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Advancing the Frontiers of Low Voltage Electrowetting on Dielectrics through a Complete Understanding of Three Phases System Interactions

Chevalliot, St¿¿¿¿phanie

Abstract Details

2012, PhD, University of Cincinnati, Engineering and Applied Science: Materials Science.

Electrowetting on dielectrics (EWOD) has recently received a significant interest mainly due to its ability to rapidly manipulate small volumes of fluids. Electrowetting controls the wetting of a liquid at an interface with a solid by application of electromechanical force. It is promising for numerous applications, ranging from adaptive lens systems to lab-on-chip devices, as well as electronic displays.

While several EWOD-based products have already been commercialized, numerous challenges still have to be addressed, in order to fully exploit the potential of the electrowetting technology. The practically most important and least understood limitation of electrowetting is the saturation of contact angle, preventing complete wetting. Another significant issue encountered with EWOD is the lack of diversity of conducting fluids (mainly aqueous fluids have been investigated until now). In addition, the voltages required to obtain significant contact angle changes need to be dramatically reduced, in order to make the electrowetting technique useful for portable applications. Finally, the reliability of EWOD devices has to be improved, to enable further commercialization. In particular, factors affecting dielectric failure (through charging or breakdown) should be identified.

This thesis is dedicated to understand the interactions between the three phases of EWOD systems (dielectric material, electrowetting fluid with ionic content and insulating fluid), in order to solve the four problems previously described and thus advance the frontiers of reliable and low-voltage electrowetting.

In this dissertation, it is revealed that for DC driving there exists a contact angle at complete saturation that is invariant to multiple dielectric materials and fluids parameters. The experimental results refute most of the proposed hypotheses for explaining saturation. Furthermore, it is established that saturation is a time-dependent phenomenon, with different physical mechanisms dominating its behavior over different time scales. A new theory for electrowetting saturation is proposed: micro-droplet ejection through “Taylor saturation”.

The successful use of polar non-aqueous solvents to replace water for electrowetting applications is also reported. It is shown that with a careful selection of ionic content and a good solvent/oil match (high interfacial tension), electrowetting behaviors comparable to those of aqueous solutions can be achieved, while limiting or even eliminating the risk of dielectric failure. Non-aqueous fluids are also demonstrated as fully effective in EWOD-based display pixels.

Furthermore, it is proved that ion penetration is the cause of dielectric failure. Increasing the crystallinity of Parylene C (one of the most commonly used dielectric for EWOD applications) did not appear to impact the resistance of the material toward breakdown, whereas multi-layer insulator stacking revealed an efficient method to prevent system failure.

These findings advance environmental robustness and reliability issues for the commercialization of electrowetting devices.

Vikram Kuppa, PhD (Committee Chair)
F James Boerio, PhD (Committee Member)
Relva Buchanan, ScD (Committee Member)
Jason Heikenfeld, PhD (Committee Member)
133 p.

Recommended Citations

Citations

  • Chevalliot, S. (2012). Advancing the Frontiers of Low Voltage Electrowetting on Dielectrics through a Complete Understanding of Three Phases System Interactions [Doctoral dissertation, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1337888430

    APA Style (7th edition)

  • Chevalliot, St¿¿¿¿phanie. Advancing the Frontiers of Low Voltage Electrowetting on Dielectrics through a Complete Understanding of Three Phases System Interactions. 2012. University of Cincinnati, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1337888430.

    MLA Style (8th edition)

  • Chevalliot, St¿¿¿¿phanie. "Advancing the Frontiers of Low Voltage Electrowetting on Dielectrics through a Complete Understanding of Three Phases System Interactions." Doctoral dissertation, University of Cincinnati, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1337888430

    Chicago Manual of Style (17th edition)