Computer simulation of charged hard spherocylinders at low temperatures

Abstract

In this work we report the stability of liquid crystalline phases of charged hard spherocylinders (CHSC) of aspect ratio L/σ=5 at low temperatures using NPT Monte Carlo computer simulations. Following the methodology used in previous work [C. Avendaño, A. Gil-Villegas, E. González-Tovar, J. Chem. Phys. 128, 044506 (2008); Chem. Phys. Lett. 470, 67 (2009)], long-range coulombic interactions are handled using the Wolf method. The supramolecular organization of CHSC is obtained by compression of a low-density isotropic state. The system under consideration exhibits the expected isotropic, nematic, smectic-A, and crystal phases. However two important phenomena emerge at low temperatures, namely the existence of an isotropic–nematic–smectic triple point, with the ending of the nematic phase for lower temperatures, and the apparent hexatic arrangement of the layers in the smectic phases. Assuming that the smectic-layers behave as quasi-bidimensional systems, lowering the temperatures is possible to observe the formation of hexatic phases, which are detected analysing the structure factor, order parameters and distribution functions. This hexatic ordering indicates that the CHSC phase diagram presents a smectic-B phase at low temperatures.

Keywords:

• liquid crystals
• computer simulation
• Monte Carlo method

Acknowledgements

Financial support for this work was given by PROMEP (México), and Consejo Nacional de Ciencia y Tecnología (CONACYT, México), through a PhD scholarship (G.J.S.) and grants 61418, 58470. C.A. also acknowledges the United Kingdom Engineering and Physical Sciences Research Council (EPSRC) Grant No. EP/E016340, ‘Molecular System Engineering’.