Dynamic Continuum Theory
The responses over time of a liquid crystal to external forces can be described by a dynamic continuum theory. The dynamic theory is founded on the classical fluid dynamics treatment of rotational and translational fluid flow. The liquid crystal, however, is special because its delicately ordered internal molecular orientation is significantly influenced by the internal translational motions within the liquid crystal, and the changing molecular orientations reciprocally affect the translational motions. In other words, any fluid-sliding motions will be coupled to the local dynamic orientational state of rotation, and the rotation in turn will affect the translation; the result is clearly observable effects on the polarization of light passing through, which is critical to the operation of liquid crystal displays.
In terms of hydromechanics, when an external force is applied, the liquid crystal molecules turn in a local but concerted manner, thereby producing a horizontal relative displacement of layers within the fluid, and the velocity gradient of the displacements produces a shear force that will in turn create a torque on the fluid, thereby generating further internal turning within the fluid.
Any mathematical theory describing the dynamic coupling of rotational and translational forces and motions of an anisotropic fluid at both the molecular and continuum fluid levels will of necessity be extremely complicated. The mathematical theory is further ...