Pressure-induced phase transitions in liquid crystals: A molecular field approach

A rigorous microscopic treatment of a nematic fluid system based on a pairwise interaction potential is immensely complex. For studying such systems molecular field theories are often the standard method of choice. In this paper we have chosen a simple effective potential $U=\frac{u_4}{v^4}-\frac{u_2}{v^2}-\frac{A{u}_2}{v^2}〈P_2〉P_2(cos\vartheta )$ to study an isothermal-isobaric ensemble describing a liquid crystalline system. Using this we have studied in particular the pressure dependence of liquid crystalline phase transitions.

Figure 1

Phase diagram showing the nematic, isotropic liquid, and gaseous phases.

Figure 2

Variation of orientational order parameter with temperature.

Figure 3

Variation of orientational order parameter with pressure.

Figure 4

Orientational order parameter vs $T$ plot at different constant values of volume.

Figure 5

Comparison of orientational order parameter values at constant volume and constant pressure.

Figure 6

Variation of volume with pressure for different constant values of temperature showing the isotropic liquid-gas phase transition.

Figure 7

Variation of volume with pressure for different constant values of temperature showing the first-order nematic-isotropic liquid phase transition.

Figure 8

Variation of isothermal compressibility with temperature showing the nematic-isotropic phase transition.

Figure 9

Variation of volume expansivity with temperature showing the nematic-isotropic phase transition.

Figure 10

Variation of isothermal compressibility with temperature showing the isotropic liquid-vapor phase transition.

Figure 11

Variation of volume expansivity with temperature showing the isotropic liquid-vapor phase transition.