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    Scalable Superomniphobic Surfaces

    Year: 2020

    Journal: J. Microelectromech. Syst., Volume 29, FEB, page 54–61

    Authors: Rontu, Ville; Jokinen, Ville; Franssila, Sami

    Organizations: Finnish Cultural FoundationFinnish Cultural Foundation; Academy of FinlandAcademy of FinlandEuropean Commission [297360]

    Keywords: Cassie Wenzel transition; microfluidics; plasma etching; self-cleaning; silicon; superhydrophobic; superoleophobic

    Superomniphobic surfaces that repel liquids of extremely low surface tension rely on carefully fabricated doubly re-entrant topographies, typically made by silicon deep reactive ion etching technology. However, previously published processes have depended on critically timed etching steps, which are difficult to downscale. We present a scalable process that eliminates the critically timed etching steps. It is based on the use of silicon-on-insulator wafers and a silicon oxide foot of the micropillar, which makes the isotropic silicon release step non-critical. The process allows easy downscaling of pillars from 20 $mu text{m}$ to 10 $mu text{m}$ and $5mu text{m}$ . The downscaling increases the stability of the Cassie state. Based on the process, we are able to create superomniphobic surfaces that sustain perfluorohexane (FC-72), which has the lowest surface tension of the known liquids at room temperature ( $gamma _{text {lv}}=11.91$ mN/m at 20 degrees C), in the Cassie state at droplet diameters down to 200 micrometers. These are the smallest perfluorohexane droplets repelled to date. [2019-0207]
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