Poisson-Bracket Approach to the Dynamics of Nematic Liquid Crystals. The Role of Spin Angular Momentum

TL;DR

This paper develops a Poisson-bracket formalism to derive the dynamics of nematic liquid crystals, explicitly including spin angular momentum, and clarifies conditions under which classical equations are recovered.

Contribution

It introduces a formalism that incorporates spin angular momentum as an independent field in nematic liquid crystal dynamics, extending traditional models.

Findings

Equations reduce to Leslie-Ericksen form under specific conditions.

Derived equations include inertial effects of director rotation.

Dissipative coefficients depend on spin angular momentum parameters.

Abstract

Nematic liquid crystals are well modeled as a fluid of rigid rods. Starting from this model, we use a Poisson-bracket formalism to derive the equations governing the dynamics of nematic liquid crystals. We treat the spin angular momentum density arising from the rotation of constituent molecules about their centers of mass as an independent field and derive equations for it, the mass density, the momentum density, and the nematic director. Our equations reduce to the original Leslie-Ericksen equations, including the inertial director term that is neglected in the hydrodynamic limit, only when the moment of inertia for angular momentum parallel to the director vanishes and when a dissipative coefficient favoring locking of the angular frequencies of director rotation and spin angular momentum diverges. Our equations reduce to the equations of nematohydrodynamics in the hydrodynamic limit but with dissipative coefficients that depend on the coefficient that must diverge to produce the Leslie-Ericksen equations.