Reports the completion of four fundamental fluidic operations considered essential to build digital microfluidic circuits, which can be used for lab-on-a-chip or micro total analysis system (/spl mu/TAS): 1) creating, 2) transporting, 3) cutting, and 4) merging liquid droplets, all by electrowetting, i.e., controlling the wetting property of the surface through electric potential. The surface used in this report is, more specifically, an electrode covered with dielectrics, hence, called electrowetting-on-dielectric (EWOD). All the fluidic movement is confined between two plates, which we call parallel-plate channel, rather than through closed channels or on open surfaces. While transporting and merging droplets are easily verified, we discover that there exists a design criterion for a given set of materials beyond which the droplet simply cannot be cut by EWOD mechanism. The condition for successful cutting is theoretically analyzed by examining the channel gap, the droplet size and the degree of contact angle change by electrowetting on dielectric (EWOD). A series of experiments is run and verifies the criterion.

Creating, transporting, cutting, and merging liquid droplets by electrowetting-based actuation for digital microfluidic circuits

A microactuator for rapid manipulation of discrete microdroplets is presented. Microactuation is accomplished by direct electrical control of the surface tension through two sets of opposing planar electrodes fabricated on glass. A prototype device consisting of a linear array of seven electrodes at 1.5 mm pitch was fabricated and tested. Droplets (0.7–1.0 μl) of 100 mM KCl solution were successfully transferred between adjacent electrodes at voltages of 40–80 V. Repeatable transport of droplets at electrode switching rates of up to 20 Hz and average velocities of 30 mm/s have been demonstrated. This speed represents a nearly 100-fold increase over previously demonstrated electrical methods for the transport of droplets on solid surfaces.

/pdf/electrowetting-based-actuation-of-liquid-droplets-for-1ugwu9gp77.pdf

Electrowetting-based actuation of liquid droplets for microfluidic applications

The serviceability of microfluidics-based instrumentation including ‘lab-on-a-chip’ systems critically depends on control of fluid motion. We are reporting here an alternative approach to microfluidics based upon the micromanipulation of discrete droplets of aqueous electrolyte by electrowetting. Using a simple open structure, consisting of two sets of opposing planar electrodes fabricated on glass substrates, positional and formational control of microdroplets ranging in size from several nanoliters to several microliters has been demonstrated at voltages between 15–100 V. Since there are no permanent channels or structures between the plates, the system is highly flexible and reconfigurable. Droplet transport is rapid and efficient with average velocities exceeding 10 cm s−1 having been observed. The dependence of the velocity on voltage is roughly independent of the droplet size within certain limits, thus the smallest droplets studied (∼3
nl) could be transported over 1000 times their length per second. Formation, mixing, and splitting of microdroplets was also demonstrated using the same microactuator structures. Thus, electrowetting provides a means to achieve high levels of functional integration and flexibility for microfluidic systems.

/pdf/electrowetting-based-actuation-of-droplets-for-integrated-40opppn1w3.pdf

Electrowetting-based actuation of droplets for integrated microfluidics

Films whose water contact angle is higher than 150° have been the subject of great interest and enthusiastic study in recent years. These films, which are called super-hydrophobic, are fabricated by combining appropriate surface roughness with surfaces of low surface energy. Here we briefly review the fundamental theories on the wettability of a hydrophobic rough solid surface, together with recent works on the processing and properties of super-hydrophobic films. Though the practical application of these films is still limited, the obstacles to application are gradually being surmounted, providing a great opportunity for the development of various industrial products.

Recent Studies on Super-Hydrophobic Films

This article discusses and experimentally verifies how to lower the operating voltage that drives liquid droplets by the principle of electrowetting on dielectric (EWOD). A significant contact angle change (120°→80°) is desired to reliably pump the droplet in microchannels for applications such as lab-on-a-chip or micrototal analysis systems. Typically, much higher voltages (>100 V) are used to change the wettability of an electrolyte droplet on a dielectric layer compared with a conductive layer. The required voltage can be reduced by increasing the dielectric constant and decreasing the thickness of the dielectric layer, thus increasing the capacitance of the insulating layer. This dependence of applied voltage on dielectric thickness is confirmed through EWOD experiments for three different dielectric materials of varying thickness: Amorphous fluoropolymer (Teflon® AF, Dupont), silicon dioxide (SiO2) and parylene. The dependence on the dielectric constant is confirmed with two different dielectric mate...

Low voltage electrowetting-on-dielectric

Electrowetting of water and aqueous solutions on poly(ethylene terephthalate) insulating films

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Electrowetting of water and aqueous solutions on poly(ethylene terephthalate) insulating films