Electrowetting on gold electrodes with microscopic three-dimensional structures for microfluidic devices

Abstract

To improve the performance of electrowetting-based microfluidic devices, we used micropillar structures to enhance the changes in the wettability of gold electrodes. The changes in the contact angle of a sessile drop were influenced by the diameter of the micropillars and interpillar distances. For a potential change between 0 V and −1.0 V, the change of the contact angle of the KCl sessile drop was 41°on a smooth electrode, but 88°on an electrode with micropillars with a 10 m diameter. Furthermore, the existence of the micropillars accelerated the change of the contact angle. The gold electrodes with the micropillars were used to generate the capillary force to mobilize a liquid column in a microflow channel. Compared to a device with a smooth electrode, this device showed a fourfold increase in the flow velocity at −0.9 V. The electrodes were also used as a valve. The ability to stop an intruding solution and the switching speed was improved with the micropillar structure.

Electrical-potential induced surface wettability of porous metallic nanostructures

“…Wettability was also affected by pore size, with larger pore sizes 25 exhibiting less wetting. Based on the Young−Lippmann model, a modified equation was 26 proposed to express the force balance between absorbing and repelling at the pore walls. The 27 force balance model was established in terms of the height of a water droplet in the pore.…”

Switchable imbibition in nanoporous gold

“…Imbibition under open-circuit conditions We started the imbibition experiment under open circuit conditions. Gold surfaces are hydrophilic when exposed in atmosphere, with a gold-water contact angle θ ∼ 70 • [39,40]. Therefore, once the electrolyte touches the NPG sample , it is spontaneously imbibed.…”

In situ digital microfluidic conductance sampling

“…Numerous phenomenological techniques exist for inducing fluid actuation, and techniques based on electroosmosis [7,8], electrowetting [9][10][11][12][13][14][15], dielectrophoresis [16][17][18], thermocapillary pumping [19,20], and photochemical actuation [21] have all been successfully demonstrated. The direct electrical actuation mechanisms listed here [7][8][9][10][11][12][13][14][15] are particularly intriguing since such processes can be implemented in digital architectures with underlying square electrode grids providing the digital actuation control structure.…”

“…The direct electrical actuation mechanisms listed here [7][8][9][10][11][12][13][14][15] are particularly intriguing since such processes can be implemented in digital architectures with underlying square electrode grids providing the digital actuation control structure. However, these single-layered techniques become increasingly challenging when implemented in complex two-dimensional digital systems.…”