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| '''Electrowetting''' is the modification of the [[wetting]] properties of a surface (which is typically [[hydrophobic]]) with an applied [[electric field]]. | | I woke up yesterday and realized - I've been single for a while at the moment and following much intimidation from friends I now find myself signed-up for internet dating. They assured me that there are plenty of pleasant, normal and entertaining visitors to meet up, where can i buy luke bryan tickets ([http://www.museodecarruajes.org check this link right here now]) so the pitch is gone by here!<br>My household and buddies are awesome and hanging out with them at [http://www.guardian.co.uk/search?q=bar+gigs bar gigs] or dishes is constantly a necessity. I have never been into clubs as I find that you can not have [http://lukebryantickets.lazintechnologies.com About Luke Bryan] a nice dialogue together with the noise. Additionally, I got two really adorable and definitely cheeky canines that are always excited to meet new people.<br>I strive to keep as toned as possible [https://Www.Google.com/search?hl=en&gl=us&tbm=nws&q=staying staying] at the gym many times per week. I love my athletics and attempt to perform or see as numerous a possible. I will often at Hawthorn suits being wintertime. Notice: I've observed the carnage of wrestling suits at stocktake sales, In case [http://lukebryantickets.pyhgy.com vip tickets for luke bryan] that you really considered purchasing a sport I really do not mind.<br><br>My blog post [http://www.banburycrossonline.com vip tickets To Luke bryan] |
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| ==History==
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| The electrowetting behavior of [[mercury (element)|mercury]] and other [[liquid]]s on variably charged surfaces was probably first explained by [[Gabriel Lippmann]] in 1875<ref>M.G. Lippmann,"Relation entre les phénomènes électriques et capillaires." Ann. Chim. Phys, 5:494, 1875</ref> and was certainly observed much earlier. [[Alexander Frumkin|A.N. Frumkin]] used surface charge to change the shape of [[water]] drops in 1936.<ref>A. Frumkin, Об явлениях смачивания и прилипания пузырьков, I (On the phenomena of wetting and adhesion of the bubbles, I). Zhurnal Fizicheskoi Khimii (J Phys Chem USSR),12: 337- 345 (1938).</ref> The term electrowetting was first introduced in 1981 to describe an effect proposed for designing a new type of display device.<ref>[[Gerardo Beni|G. Beni]] and [[Susan Hackwood|S. Hackwood]], Appl. Phys. Lett. 38, 4, pp.207-209, 1981</ref> The use of a "fluid transistor" for manipulating chemical and biological fluids was first investigated by J. Brown in 1980 and later funded in 1984-1988 under NSF Grants 8760730 & 8822197,<ref>[http://www.nsf.gov/awardsearch/piSearch.do;jsessionid=D05E82394F781CBA17DB0C5AC8E3C0B8?SearchType=piSearch&page=1&QueryText=&PIFirstName=james&PILastName=brown&PIInstitution=cytonix&PIState=MD&PIZip=&PICountry=US&RestrictExpired=on&Search=Search#results]</ref> employing insulating dielectric and hydrophobic layers, immiscible fluids, DC or RF power; and mass arrays of miniature interleaved electrodes with large or matching [[Indium tin oxide]] (ITO)
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| electrodes to digitally relocate nano droplets in linear, circular and directed paths, pump or mix fluids, fill reservoirs and control fluid flow electronically or optically.<ref>[http://www.cytonix.com/US%20Patent%206143496%20.pdf]</ref>
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| Electrowetting using an insulating layer on top of the bare electrodes was later studied by Bruno Berge in 1993.<ref>B. Berge, "Électrocapillarité et mouillage de films isolants par l'eau", C.R. Acad. Sci. Paris, t. 317, Série II, p. 157-163, 1993.</ref> Electrowetting on this dielectric-coated surface is called electrowetting-on-dielectric (EWOD)<ref name="ReferenceA">J. Lee, "Microactuation by Continuous Electrowetting and Electrowetting: Theory, Fabrication, and Demonstration," PhD Thesis, University of California, Los Angeles, 2000</ref> to distinguish it from the conventional electrowetting on the bare electrode. Microfluidic manipulation of liquids by electrowetting was demonstrated first with mercury droplets in water<ref>J. Lee and C.-J. Kim, "Liquid Micromotor Driven by Continuous Electrowetting", Proc. IEEE Micro Electro Mechanical Systems Workshop, Heidelberg, Germany, Jan. 1998, pp. 538-543</ref> and later with water in air<ref name="ReferenceA"/> and water in oil.<ref>M.G. Pollack, R.B. Fair and A.D. Shenderov, "Electrowetting-based actuation of liquid droplets for microfluidic applications", Applied Physics Letters, vol. 77 (11), 2000</ref> Manipulation of droplets on a two-dimensional path was demonstrated later.<ref>S.-K. Fan, P.-P. de Guzman, and C.-J. Kim, "EWOD Driving of Droplet on NxM Grid Using Single-Layer Electrode Patterns, Tech. Dig., Solid-State Sensor, Actuator, and Microsystems Workshop, Hilton Head Island, SC, June 2002, pp. 134-137</ref><ref>J. Gong and C.-J. Kim, "Two-Dimensional Digital Microfluidic System by Multi-Layer Printed Circuit Board", Proc. IEEE Conf. MEMS, Orlando, FL, Jan. 2005, pp. 726-729</ref>
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| If the liquid is discretized and programmably manipulated, the approach is called "Digital Microfluidic Circuits"<ref>C.-J. Kim, "Integrated Digital Microfluidic Circuits Operated by Electrowetting-on-Dielectrics (EWOD) Principle", granted in 2000 by Defense Advanced Research Projects Agency (DARPA), award number N66001-0130-3664</ref><ref>C.-J. Kim, "Micropumping by Electrowetting", Proceedings of the ASME International Mechanical Engineering Congress and Exposition, November 2001, New York, NY, IMECE2001/HTD-24200.</ref> or "Digital Microfluidics".<ref>M.G. Pollack, Electrowetting-Based Microactuation Of Droplets For Digital Microfluidics, PhD Thesis, Duke University, 2001.</ref> Discretization by electrowetting-on-dielectric (EWOD) was first demonstrated by Cho, Moon and Kim,<ref>S. K. Cho, H. Moon, and C.-J Kim, "Creating, Transporting, Cutting, and Merging Liquid Droplets by Electrowetting-Based Actuation for Digital Microfluidic Circuits", J. Microelectromechanical Systems, Vol. 12, 2003, pp. 70-80</ref> completing the four basic digital microfluidic functions of creating, transporting, dividing and merging droplets on chip by electrowetting
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| Since then, a large number of applications based on electrowetting have been demonstrated. Currently five companies are at the forefront in commercializing electrowetting-based applications based on [[Cytonix]]<ref>[http://www.cytonix.com/US%20Application%2020080169184.pdf]</ref> and Berge's later research: Clinical diagnostics by Advanced Liquid Logic<ref>[http://www.liquid-logic.com Advanced Liquid Logic]</ref> which was spun out of Duke University, electronic paper by both Gamma Dynamics,<ref>[http://www.gammadynamics.net Gamma Dynamics]</ref> which was spun out of the University of Cincinnati, and [[Liquavista]]<ref>[http://www.liquavista.com LiquaVista]</ref> which was spun out of Philips Research, liquid lenses by [http://www.varioptic.com Varioptic],<ref>[http://www.varioptic.com Varioptic]</ref> and [[Digital PCR]] by [[Life Technologies]] and [[Sequenom]]. In some of these applications, electrowetting allows large numbers of droplets to be independently manipulated under direct electrical control without the use of external pumps, valves or even fixed channels. In e-paper and liquid lenses, droplets are manipulated in-place whereas in clinical diagnostics applications, droplets are moved around on the platform.
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| == Electrowetting theory ==
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| [[File:Electrowetting (svg).svg|thumb|300px|Liquid, Isolator, Substrate]]
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| The electrowetting effect has been defined as "the change in solid-[[electrolyte]] [[contact angle]] due to an applied [[potential difference]] between the solid and the electrolyte". The phenomenon of electrowetting can be understood in terms of the forces that result from the applied electric field.<ref name=Chang>{{cite book | author=Chang, H.C., Yeo, L. | title=Electrokinetically Driven Microfluidics and Nanofluidics | year=2009 | publisher =[[Cambridge University Press]] }}</ref><ref name=Kirby>{{cite book | author=Kirby, B.J. | title=Micro- and Nanoscale Fluid Mechanics: Transport in Microfluidic Devices.| url=http://www.kirbyresearch.com/textbook| year=2010| publisher=Cambridge University Press| isbn=978-0-521-11903-0}}</ref> The fringing field at the corners of the electrolyte droplet tends to pull the droplet down onto the electrode, lowering the macroscopic contact angle and increasing the droplet contact area. Alternatively, electrowetting can be viewed from a thermodynamic perspective. Since the surface tension of an interface is defined as the [[Gibbs free energy]] required to create a certain area of that surface, it contains both chemical and electrical components, and charge becomes a significant term in that equation. The chemical component is just the natural surface tension of the solid/electrolyte interface with no electric field. The electrical component is the energy stored in the [[capacitor]] formed between the conductor and the electrolyte.
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| The simplest derivation of electrowetting behavior is given by considering its thermodynamic model. While it is possible to obtain a detailed numerical model of electrowetting by considering the precise shape of the electrical fringing field and how it affects the local droplet curvature, such solutions are mathematically and computationally complex. The thermodynamic derivation proceeds as follows. Defining the relevant surface tensions as:
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| :<math> \gamma_{ws} \,</math> - The total, electrical and chemical, surface tension between the electrolyte and the conductor
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| :<math> \gamma_{ws}^0 \,</math> - The surface tension between the electrolyte and the conductor at zero electric field
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| :<math> \gamma_s \,</math> - The surface tension between the conductor and the external ambient
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| :<math> \gamma_w \,</math> - The surface tension between the electrolyte and the external ambient
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| :<math> \theta</math> - The macroscopic contact angle between the electrolyte and the dielectric
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| :<math>C </math> - The capacitance of the interface, є<sub>r</sub>є<sub>0</sub>/t, for a uniform dielectric of thickness t and permittivity є<sub>r</sub>
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| :<math>V </math> - The effective applied voltage, integral of the electric field from the electrolyte to the conductor
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| Relating the total surface tension to its chemical and electrical components gives:
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| :<math> \gamma _{ws} = \gamma _{ws}^0 - \frac{CV^2}{2} \,</math>
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| The [[contact angle]] is given by the Young-Dupre equation, with the only complication being that the total surface energy <math> \gamma_{ws}</math> is used:
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| :<math> \gamma_{ws} = \gamma_s - \gamma_w \cos(\theta) \,</math>
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| Combining the two equations gives the dependence of θ on the effective applied voltage as:
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| :<math> \cos \theta = \left(\frac{\gamma_s - \gamma _{ws}^0 +\frac{CV^2}{2}}{\gamma_w}\right) \,</math>
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| An additional complication is that liquids also exhibit a saturation phenomenon: after certain voltage, the saturation voltage, the further increase of voltage will not change the contact angle, and with extreme voltages the interface will only show instabilities.
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| However, surface charge is but one component of surface energy, and other components are certainly perturbed by induced charge. So, a complete explanation of electrowetting is unquantified, but it should not be surprising that these limits exist.
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| It was recently shown<ref>[http://arxiv.org/abs/1102.0791 A Model of Electrowetting, Reversed Electrowetting and Contact Angle Saturation. Dan Klarman, David Andelman, Michael Urbakh]</ref> that contact angle saturation can be explained if electrowetting is observed as a global phenomenon affected by the detailed geometry of the system. Within this framework it is predicted that reversed electrowetting is also possible (contact angle grows with the voltage).
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| It has also been experimentally shown by Chevaloitt <ref>[http://www.ece.uc.edu/devices/Downloads/Documents/Publications/Experimental%20Validation%20of%20the%20Invariance%20of%20Electrowetting_New.pdf Experimental Validation of the Invariance of Electrowetting Contact Angle Saturation]</ref> that contact angle saturation is invariant to all materials parameters, thus revealing that a universal theory for saturation is still lacking, and that when good materials are utilized, most saturation theories are invalid. This same paper further suggests that electrohydrodynamic instability may be the source of saturation, a theory that is unproven but being suggested by several other groups as well.
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| == Reverse electrowetting == | |
| [[Reverse electrowetting]]<ref>[http://www.nature.com/ncomms/journal/v2/n8/full/ncomms1454.html?WT.ec_id=NCOMMS-201108 T. Krupenkin and J.A.Taylor , ''Nature Comms. Rep.'' '''2''', 448, (2011).]</ref> can be used to harvest energy via a mechanical-to-electrical engineering scheme.
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| == Photoelectrowetting ==
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| [[Photoelectrowetting]]<ref>[http://www.nature.com/srep/2011/111207/srep00184/full/srep00184.html S. Arscott, ''Sci. Rep.'' '''1''', 184, (2011). Scientific Reports: Nature Publishing Group.]</ref> can be observed if the conductor in the liquid/insulator/conductor stack used for electrowetting is replaced by a [[semiconductor]]. By optically modulating the number of carriers in space-charge region of the semiconductor, the contact angle of a liquid droplet can be altered in a continuous way. This effect can be explained by a modification of the Young-Lippmann equation.
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| == Materials ==
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| For reasons that are still under investigation, only a limited set of surfaces exhibit the theoretically predicted electrowetting behavior. Amorphous [[fluoropolymers]] are by far the best electrowetting materials discovered so far, and it has been found that their behaviour can be enhanced by the appropriate patterning. Three types of such polymers are commercially available: FluoroPel hydrophobic and superhydrophobic V-series polymers are sold by [[Cytonix]], CYTOP is sold by [[Asahi Glass Co.]], and Teflon AF is sold by [[DuPont]].
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| == Applications ==
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| Electrowetting is now used in a wide range of [http://www.varioptic.com/en/topmenu/liquid-lens-technology.html applications] from modular to adjustable lenses, electronic displays ([[e-paper]]) and switches for optical fibers. Electrowetting has recently been evoked for manipulating Soft Matter particularly, suppressing [[coffee stain]] effect.<ref name="ERAL1">[http://pubs.rsc.org/en/content/articlelanding/2011/sm/c1sm05183k H.Burak Eral, D.Mampallil, F.Mugele "Suppressing the coffee stain effect: how to control colloidal self-assembly in evaporating drops using electrowetting", Soft Matter, 2011, 7, 4954-4958, ] {{doi|10.1039/C1SM05183K}}</ref> Furthermore, filters with Electrowetting functionality has been suggested for cleaning oil spills and separating oil-water mixtures.<ref name="ERAL2">[http://pubs.rsc.org/en/Content/ArticleLanding/2011/SM/c0sm01403f H.Burak Eral, R.Ruiter, J.Ruiter, J.M.Oh, C.Semprebon, M.Brinkmann, F.Mugele, "Reversible morphological transitions of a drop on a fiber", Soft Matter, 2011, 7 (11), 5138 - 5143, ] {{doi|10.1039/C0SM01403F}}</ref>
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| == International meeting ==
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| An international meeting for electrowetting is held every two years. The next meeting is in 2014 in Cincinnati, USA: http://secs.ceas.uc.edu/electrowetting2014/
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| The previous hosts of the electrowetting meeting are: Mons (1999), Eindhoven (2000), Grenoble (2002), Blaubeuren (2004), Rochester (2006), Los Angeles (2008), Pohang (2010), and Athens (2012).
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| == See also ==
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| * [[Microfluidics]]
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| ==References==
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| {{reflist}}
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| ==External links==
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| * [http://fan-tasy.org/ Fan-TASY Lab at National Taiwan University]
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| * [http://www.chem.utoronto.ca/staff/WHEELER/ Wheeler Digital Microfluidics Group] at the University of Toronto
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| * [http://www.ece.uc.edu/devices/ Electrowetting at the University of Cincinnati.]
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| * [http://www.ee.duke.edu/research/microfluidics/ Digital Microfluidics at Duke University]
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| * [http://pcf.tnw.utwente.nl/ Physics of Complex Fluids at University of Twente]
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| * [http://www.kruss.de/en/newsletter/newsletter-archives/2006/issue-12/news.html#c5087 Diagram explaining electrowetting]
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| * [http://www.printedelectronicsworld.com/articles/progress_with_electrowetting_displays_00001461.asp?sessionid=1 Progress with electrowetting displays]
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| * [http://www.nanolab.uc.edu/ Electrowetting flexible display at UC NanoLab, University of Cincinnati]
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| *[http://www.youtube.com/watch?v=mr5m3NVtZzg&feature=related Liquidvista Low Frequency Electrowetting 6.2-inch Display]
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| [[Category:Display technology]]
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