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Dynamics of colloids and solitons in liquid crystals - Oleg D. Lavrentovich

Liquid Crystal Institute and Department of Physics, Kent State University, Kent, Ohio, USA

Behavior of small particles in fluids has fascinated scientists for centuries. Phenomena such as Brownian motion, sedimentation, electrophoresis continue to inspire research and innovation. The fluid in which the colloids move is typically isotropic, such as water. There is a growing interest to the dynamics of particles in crowded microenvironments with some elements of order.

We explore behavior of colloids in the simplest ordered fluid, a nematic liquid crystal, in which elongated molecules are aligned along a preferred direction called the director. Orientational order leads to long-range elastic interactions that support levitation of colloids and cause anomalous Brownian diffusion. Equally strong changes are seen in dynamics powered by the electric field.

The liquid crystalline medium enables new mechanisms of electrophoresis and electro-osmosis in which the characteristic velocities grow with the square of the applied field (rather than linearly as in classic electrokinetics). The effect can be used to propel particles that are not charged, to separate colloids that differ only by their surface properties, to create steady flows with vortices powered by an AC field. The mechanism is rooted in charge separation at spatial distortions of the director and in intrinsic anisotropy of the liquid crystal. Most recent studies demonstrate that the nematics acted upon by an AC electric field produce propagating 3D particle-like solitary waves of director distortions. The main results are published in :

  1. Nature 467, 947-950 (2010),
  2. Science 342, 1351-1354 (2013),
  3. Nature Comm. 5, 5033 (2014) and 9, 2912 (2018),
  4. Liquid Crystals (2018).

Current work is supported by NSF DMREF grant DMS-1729509.


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