Role of confinement in stabilizing 3D Active nematic droplets*

Kinesin motors and microtubules are the biological building blocks that convert chemical energy into mechanical work. When suspended in water, they assemble in a 3D active isotropic liquid crystal. When suspended in a passive colloidal liquid crystal made of elongated fd viruses, they assemble in a 3D active nematic liquid crystal.
The strategy of building composite materials where only a fraction of the rods are active allow to decouple nematic elasticity and activity, which is challenging in a single component active material. Here, nematic elasticity is controlled by the density of the passive nematic background, while the activity is controlled by the kinesin/MT concentrations. We confined the 3D active nematic in droplets using an oil-water emulsion. Preliminary results show that confinement can stabilize the inherent chaotic dynamics of 3D active nematic droplets. We study how the critical radius depends on the activity and nematic elasticity. The existence of such transition between a quiescent state and a flowing state is reminiscent of the effect of confinement in the Fréedericksz transition for passive liquid crystals under an external magnetic field.