Density functional theory of freezing of a system of conjugated oligomers parameterised via Gay–Berne potential

ABSTRACT

Density functional theory (DFT) of freezing is used to study the isotropic–nematic, isotropic–smectic A and nematic–smectic A phase transitions in a system of large, semi-flexible conjugated oligomers parameterised within Gay–Berne (GB) potential. The pair correlation functions of the isotropic fluid, used as structural inputs in the DFT, are calculated by solving the Percus–Yevick integral equation theory. Large number of spherical harmonic coefficients of each orientation-dependent functions has been considered to ensure the numerical accuracy at different densities and temperatures for the system of these model GB ellipsoids having large aspect ratio (length-to-breadth ratio). We found that the system of GB ellipsoids parameterised for conjugated oligomers shows stable isotropic, nematic and smectic A phases. At low temperatures, on increasing the density, isotropic fluid makes a direct transition to smectic A phase. Nematic phase get stabilised in between the isotropic and smectic A phases on increasing the temperature. Using the transition parameter obtained through the DFT, we have plotted the temperature–density and pressure–temperature phase diagrams which are found to be qualitatively similar to the one obtained in simulations for the systems with low aspect ratio GB particles.

Graphical Abstract

KEYWORDS:

• Phase transition in liquid crystals
• models and theories of liquid crystal structure
• density functional theory

Acknowledgement

The authors thank Prof. Y. Singh for many insightful discussions.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

P Mishra wishes to acknowledge the financial support of SERB, Department of Science and Technology, New Delhi through a project grant [D. O. no. SR/S2/CMP-0140/2012]. J Ram would like to thank UGC New Delhi for granting emeritus fellowship.