Abstract
Abstract
Microscopic active droplets are of interest since they can be used to transport matter from one point to another. The challenge is to control the trajectory. In this work, we demonstrate an approach to control the direction of active droplet propulsion by a photoresponsive cholesteric liquid crystal environment. The active droplet represents a water dispersion of bacterial B. subtilis microswimmers. When placed in a cholesteric, a surfactant-stabilized active droplet distorts the local director field, producing a point defect-hedgehog, which breaks the fore-aft symmetry. The chaotic motion of the bacteria inside the droplet is rectified into directional motion by the asymmetric director field outside the droplet. When the pitch of the cholesteric is altered by visible light irradiation, the asymmetry axis and thus the droplet trajectory realign along a new direction. Droplets realign counterclockwise on exposure to light of 535 nm, and clockwise on exposure to light of 450 nm, as dictated by the photoinduced change in the handedness of the cholesteric. The strategy allows for a non-contact dynamic control of active droplets trajectories and demonstrates the advantage of orientationally ordered media in control of active matter over their isotropic counterparts.
Publisher
Research Square Platform LLC
Reference35 articles.
1. Ramaswamy, S. Active matter. Journal of Statistical Mechanics: Theory and Experiment 2017, 054002 (2017).
2. We the droplets: A constitutional approach to active and self-propelled emulsions;Birrer S;Curr Opin Colloid Interface Sci,2022
3. Carenza, L. N., Gonnella, G. & Negro, G. Motility and self propulsion of active droplets. in Out-of-Equilibrium Soft Matter: Active Fluids (eds. Gentile, L., Kurzthaler, C. & Stone, H. A.) 1–41 (2022).
4. Self-Propulsion of Chemically Active Droplets;Michelin S;Annu Rev Fluid Mech,2023
5. Solute induced jittery motion of self-propelled droplets;Dwivedi P;Physics of Fluids,2021