Deformation of liquid drops and thin-films under the influence of an electric field Seminar

The ability to control the shape of droplets and thin films of liquid, via an externally applied electric field, has been exploited for technological applications including surface tension measurements, ink-jet printing, optical displays, and optimising the properties of polymer microlenses. Working with experimental collaborators at Nottingham Trent University we consider a system where a sessile droplet or film is placed on one substrate of a parallel plate capacitor. Experimentally we see that the liquid-air interface within the capacitor is distorted at low electric field strengths and, in some cases, an instability leads to the liquid bridging between the two capacitor plates.

Our work aims to describe the static and dynamic interface distortions as a function of key experimental parameters (droplet size, capacitor plate separation, electric field magnitude and contact angle). We derive straightforward analytical scaling relationships for static distortions, and a system of partial differential equations with the inclusion of fluid flow to describe the dynamics of distortions. Our approach avoids the requirement for detailed numerical methods in certain limiting cases, in particular for thin films or for droplets with contact angles of either almost 90 degrees or close to 0 degrees.

We investigate the limits of validity of these equations and compare with real experimental geometries with a range of liquids using fast imaging and optical interferometry.