Molecular-statistical approach to the description of tilted smectic phases

ABSTRACT

We have investigated the origin of spontaneous polar ordering in smectic liquid crystals in the framework of molecular-statistical approach. The polar order parameter is introduced as $p=P/\left(\rho \mu \right)$, where P is the polarization, μ is the molecular transverse electric dipole and ρ is the concentration of molecules. We have shown that piezoelectric spontaneous polarization should generally be related to the bent shape of molecules (even for the molecules which are not normally considered as bent-shaped), while both chirality and polarization appear due to the presence of the electric dipole in the direction perpendicular to the plane of molecular bend. The molecular origin of the flexoelectric effect in tilted smectic phases and the influence of the dipole–dipole interaction on the polar order parameter is also studied. The principal result of the paper is elaboration of a self-consistent mean theory for the description of polarization in Sm-$C^{\ast }$ and Sm-$C_A^{\ast }$ phases.

KEYWORDS:

• Liquid crystals
• molecular theory
• spontaneous polarization
• flexoelectric effect

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was partially supported by Russian Science Foundation (RSF), research project no. 16-43-03010.