Issue
EPL
Volume 85, Number 5, March 2009
Article Number 56003
Number of page(s) 6
Section Condensed Matter: Structural, Mechanical and Thermal Properties
DOI http://dx.doi.org/10.1209/0295-5075/85/56003
Published online 19 March 2009
EPL, 85 (2009) 56003
DOI: 10.1209/0295-5075/85/56003

Restricted orientation “liquid crystal” in two dimensions: Isotropic-nematic transition or liquid-gas one(?)

T. Fischer and R. L. C. Vink

Institute of Theoretical Physics, Georg-August-Universität Göttingen - Friedrich-Hund-Platz 1, 37077 Göttingen, Germany, EU


received 10 December 2008; accepted in final form 16 February 2009; published March 2009
published online 19 March 2009

Abstract
We present Monte Carlo simulation results of the two-dimensional Zwanzig fluid, which consists of hard line segments which may orient either horizontally or vertically. At a certain critical fugacity, we observe a phase transition with a two-dimensional Ising critical point. Above the transition point, the system is in an ordered state, with the majority of particles being either horizontally or vertically aligned. In contrast to previous work, we identify the transition as being of the liquid-gas type, as opposed to isotropic-to-nematic one. This interpretation naturally accounts for the observed Ising critical behavior. Furthermore, when the Zwanzig fluid is extended to more allowed particle orientations, we argue that in some cases the symmetry of a q-state Potts model with q > 2 arises. This observation is used to interpret a number of previous results.

PACS
64.70.F- - Liquid-vapor transitions.
47.11.Qr - Lattice gas.
64.70.M- - Transitions in liquid crystals.

© EPLA 2009