Dynamics of Colloids in Liquid Crystals
Behavior of small particles in fluids has fascinated scientist for centuries. Phenomena such as Brownian motion, sedimentation, and electrophoresis continue to inspire cutting-edge research and innovation. The fluid in which the colloidal particles move is typically isotropic, such as water or a dilute polymer solution. There is a growing interest to the dynamics of colloids in crowded environments with some elements of order. As a model system, we explore colloidal dynamics in a nematic liquid crystal. Orientational order of the liquid crystal leads to long-range elastic interactions that dramatically alter static behavior of the colloids (1) and support their levitation (2). Equally strong changes are seen in the dynamics. The liquid crystalline environment enables anomalous Brownian diffusion (3) and new mechanisms of electrokinetics with nonlinear (quadratic) dependence of flow velocities on the applied electric field (4). Addition of swimming bacteria to a non-toxic liquid crystal creates an experimentally controlled active system, which exhibits a cascade of transitions from equilibrium to non-equilibrium orientational patterns triggered by an increase of activity (5). Patterned director fields (6) including those with topological defects (7) control the threshold and polarity of active flows and spatial distribution of microswimmers (8). The new phenomena are rooted in anisotropy of the liquid crystals properties, such as surface tension, viscosity and elasticity, dielectric permittivity and conductivity (2).
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