Liquid behavior inside a reflective display pixel based on electrowetting

This article deals with the behavior of fluids inside a reflective display based on electrowetting. The advantage of using electrowetting as a principle for a reflective display has been demonstrated [R. A. Hayes and B. J. Feenstra, Nature (London) 425, 383 (2003)]. The principle is based on the controlled two-dimensional movement of an oil/water interface across a hydrophobic fluoropolymer insulator. The main objective of this article is to show experimentally the influence of the oil film curvature on the kinetics of the optical switch. For this we explore the electrowetting behavior and the fluidic motion as a function of several parameters, including addressing voltage, colored oil film thickness, oil type, and device size. The electro-optic characteristics and the switching dynamics of a single electrowetting pixel are studied. The results indicate that the competition between capillary forces and electrostatic forces governs the voltage driven oil contraction while capillary forces only drive the oil relaxation upon voltage removal. Consequently, a major parameter that controls the electrowetting behavior is the curvature of the oil/water interface. When increasing the oil film thickness or decreasing the device size, the oil film curvature increases. Hence, the capillary forces become stronger and the voltage required to achieve a particular oil contraction increases. With increasing curvature of the spherical oil cap, oil film relaxation, which is only capillary driven, is more rapid. The oil viscosity also plays a role in the speed of the oil movement. The reduction of the oil viscosity leads to an increase in the extent and speed of the oil/water interface movement. A linear relationship between the pixel capacitance and the resulting pixel white area percentage is found experimentally and is reconciled with an electrical model.

[2]  John A. Rogers,et al.  Dynamic tuning of optical waveguides with electrowetting pumps and recirculating fluid channels , 2002 .

[3]  Robert A. Hayes,et al.  Amorphous fluoropolymers as insulators for reversible low-voltage electrowetting , 2001 .

[4]  Mwj Menno Prins,et al.  Contact angles and wetting velocity measured electrically , 1999 .

[5]  S. Cho,et al.  Low voltage electrowetting-on-dielectric , 2002 .

[6]  B. Berge,et al.  Limiting phenomena for the spreading of water on polymer films by electrowetting , 1999 .

[7]  B. Berge,et al.  Variable focal lens controlled by an external voltage: An application of electrowetting , 2000 .

[8]  John Ralston,et al.  Electrowetting: a model for contact-angle saturation , 2000 .

[9]  Wolfgang Göpel,et al.  Competitive Electrowetting of Polymer Surfaces by Water and Decane , 2000 .

[10]  R. Fair,et al.  Electrowetting-based actuation of liquid droplets for microfluidic applications , 2000 .

[11]  John Ralston,et al.  Electrically Induced Changes in Dynamic Wettability , 2000 .

[12]  L. G. J. Fokkink,et al.  Fast Electrically Switchable Capillary Effects , 1998 .

[13]  B. Berge,et al.  Electrowetting : a recent outbreak , 2001 .

[14]  Y. Shikhmurzaev A two-layer model of an interface between immiscible fluids , 1993 .

[15]  Bruno Berge,et al.  Investigation of effective interface potentials by electrowetting , 2002 .

[16]  T. Blake,et al.  An Investigation of Electrostatic Assist in Dynamic Wetting , 2000 .

[17]  J. Jacobson,et al.  An electrophoretic ink for all-printed reflective electronic displays , 1998, Nature.

[18]  M. Vignes-Adler,et al.  Wetting transition of n-alkanes on concentrated aqueous salt solutions. Line tension effect , 1997 .

[19]  A. Goebel,et al.  Interfacial Tension of the Water/n-Alkane Interface , 1997 .

[20]  H. Verheijen,et al.  REVERSIBLE ELECTROWETTING AND TRAPPING OF CHARGE : MODEL AND EXPERIMENTS , 1999, cond-mat/9908328.

[21]  J. Coninck,et al.  Dynamics of Spontaneous Spreading under Electrowetting Conditions , 2000 .

[22]  B. J. Feenstra,et al.  Video-speed electronic paper based on electrowetting , 2003, Nature.

[23]  Mwj Menno Prins,et al.  Fluid control in multichannel structures by electrocapillary pressure. , 2001, Science.