The shape variations of the droplet with the applied potential bias were monitored using a Photron FASTCAM SA3 high speed camera controlled via Photron FASTCAM Viewer and a Storz Xenon Nova 300 light source. The recorded image captions under static conditions (i.e., after an equilibrium contact angle was achieved; within tenths to hundreds of ms) were analyzed using a custom-made Canny edge image processing algorithm in Matlab ® , Math-Works Inc., Natick MA, USA (for details see Papaderakis et al. ) to determine the equilibrium contact angle at each applied potential bias.