Seminar über aktuelle Fragen zur Dynamik komplexer Fluide: Electrostatic manipulation of liquid droplets
10:15 - 11:15
Prof. Carl Brown
Nottingham Trent University, UK
Max-Planck-Institut für Dynamik und Selbstorganisation (MPIDS)
Two related topics of droplet dynamics will be presented
(1) Electric field induced deformation of sessile droplets: An axisymmetric sessile droplet supported on the inside face of a parallel plate capacitor is distorted away from its equilibrium spherical cap profile when the electric field is applied, with the apex of the droplet moving towards the opposing capacitor plate. Previous theoretical work on this geometry has tended to use numerical methods, including finite element analysis, to solve the coupled electrostatic and stress (surface, gravitational and electric) balance equations along with the interfacial boundary conditions. We have performed an experimental and theoretical analysis of the distortion of spherical cap shapes for conducting or dielectric droplets, including the dynamic response to the abrupt application or removal of the electric field, in limiting cases of small contact angles or of a close to hemispherical droplet shape.
(2) Dewetting from a liquid film into a single droplet : Our recent work on interface-localized liquid dielectrophoresis has led to the ability to induce and control equilibrium liquid film shapes using a voltage, also called dielectrowetting. Here we show that interface-localized liquid dielectrophoresis can also be used to create an initial static circular shaped liquid film on a non-wetting surface. On-demand quenching of the non-uniform electric field permits quantitative study of subsequent dewetting into a single macroscopic droplet, which is normally difficult to study. We observe two distinct regimes in the dynamic dewetting, firstly retreat of a liquid rim at a constant contact angle and contact line speed, followed at longer times by a second regime corresponding to the formation of a spherical cap droplet with an exponential approach to equilibrium. This process sharply contrasts with the process of wetting from a small macroscopic droplet into a liquid film, which proceeds by a sequence of spherical cap droplet shapes.