Fabrication of Transparent and Microstructured Superhydrophobic Substrates Using Additive Manufacturing.

We report facile one- and two-step processes for the fabrication of transparent ultrahydrophobic surfaces and three-dimensional (3D)-printed superhydrophobic (SH) microstructures, respectively. In the one-step method, polydimethylsiloxane (PDMS) solution is treated thermally at 350 °C for 4 h, while PDMS-soot is generated and deposited on a glass slide to obtain a transparent SH surface without further chemical modification. For the two-step approach, SH surfaces are obtained by incorporating a 3D printing technique with a convenient hydrophobic coating method. Herein, we first 3D-print microstructured substrates with particular surface parameters, which are designed to facilitate a stable gas-trapping Cassie-Baxter (CB) wetting state based on a thermodynamic calculation. We subsequently coat the 3D-printed microstructures with candle soot (CS) or octadecyltrichlorosilane (OTS) solution to make superhydrophobic surfaces with mechanical durability. These surfaces exhibit an ultrahigh static water contact angle (CA, θ ≃ 158 ± 2 and 147 ± 2° for the CS and OTS coating, respectively) and a low roll-off angle for water droplets. Both static and dynamic (in terms of the advancing and receding) contact angles of a water droplet on the fabricated SH surfaces are in good agreement with the theoretical prediction of Cassie-Baxter contact angles. Furthermore, after a one-year-long shelf time, the SH substrates fabricated sustain good superhydrophobicity after ultrasonic water treatment and against several chemical droplets. All of these methods are simple, cost-effective, and highly efficient processes. The processes, design principle, and contact angle measurements presented here are useful for preparing transparent and superhydrophobic surfaces using additive manufacturing, which enables large-scale production and promisingly expands the application scope of utilizing self-cleaning superhydrophobic material.