Berlin 2018 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 18: Focus: Droplets (joint session DY/CPP)

CPP 18.9: Vortrag

Montag, 12. März 2018, 17:45–18:00, BH-N 334

Contact angle saturation in electrowetting of nanodrops — •Nicolas Rivas and Jens Harting — Forschungszentrum Jülich GmbH, Helmholtz Institute Erlangen-Nürnberg for Renewable Energy (IEK-11)

The wetting angle of a drop in contact with a substrate can be modified by applying an external electric field, a phenomenon referred to as electrowetting. The degree of wetting most commonly increases with the applied electric field, although in many cases only until a certain angle, after which the electric field has little or no influence on the wetting properties of the drop. This limit behavior is referred to as contact angle saturation (CAS). The origin of CAS is unknown, with numerous possible explanations present in the literature. In the following work we investigate electrowetting and CAS at the nanoscale. A model is proposed that takes into account the hydrodynamics of two fluids and the diffusion of charged solutes (ions). The numerical methodology used to solve this model is presented together with validation cases. The model is used to study electrowetting of conductive sessile drops as a function of the overall ion concentration and the relative conductivity of the two fluid phases. The variations of the contact angle are consistent with previous studies. We also observe CAS in regions of low salt concentration. A mechanism for CAS is proposed based on the progressive loss of ions from the drop as the electric field increases. This is discussed in relation to previously proposed mechanisms for CAS, which in general involve physics which our model does not intend to capture.