ELECTROWETTING
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30-01-2009, 03:58 PM


The term electrowetting was first introduced in 1981 to describe an effect proposed for designing a new type of display device [G. Beni and S. Hackwood, Appl. Phys. Lett. 38, 4, pp.207-209, 1981]. The electrowetting effect was originally defined as "the change in solid electrolyte contact angle due to an applied potential difference between the solid and the electrolyte". Electrowetting is akin to but distinct from electrocapillarity. In the past 25 years or so a large number of devices based on electrowetting have been devised. In particular, electrowetting has recently been used successfully as one of several techniques used to actuate microdroplets in a digital microfluidic device. Electrowetting is essentially a phenomenon whereby an electric field can modify the wetting behavior of a droplet in contact with an insulated electrode. If an electric field is applied non-uniformly then a surface energy gradient is created which can be used to manipulate a droplet sandwiched between two plates. Electrowetting arrays allow large numbers of droplets to be independently manipulated under direct electrical control without the use of pumps, valves or even fixed channels. Electrowetting is now used in a wide range of applications from modulab to adjustable lenses and electronic displays.
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vincyvs
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05-08-2009, 11:01 AM

hiiiiiiiiiiiiiiiiii,cute
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prockzg
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27-06-2010, 02:27 PM

plz send me more information & abtract about this topic
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27-06-2010, 02:41 PM

plz send me more inf abt this topic
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29-06-2010, 07:21 PM

Electrowetting
It s the modification of the wetting properties of a hydrophobic surface with an applied electric field. Gabriel Lippmann in 1875 explained the electrowetting behavior of mercury and other liquids.

Electrowetting theory
The formal definition of this effect is : "the change in solid-electrolyte contact angle due to an applied potential difference between the solid and the electrolyte" . the electrolyte droplet is pulled down onto the electrode by the fringing field at its corners thereby contact angle and increasing the droplet contact area. he energy stored in the capacitor formed between the conductor and the electrolyte adds to the Gibbs free energy raising it. the surface tension of an interface has an alternate definition that "it is the Gibbs free energy required to create a certain area of that surface". Thus when the Gibbs free energy surface tension changes accordingly.
This behaviour is better explained by the thermodynamic model. It gives a equation governing the the dependence of contact angle on the effective applied voltage as.

Materials
Only some surfaces show the theoretically predicted electrowetting behavior whose reasons are still being researched. Amorphous fluoropolymers form the best electrowetting materials. appropriate patterning can enhance their behaviour.

Applications
-adjustable lenses
-electronic displays
-modulab
-switches for optical fibers.

for full details , refer these:
en.wikipediawiki/Electrowetting
users.monash.edu.au/~lyeo/Dr_Leslie_Yeo/Publications_files/Yeo_Electrowetting_Encyclopedia%20of%20Microfluidics%20and%20Nanofluidics.pdf
doc.utwente.nl/54091/1/electrowetting.pdf
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22-01-2012, 02:52 PM

pleaes send me the seminar and presentation report of electrowetting ...
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23-01-2012, 11:35 AM

to get information about the topic ELECTROWETTING full report,ppt, related topic refer the link bellow

topicideashow-to-electrowetting--1083

topicideashow-to-electrowetting

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09-04-2012, 01:12 PM

ELECTROWETTING



.docx   SEMINAR ON ELECTROWETTING.docx (Size: 1.14 MB / Downloads: 32)

INTRODUCTION
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".
Electrowetting is the modification of the wetting properties of a hydrophobic surface with an applied electric field.
Electrowetting is a microfluidic phenomena that is currently enjoying explosive growth as a driving mechanism for a wide range of fluidic and electro-optic applications.
Electrowetting involves modifying the surface tension of liquids on a solid surface using a voltage. By applying a voltage, the wetting properties of a hydrophobic surface can be modified and the surface becomes increasingly hydrophilic (wettable).
The electrowetting behavior of mercury and other liquids on variably charged surfaces was probably first explained by GABRIEL LIPPMANN in 1875 and was certainly observed much earlier. Froumkin used surface charge to change the shape of water drops in 1936.


THEORY OF ELECTROWETTING
Moving the wetted interface between a dielectric liquid and an insulated flat, overcoating a conducting surface, is important for micro-fluidics, ink jet printing and lab on a chip designs. In this talk, electro-wetting is analyzed using reversible, thermodynamic energy balances to obtain the voltage versus charge relations on lines of isothermal, constant interfacial surface energy. The very close connection between linear elastic fracture mechanics (LEFM) and general energy balances in charged systems is exploited to understand electro-wetting systems: it is found that the heat released during charging of an isothermal, aquatic dielectric is 140% larger than the electrical work in a linear capacitor system at room temperature! The stability of linear systems is studied in quite a bit of detail. It is shown that a parallel plate capacitor whose capacitance changes linearly with wetted surface area is neutrally stable at constant voltage and absolutely stable at constant charge similar to a constant K specimen in LEFM. The charged dielectric at the contact where the electro-wetted interface advances, like the crack tip in LEFM, is poorly understood. The charge added to an electro-wetting system is proportional to the total wetted surface area so the current is proportional to the areal velocity of the interface. Controlled wetting for constant charge and voltage systems in electro-capillary lines are investigated in some detail.

MATERIALS USED
Going into the kitchen and doing a small experiment: placing a drop of water on a smooth, clean glass surface (a plate, for example), and another drop on a Teflon frying pan or on greased baking paper. It is seen that there is the difference in the behavior of the drops: on the glass the drop flattens out whereas on the Teflon or the greased paper it turns into a ball. We say the drop wets the glass, whereas on a hydrophobic (‘‘water hating’’) surface such as Teflon the wetting is only partial.


APPLICATIONS OF ELECTROWETTING
Electrowetting is now used in a wide range of applications from modular to adjustable lenses, electronic displays (e-paper) and switches for optical fibers. 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.


LIQUID LENSES-
Water is a polar liquid. Thus its molecules can be attracted by an electric field. It is thus possible to change the shape of the liquid drop.
To carry out this process of electrowetting a water drop is deposited on a substrate made of metal, covered by a thin insulating layer. The voltage applied to the substrate modifies the contact angle of the liquid drop. The liquid lens uses two isodensity liquids, one is an insulator while the other is a conductor. The variation of voltage leads to a change of curvature of the liquid-liquid interface, which in turn leads to a change of the focal length of the lens.



WETTING DYNAMICS:-
Its ability to change a droplet’s shape from its equivalent configuration with a fast control parameter (the electrostatic field) , electrowetting is suitable for dynamic aspects of wetting. Capacitive measurements provide contact angle values in a much more rapid and automatable way than direct image methods, making a performant tool for dynamic measurement.

OIL IN WATER ELECTROWETTING:-

Wetting of oil droplets in a water environment is a very promising system as it presents weak hysteresis, allowing creation of flat wetting defects controlled by a local field to study additional hysteresis. It should also allow de-wettting transitions controlled by a electric field , for initial total wetting .

MICROELECTROMECHANICAL DEVICES:-

Microactuation provides a golden opportunity for the application of electrowetting , which has just been realized. We are aware of 3 examples :-
a) A mercury droplet follows a potential drop (continuous electrowetting) in an electrolyte solution, its movement dragging a micromotor.
b) Microlabs in which aqueous solution droplets move possibly mix in an oil environment on paths made from electrically isolated electrodes.


CONCLUSION and FUTURE ASPECTS

A wide range of superhydrophobic surfaces have now been reported and are reviewed here. Most experiments show a contact angle reduction from θ_S ∼ 160° to θ_V ∼ 100° and a very limited intrinsic reversibility of ∼10–20°. Simply achieving
the irreversible Wenzel state could be of use for applications such as infusing polar epoxies into fiber reinforcements for the creation of composite materials. If improved reversibility is desired, then there are likely numerous structures that have yet to be investigated. Structures for improved reversibility might be inspired by recent work on creating superhydrophobic surfaces on materials that exhibit a hydrophilic.


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