Abstract
Initiated by a task in tunable microoptics, but not limited to this application, a microfluidic droplet array in an upright standing module with 3 × 3 subcells and droplet actuation via electrowetting is presented. Each subcell is filled with a single (of course transparent) water droplet, serving as a movable iris, surrounded by opaque blackened decane. Each subcell measures 1 × 1 mm2 and incorporates 2 × 2 quadratically arranged positions for the droplet. All 3 × 3 droplets are actuated synchronously by electrowetting on dielectric (EWOD). The droplet speed is up to 12 mm/s at 130 V (Vrms) with response times of about 40 ms. Minimum operating voltage is 30 V. Horizontal and vertical movement of the droplets is demonstrated. Furthermore, a minor modification of the subcells allows us to exploit the flattening of each droplet. Hence, the opaque decane fluid sample can cover each water droplet and render each subcell opaque, resulting in switchable irises of constant opening diameter. The concept does not require any mechanically moving parts or external pumps.
Highlights
Nowadays, technological progress is often inseparably linked to the miniaturization of electrical, mechanical, and optical components
A minor modification of the subcells allows us to exploit the flattening of each droplet
All droplets are moved synchronously to one of their 2 × 2 possible droplet positions depicted in Figure 2, due to the specific described electrode structure
Summary
Technological progress is often inseparably linked to the miniaturization of electrical, mechanical, and optical components. Other developments are aimed at bringing complete chemical laboratory processes to the size of a chip. These socalled lab-on-a-chip devices allow for automatic analyses of small liquid samples [3]. In conventional lab chips continuous fluid flows are handled in microchannels. The degree of freedom of the fluid flow is small. The functionality is completely determined by the chip design and prohibits alteration during operation. An alternative approach is made up of lab-on-a-chip devices for droplet manipulation (digital microfluidics, lab-on-a-chip 2.0). The droplets have volumes of a few pl to a few μl and can be moved more or less freely on the chip [4]
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