Sophisticated oil film geometries through incomplete electrical dewetting by feedback control and Fourier construction

Abstract

Existing techniques for electronic control of the interface between two immiscible fluids are typically limited to simple periodic geometries (symmetric waves) or spherical geometries (only two principle radii of curvature). Presented here, is a new technique with much more sophisticated electronic control of fluid meniscus geometry. Previously undemonstrated two-fluid interfaces, such as asymmetric saw-tooth profiles, are created by dynamic modulation of an incomplete dewetting state for an oil film covering an array of control electrodes, with the oil film itself covered by an electrically conductive fluid acting as the ground electrode. Two distinct approaches are demonstrated: (1) application of voltages, electrical capacitance sensing of meniscus geometry, followed by further feedback control of the applied voltages based on the sensed electrical capacitance; (2) use of multiple periodic voltage waveforms and wave propagation across the meniscus to build up complex meniscus geometries by Fourier construction. These approaches are demonstrated in this work by a proven electro-hydrodynamic modeling method, which couples the Maxwell stress tensor with the laminar phase field of the oil–water dual phase. This work could serve numerous applications including particle or fluid transport (e.g. lab-on-chip), or adaptive optical surfaces (e.g. liquid prism arrays). Importantly, the results can be achieved using conventional materials, and the fluids respond with speeds that are adequately slow (ms–μs) such that even conventional control electronics (μs–ns) are more than adequate. Furthermore, because the conducting fluid never dewets the oil film from the solid surface, dielectric degradation issues are likely eliminated.