Hypothesis

Colloidal particles in a nematic liquid crystal (NLC) exhibit very different behaviour than that observed in an isotropic medium. Such differences arise principally due to the nematic-induced elastic stresses exerted as due to the interaction of NLC molecules with interfaces, which competes with traditional fluid viscous stresses on the particle.

Theory

A systematic mathematical analysis of the behaviour of particles placed in the flow within an NLC microfluidic channel is performed using the continuum Beris-Edwards framework coupled to the Navier-Stokes equations. We impose strong homeotropic anchoring on the channel walls and weak homeotropic anchoring on the particle surfaces.

Findings

The viscous and NLC forces act on an individual particle in opposing directions, resulting in a critical location in the channel where the particle experiences zero net force in the direction perpendicular to the flow. For multi-particle aggregation we show that the final arrangement is independent of the initial configuration, but the path towards achieving equilibrium is very different. The results of our work uncover new mechanisms for particle separation and routes towards self-assembly.