Lattice Boltzmann study of chemically-driven self-propelled droplets

Area of Science:

• Fluid Dynamics
• Soft Matter Physics
• Computational Physics

Background:

• Self-propelled liquid droplets exhibit complex behaviors driven by surface tension gradients.
• Marangoni-like flow, induced by surfactant concentration variations, is a key mechanism for droplet motion.
• Understanding droplet interactions is crucial for applications in microfluidics and materials science.

Purpose of the Study:

• To numerically investigate the self-propulsion of isolated and interacting liquid droplets.
• To analyze the role of surfactant concentration and distribution on droplet dynamics.
• To explore the hydrodynamic interactions between two self-propelled droplets at varying distances.

Main Methods:

• A numerical model incorporating Navier-Stokes and convection-diffusion equations was employed.
• The lattice Boltzmann method was coupled with finite-difference schemes for simulations.
• Both isolated droplet motion and pairwise interactions were simulated.

Main Results:

• Surfactant migration to the interface generated a quadrupolar vortex, driving droplet motion.
• Dilute bulk surfactants resulted in a weaker dipolar flow field.
• Droplet interactions showed distance-dependent behaviors: attraction, steady states, scattering, and passive droplet advection.

Conclusions:

• The study elucidates the mechanisms of self-propulsion and interaction in liquid droplets.
• Hydrodynamic interactions significantly influence droplet dynamics, especially at close proximity.
• The findings provide insights into the control and prediction of active droplet systems.