Surfactant-mediated electro-dewetting of droplets in oil for liquid-shape manipulation

Abstract

The capability to manipulate liquid shape at the microscale has enabled numerous microfluidic devices. Due to its simple electric actuation, electrowetting-on-dielectric has been widely used in a variety of microfluidic applications that require reversible liquid-shape modulation. However, its use of dielectric and hydrophobic layers raised operation voltage, caused reliability issues, and increased fabrication cost. As an alternative mechanism, ionic-surfactant-mediated electro-dewetting has recently been demonstrated to enable digital microfluidics in air with a much lower voltage, higher reliability, and simpler chip fabrication. However, electro-dewetting for liquid-shape manipulation has remained poorly explored due to its limited contact-angle changes. Here, we investigated electro-dewetting in oil by testing various droplet liquids and hydrophilic substrate materials. To guide device development, cationic surfactants with varying hydrocarbon chain lengths and concentrations are tested. A contact-angle change of 100° is obtained for electro-dewetting of a dimethyl sulfoxide droplet in hexadecane with mere 4 V. To evaluate the utility of electro-dewetting in oil, proof-of-concept devices are assembled to explore the potential in optical applications such as reflective displays and liquid lenses. Compatible with various liquids and substrates, electro-dewetting with the liquid-in-oil configuration opens a door for simpler and more reliable microfluidic devices.

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2025 The Author(s). Droplet published by Jilin University and John Wiley & Sons Australia, Ltd.