Active nematics on flat surfaces: from droplet motility and scission to active wetting

TL;DR

This paper explores the complex behaviors of active nematic droplets on flat surfaces, revealing how activity influences droplet motion, scission, wetting, and evaporation, and providing a unified theoretical framework for these phenomena.

Contribution

It offers a comprehensive continuum hydrodynamic model that describes various dynamical regimes of active nematic droplets, highlighting the role of activity, size, and surface properties.

Findings

Active activity controls droplet self-propulsion and scission.

Droplet evaporation is driven by active nematics concentration.

Dynamical regimes depend on active capillary number and surface parameters.

Abstract

We consider the dynamics of active nematics droplets on flat surfaces, based on the continuum hydrodynamic theory. We investigate a wide range of dynamical regimes as a function of the activity and droplet size on surfaces characterized by strong anchoring and a range of equilibrium contact angles. The activity was found to control a variety of dynamical regimes, including the self-propulsion of droplets on surfaces, scission, active wetting and droplet evaporation. Furthermore, we found that on a given surface (characterized by the anchoring and the equilibrium contact angle) the dynamical regimes may be controlled by the active capillary number of suspended droplets. We also found that the active nematics concentration of the droplets varies with the activity, affecting the wetting behaviour weakly but ultimately driving droplet evaporation. Our analysis provides a global description of a wide range of dynamical regimes reported for active nematics droplets and suggests a unified description of droplets on surfaces. We discuss the key role of the finite size of the droplet and comment on the suppression of these regimes in the infinite size limit, where the active nematics is turbulent at any degree of activity.