Microswimmers Knead Nematics into Cholesterics.

Area of Science:

• Soft Matter Physics
• Active Matter Systems
• Liquid Crystal Science

Background:

• Active particles generate hydrodynamic stresses that can disrupt orientational order.
• Bend instabilities are observed in active nematics and quasi-two-dimensional living liquid crystals.

Purpose of the Study:

• To investigate the behavior of spherical microswimmers in a three-dimensional nematic liquid crystal.
• To understand the resulting hydrodynamic coupling and emergent phenomena.

Main Methods:

• Large-scale hydrodynamics simulations were employed.
• The system comprised spherical microswimmers within a three-dimensional nematic liquid crystal.

Main Results:

• Spontaneous chiral symmetry breaking was observed, leading to a continuously twisting nematic state.
• A helical director configuration, similar to cholesteric liquid crystals, emerged.
• This transition resulted from hydrodynamic coupling between liquid crystal elasticity and swimmer flow fields.
• A twist-bend instability of the nematic order was identified.
• The phenomenon was observed for both pusher and puller microswimmers.
• Particle trajectories were found to become helicoidal in the cholesteric state.

Conclusions:

• Hydrodynamic interactions between active particles and liquid crystals can induce novel ordered states.
• The study demonstrates a mechanism for spontaneous chiral symmetry breaking in active nematic systems.
• The findings link liquid crystal director dynamics with microswimmer motion.