Scalable Superomniphobic Surfaces

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 noncritical. The process allows easy downscaling of pillars from 20 μm to 10 μm and 5 μm. 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 (γlv = 11.91 mN/m at 20 °C), in the Cassie state at droplet diameters down to 200 micrometers. These are the smallest perfluorohexane droplets repelled to date.