Driving Liquid Barrels with Electrowetting

Liquid barrels---droplets trapped in a wedge geometry---appear in biological physics, granular media and microfluidics. Recent electrowetting experiments show that the equilibrium configuration of a liquid barrel is a truncated sphere that intersects the wedge walls with an equilibrium contact angle adjusted by the applied voltage (D. Baratian, Soft Matter, 2015). The ability to control the motion of liquid barrels promises applications of droplet manipulation in microfluidic channels; however, the dynamics to new equilibria induced by sudden changes in voltage has not been studied in detail. In this talk, we present experiments and simulations of the dynamics of liquid barrels driven by electric fields.

To model the liquid-barrel dynamics, we carried out lattice-Boltzmann simulations of the coupled Navier-Stokes and Cahn-Hilliard equations (T. Krüger, Springer, 2016). To account for electrowetting, we equipped our lattice-Boltzmann algorithm with a solver of the electric potential field; this allows us to analyse in detail the competition of viscous, capillary and electrostatic forces that act on the shape of the liquid-barrel.