A physical model describing the electro-optic behavior of switchable optical elements based on electrowetting

TLDR

Reflective display pixels have been demonstrated using voltage‑controlled two‑dimensional movement of an oil/water interface across a hydrophobic fluoropolymer insulator. The study reports a physical model describing the basic electro‑optic behavior of electrowetting‑based optical elements. The model extends classical electrowetting theory to confined oil/water interfaces, accounting for the oil layer’s spatial extent (<5 mm) approximated as a spherical cap. Calculated results agree closely with experiment without fitting parameters, and the model enables prediction and optimization of device electro‑optics across parameters such as oil film thickness, insulator thickness, element size, and interfacial tension.

Abstract

Recently, we have demonstrated reflective display pixels based on the voltage-controlled two-dimensional movement of an oil/water interface across a hydrophobic fluoropolymer insulator [R. A. Hayes and B. J. Feenstra, Nature (London) 425, 383 (2003)]. Here a physical model is reported that describes the basic electro-optic behavior of these electrowetting-based optical elements. The model extends the classical electrowetting theory developed for a free water droplet on an insulator surface to the controlled two-dimensional movement of a confined oil/water interface. The model takes into account the spatial extent of the oil layer (&amp;lt;5mm), where the oil film is well approximated by a spherical cap. The calculated results are in very good agreement with experimental data without employing fitting parameters. The model can be used to predict and optimize the electro-optic behavior of devices as a function of a range of well-defined parameters including the oil film thickness, the thickness of the insulating layer, the size of the optical element, and the oil/water interfacial tension.