboratorium für Physikalische und Theoretische Chemie, Sekretariat C7, Technische Universität Berlin, Strasse des 17, Juni 115, D-10623 Berlin, Germany and Institut für Theoretische Physik, Sekretariat PN 7-1, Technische Universität Berlin, Hardenbergstrasse 36, D-10623 Berlin, Germany

  • *sabine.klapp@fluids.tu-berlin.de

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Issue

Vol. 76, Iss. 4 — October 2007

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