Multiphysics simulation of fluid interface shapes in microfluidic systems driven by electrowetting on dielectrics

We present a highly efficient simulation method for the calculation of three-dimensional quasi-static interface shapes under the influence of electric fields. The method is especially useful for the simulation of microfluidic systems driven by electrowetting on dielectrics because it accounts automatically and inherently for the highly non-trivial interface shape in the vicinity of the triple-phase contact. In particular, the voltage independence of the local contact angle predicted based on analytical considerations is correctly reproduced in all our simulations. For the calculation of the shape of the interface, the geometry is triangulated and the mesh nodes are shifted until the system energy becomes minimal. The same mesh is also used to calculate the electric field using the boundary-element method. Therefore, only the surface of the geometry needs to be meshed, and no volume meshes are involved. The method can be used for the simulation of closed systems with a constant volume (e.g., droplet-based microfluidics) while preserving the volume very precisely as well as open systems (e.g., the liquid–air interface within micro-cavities or capillaries). Additional effects, such as the influence of gravitational forces, can easily be taken into account. In contrast to other efficient simulations, such as the volume-of-fluid, level-set, or phase-field methods, ideally, sharp interfaces are obtained. We calculate interface shapes for exemplary systems and compare with analytical as well as experimental results.