An On‐Chip Liquid Metal Plug Generator

• Published in: Advanced materials (Weinheim) 2022-06, Vol.34 (23), p.e2201469-n/a
• Main Authors: Bhagwat, Sagar, O'Brien, Ciarán, Hamza, Ahmed, Sharma, Shatakshi, Rein, Christof, Sanjaya, Mario, Helmer, Dorothea, Kotz‐Helmer, Frederik, Pezeshkpour, Pegah, Rapp, Bastian E.
• Format: Article
• Language: English
• Subjects: 3D microprinting; Actuators; Aspect ratio; Casting; Constrictions; Electric potential; Electrochemical oxidation; Gallium; Liquid metals; Materials science; Microelectromechanical systems; Microfluidics; nonspherical droplets; Plugs; Polydimethylsiloxane; Reproducibility; Straight channels; Switches; Voltage
• ISSN: 0935-9648; 1521-4095
• DOI: 10.1002/adma.202201469

Gallium‐based liquid metal nonspherical droplets (plugs) have seen increasing demand recently mainly because their high aspect ratios make them beneficial for a wide range of applications, including microelectromechanical systems (MEMS), microfluidics, sensor technology, radio‐frequency devices, actuators, and switches. However, reproducibility of the generation of such plugs, as well as precise control over their size, is yet challenging. In this work, a simple on‐chip liquid metal plug generator using a commercially available 3D microprinter is presented and the plug generator in poly(dimethylsiloxane) is replicated via soft lithography. Liquid metal plugs are generated via a combination of electrochemical oxidation, design of well‐defined constrictions based on Laplace pressure, and the application of modulated voltage control signals. It is shown that plugs of various aspect ratios can be generated reproducibly for channel widths of 0.5, 0.8, and 1.5 mm with constriction widths of 0.1 mm at 6 V. Laplace‐pressure‐controlled plugs in constricted channels are compared to modulated‐voltage‐generated plugs in straight channels showing that this technique provides significantly enhanced reproducibility and control over the size and spacing between the plugs. This work paves the way to sub‐millimeter liquid metal plugs generated directly on‐chip for on‐demand MEMS and microfluidic applications. An on‐chip liquid metal plug generator is demonstrated. Reproducible liquid metal plugs of a given size are generated based on Laplace pressure tuning in constricted channels whereas plugs of varying sizes and interspacing are generated for modulated voltages in straight channels prefilled with 1 m NaOH. This device can be used to generate liquid metal plugs on demand directly on‐chip.