Liquid crystal electrokinetics

- By: Jorge Viñals
- Affiliation: U. of Minnesota
- Date: 2018-03-07T14:30:00+00:00
Electrokinetic phenomena in a nematic fluid are considered, involving
either fluid flow under designed director patterns, or particle motion
when one or more dielectric particles are suspended in the nematic
matrix. The long range orientational order of the nematic constitutes a
fluid with anisotropic properties that enables charge separation in the
bulk under an applied electric field, and leads to streaming flows even
when the applied field is oscillatory. We present a quantitative
transport model of the mechanisms inducing spatial charge separation in
the nematic, and of the structure and magnitude of the resulting flows.
The fundamental solutions for charge distribution and flow velocities
induced by designed periodic director patterns, and by isolated
disclinations are given. The same model is used to study the motion of a
single particle-hyperbolic hedgehog pair. We find this motion to be
parallel to the defect-particle center axis, independent of field
orientation. For a two particle configuration, we find that the relative
force of
electrokinetic origin is attractive in the case of particles with
perpendicular director anchoring, and repulsive for particles with
tangential director anchoring. The study reveals large scale flow
properties that are respectively derived from the topology of the
configuration alone and from short scale hydrodynamics phenomena in the
vicinity of the particle and defect.