Electrowetting: Electrocapillarity, saturation, and dynamics

AbstractElectrowetting is an electrocapillary phenomenon, i.e. the surface charge generated at the solid-liquid interface through an external voltage improves the wettability in the system. The Young-Lippmann equation provides the simplest thermodynamic framework and describes electrowetting adequately. Saturation, i.e. the reduced or nullified effectiveness of the external voltage below a threshold contact angle value, was and remains the most controversial issue in the physics of electrowetting. A simple estimation of the limits of validity of the Young model is obtained by setting the solid-liquid interfacial tension to zero. This approach predicts acceptably the change in electrowetting mechanism but not the minimal value of the contact angle achievable during electrowetting. The mechanism of saturation is, in all probability, related to charge injection into the dielectric layer insulating the working electrode but physical details are scarce. Surface force and spectroscopic techniques should be deployed in order to improve our understanding of the surface charging of insulators immersed in conductive liquids. Electrowetting in solid-liquid-liquid systems is generally more effective and robust. Electrowetting offers new ways of studying the dynamics of liquid movement as it allows selective changes in the wettability of the system.

[1]  Frieder Mugele,et al.  Electrowetting-induced oil film entrapment and instability. , 2006, Physical review letters.

[2]  P. Gennes.  Wetting: statics and dynamics , 1985 .

[3]  Jean Cross,et al.  Electrostatics, Principles, Problems and Applications , 1987 .

[4]  Norio Sato,et al.  Electrochemistry at Metal and Semiconductor Electrodes , 1998 .

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

[6]  Behrouz Abedian,et al.  Low voltage electrowetting using thin fluoroploymer films. , 2006, Journal of colloid and interface science.

[7]  B. Berge,et al.  Electrowetting of water and aqueous solutions on poly(ethylene terephthalate) insulating films , 1996 .

[8]  C. Kim,et al.  Characterization of electrowetting actuation on addressable single-side coplanar electrodes , 2006 .

[9]  Craig Priest,et al.  Electrowetting of Aqueous Solutions of Ionic Liquid in Solid−Liquid−Liquid Systems , 2010 .

[10]  Craig Priest,et al.  Static and dynamic electrowetting of an ionic liquid in a solid/liquid/liquid system. , 2010, Journal of the American Chemical Society.

[11]  John Ralston,et al.  Contact angle saturation in electrowetting. , 2005, The journal of physical chemistry. B.

[12]  S. Rosselli,et al.  Biased-probe-induced water ion injection into amorphous polymers investigated by electric force microscopy , 2009 .

[13]  Shaun Berry,et al.  Engineering the electrocapillary behavior of electrolyte droplets on thin fluoropolymer films. , 2006, Langmuir : the ACS journal of surfaces and colloids.

[14]  P. Gennes.  Deposition of Langmuir-Blodgett layers , 1986 .

[15]  A. R. Blythe,et al.  Electrical properties of polymers , 1979 .

[16]  R. C. Weast.  CRC Handbook of Chemistry and Physics , 1973 .

[17]  J. Baret,et al.  Electrowetting: from basics to applications , 2005 .

[18]  A. Papathanasiou,et al.  Illuminating the connection between contact angle saturation and dielectric breakdown in electrowetting through leakage current measurementsa) , 2008 .

[19]  A. Amirfazli,et al.  Effects of an electric field on the surface tension of conducting drops , 2006 .

[20]  Ralph E. White,et al.  Comprehensive Treatise of Electrochemistry , 1981 .

[21]  R. Good,et al.  Contact angle, wetting, and adhesion: a critical review , 1992 .

[22]  Charles B. Duke,et al.  Molecular charge states and contact charge exchange in polymers , 1977 .

[23]  M. J. Sparnaay.  On the electrostatic contribution to the interfacial tension of semiconductor/gas and semiconductor/electrolyte interfaces , 1964 .

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

[25]  C. Kim,et al.  Frequency-Based Relationship of Electrowetting and Dielectrophoretic Liquid Microactuation , 2003 .

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

[27]  Thomas B. Jones,et al.  On the Relationship of Dielectrophoresis and Electrowetting , 2002 .

[28]  J. Andrade,et al.  Streaming potential investigations: Polymer thin films , 1981 .

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

[30]  Patrick Witomski,et al.  A proof of the invariance of the contact angle in electrowetting , 2007, Math. Comput. Model..

[31]  R. Fair,et al.  An integrated digital microfluidic lab-on-a-chip for clinical diagnostics on human physiological fluids. , 2004, Lab on a chip.

[32]  R. Horn,et al.  Electrowetting Measurements with Mercury Showing Mercury/Mica Interfacial Energy Depends on Charging , 2004 .

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

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

[35]  K. Nichols,et al.  Electrowetting-based microdrop tensiometer. , 2008, Langmuir : the ACS journal of surfaces and colloids.

[36]  W. Freyland.  Interfacial phase transitions in conducting fluids , 2007 .

[37]  N. Sato.  CHAPTER 10 – SEMICONDUCTOR PHOTOELECTRODES , 1998 .

[38]  John Ralston,et al.  Influence of the Electrical Double Layer in Electrowetting , 2003 .

[39]  Richard B. Fair,et al.  Digital microfluidics: is a true lab-on-a-chip possible? , 2007 .

[40]  Kwan Hyoung Kang,et al.  A numerical investigation on AC electrowetting of a droplet , 2008 .

[41]  D. Ende,et al.  Electrowetting of complex fluids: perspectives for rheometry on chip. , 2009, Langmuir : the ACS journal of surfaces and colloids.

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

[43]  B. Shapiro,et al.  Equilibrium behavior of sessile drops under surface tension, applied external fields, and material variations , 2003 .

[44]  J. Ralston,et al.  Dynamic Dewetting Regimes Explored , 2009 .

[45]  Andreas G. Boudouvis,et al.  Manifestation of the connection between dielectric breakdown strength and contact angle saturation in electrowetting , 2005 .

[46]  R. Good.  Surface free energy of solids and liquids: Thermodynamics, molecular forces, and structure , 1977 .

[47]  T. D. Blake,et al.  Wetting and Molecular Dynamics Simulations of Simple Liquids , 2008 .

[48]  P. Chudleigh.  Mechanism of charge transfer to a polymer surface by a conducting liquid contact , 1976 .

[49]  Françoise Brochard-Wyart,et al.  Dynamics of partial wetting , 1992 .

[50]  Daniel T. Chiu,et al.  Electrowetting-Induced Droplet Movement in an Immiscible Medium , 2003 .

[51]  F. Mugele.  Fundamental challenges in electrowetting: from equilibrium shapes to contact angle saturation and drop dynamics , 2009 .

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

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

[54]  A. W. Neumann,et al.  Techniques of Measuring Contact Angles , 1979 .

[55]  Camillo Cuvaj.  On Conservation of Energy in Electric Circuits , 1968 .

[56]  C. Werner,et al.  Electrokinetic Measurements Reveal Interfacial Charge at Polymer Films Caused by Simple Electrolyte Ions , 2001 .

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

[58]  P. Gennes,et al.  Capillarity and Wetting Phenomena , 2004 .

[59]  B. Widom.  Capillarity and Wetting Phenomena: Drops, Bubbles, Pearls, Waves , 2003 .

[60]  J. Bockris,et al.  Specific Adsorption of Ions , 1980 .

[61]  Philippe Dubois,et al.  Actuation potentials and capillary forces in electrowetting based microsystems , 2007 .

[62]  Stephan Herminghaus,et al.  Interface profiles near three-phase contact lines in electric fields. , 2003, Physical review letters.

[63]  R. Digilov,et al.  Charge-Induced Modification of Contact Angle: The Secondary Electrocapillary Effect , 2000 .