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DEP MICROACTUATION OF

LIQUIDS

Date 　 ： 2012/11/05

Name 　： Po Yuna Cheng

Teacher ： Professor Hsu

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OutlineABSTRACT

INTRODUCTION

NANOLITER DROPLET GENERATION

DISCUSSION

CONCLUSION

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ABSTRACTWe report rapid actuation of nanoliter to microliter water volumes using the dielectrophoretic (DEP) force. This microelectromechanical mechanism for manipulating, transporting,and metering liquids harnesses strong, non-uniform rf electric fields created by co-planar electrodes with 30 to 100 um feature size pattemed on insulating substrates. Electrolysis is avoided by spin-coating the electrodes with 10 um of polyimide. Transient liquid velocities exceed 25 cm/s, and droplets down to a few nanoliters in volume are formed in <30 ms. Because water responds rapidly, controlled DEP actuation can be achieved by very short bursts of rf voltage. An important benefit of minimized exposure of conductive liquids to strong rf fields is reduced Joule heating. A new microfluidic scheme for the "lab on a chip" is proposed, based on high-speed,programmable manipulation of discrete nanodroplets on smooth substrates.

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To realize the "lab on a chip", micro-fluidicsystems are needed to control and manipulate small liquid inventories.

Schemes for this purpose include micro-channels that exploit microcapillarity, electrophoretic and electroosmotic pumping, and voltage- or light-mediated surface wetting. In contrast to these, liquid DEP exploits the ponderomotive force to create hydrostatic equilibria, where dielectric liquids are configured by non-uniform electric fields.The dielectrophoretic force attracts dielectrics includingliquids to regions of strong electric field.

INTRODUCTION

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Figure 1. Co-planar strips terminated in semi-circular electrodes for droplet formation.

(a)Voltage off; initial ~10 uliter droplet at right.

(b) Voltage on; finger has reachedsemi-circular electrodes at left.

(c) Voltage off; isolated ~60 nanoliter droplet at left; flow structure is completely drained.

NANOLITER DROPLET GENERATION

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Figure 2. Multiple droplet generation structure with initiallydeposited -3 pl droplet at right.

(a)Rf field off

(b) Field on;droplet is distorted.

(c) Field on: finger has reuched end ofstructure at left.

(d) Field on: liquid is pinching offbetween each of the circles.

(e) Field off: 4 hemispherical droplets -4 nanoliters in volume are formed.

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DISCUSSION

發現一個問題，由實驗報告顯示，驅動 DEP 所需要的電壓已經過高，而降低電壓的方法，建議使用較薄的介質鍍膜在電極上。

降低的電壓的第二種方式是，減少的特徵尺寸的電極的結構，特別是電極間的間距。在降低的間距從本 30 微米~10 微米，甚至更小。

稀釋劑聚酰亞胺塗料已經嘗試過，但效果不理想，可能原因是由於使用旋轉塗佈的程序中出問題。

保持良好的介電極強度和控制表面的潤濕性能為雙重引響因素。

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CONCLUSIONUsing DEP, we have demonstrated field-mediated formation of multiple droplets of volume ~4 nano-liters in less than ~30 milliseconds. The "nanodroplet switchyard" scheme represents a unique version of the "lab on a chip". First of all, the open, planar structures are easy to fabricate and clean. They might also be cheap enough to be disposable. There will be no problems associated with leakage, priming, or clogging. Using the strategy of dividing the samples into discrete droplets, there should be little likelihood of inter-sample mixing or crosscontamination, an important consideration in the case of critical processes and biological assay protocols.

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Thank you for your attention