Statistical Properties of Autonomous Flows in 2D Active Nematics

TL;DR

This study investigates the statistical properties of chaotic flows in 2D active nematic liquid crystals powered by kinesin motors, revealing exponential vortex area distributions and a link between ATP concentration and active stress.

Contribution

It provides experimental validation of hydrodynamic theories and connects ATP-driven motor activity to macroscopic flow properties in active nematics.

Findings

Vortex areas are exponentially distributed.

Characteristic length scale depends on ATP concentration.

Possible mapping between ATP levels and active stress.

Abstract

We study the dynamics of a tunable 2D active nematic liquid crystal composed of microtubules and kinesin motors confined to an oil-water interface. Kinesin motors continuously inject mechanical energy into the system through ATP hydrolysis, powering the relative microscopic sliding of adjacent microtubules, which in turn generates macroscale autonomous flows and chaotic dynamics. We use particle image velocimetry to quantify two-dimensional flows of active nematics and extract their statistical properties. In agreement with the hydrodynamic theory, we find that the vortex areas comprising the chaotic flows are exponentially distributed, which allows us to extract the characteristic system length scale. We probe the dependence of this length scale on the ATP concentration, which is the experimental knob that tunes the magnitude of the active stress. Our data suggest a possible mapping between the ATP concentration and the active stress that is based on the Michaelis-Menten kinetics that governs motion of individual kinesin motors.