Dr. Sebastian Dehe
Electroosmotic flow over superhydrophobic surfaces; Electrohydrodynamic instabilities at liquid-liquid interfaces
work +49 6151 16-24280
fax +49 6151 16-24278
Electrohydrodynamic instabilities at liquid-liquid interfaces
Liquid-liquid interfaces deform under the actuation by electric fields, and disintegrate at sufficiently high field strengths. The most prominent example is the so-called Taylor cone, where an interface takes a conical shape and ejects a fine jet or small droplets from the tip of the cone. In addition, other electrically triggered instabilities exist, such as the electric analogue of the Faraday instability.
In this project, the response of a liquid-liquid interface is studied versus spatially inhomogeneous DC-fields, as well as spatially homogeneous AC fields. For the spatially inhomogeneous DC-field, the existence of an alternative deformation mode, coexisting with the classical Taylor-cone mode is shown and attributed to the viscous interaction of the emitted charged droplets with the background fluid. For the spatially homogeneous AC fields, the critical field strength as well as the resulting wave-length of the electrically driven Faraday-instability is studied.
In this project, high-speed imaging of the interfacial instabilities is used in conjunction with image processing and electrical current measurements on the nA-scale to characterize the instabilities. The experimental observations are reproduced by numerical simulations in Comsol Multiphysics to verify the driving mechanism. The wavelengths of the Faraday-instability are measured using a refraction-based technique, which allows the reconstruction of the interface.