Fabrication of Transparent and Microstructured Superhydrophobic Substrates Using Additive Manufacturing

Abstract

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.

Aqueous construction of raspberry-like ZIF-8 hierarchical structures with enhanced superhydrophobic performance

“…In order to further explore the chemical heterogeneity and robustness of the prepared surface, the dynamic contact angles were evaluated by an extension/contraction method. [45][46][47] The results showed that the advancing and receding contact angles were 155.6°and 150.8°, respectively, with a hysteresis of 4.8°, which indicate that the surface has good hydrophobic uniformity.…”

Straightforward fabrication of robust and healable superhydrophobic steel mesh based on polydimethylsiloxane

“…Measurement of advancing contact angle ( θ A ), receding contact angle ( θ R ) and contact angle hysteresis were according to literatures 31–33 . Specifically, a 5 μL water droplet was first placed on the sample to achieve a stable equilibrium state.…”

“…Measurement of advancing contact angle (θ A ), receding contact angle (θ R ) and contact angle hysteresis were according to literatures. [31][32][33] Specifically, a 5 μL water droplet was first placed on the sample to achieve a stable equilibrium state. Then 3 μL water was injected in which an increase in the volume and subsequently in the base diameter of the droplet was observed.…”

Dynamic Wetting of Ionic Liquid Drops on Hydrophobic Microstructures

“…To theoretically predict the stable wetting states for water and ionic liquids on the studied surface, we used a model based on the comparison between the surface energies for a CB and a Wenzel drop on hydrophobic microstructures. The total surface energy for a CB or a Wenzel drop on the hydrophobic microtextures, denoted by E CB and E W , respectively, can be expressed by ,,, .25ex2ex E CB = S normalb false[ γ SG r + γ LG ( 1 − ϕ false( 1 + 0.25em cos nobreak0em.25em⁡ θ normalY false) false) ] + γ LG S cap E normalW = S normalb [ γ SG r − γ LG r cos ⁡ θ Y ] + γ LG S cap where S b is the drop’s base surface area, γ SG and γ LG are the solid–gas and liquid–gas interfacial tensions, respectively, r is the surface roughness, ϕ is the packing fraction, and S cap is the spherical cap surface area of the water drop completely in contact with the surrounding air.…”

“…The difference between the CB and Wenzel energies, Δ E = E CB – E W , enables us to predict the critical contact angle θ* when equating the two energies E CB = E W . Using the above equations, one can arrive at the physical criterion of the critical contact angle θ* that delineates the surface parameters for a stable CB vs Wenzel state, by equating E CB = E W ,,, 0.25em cos nobreak0em.25em⁡ θ * = ϕ − 1 r − ϕ This model suggests that a CB droplet is thermodynamically more stable when E CB < E W , which corresponds to a larger contact angle, θ > θ*. In addition, a stable Wenzel occurs when E W has lower energy compared to that of a CB wetting mode, that is, E W < E CB , by tuning the surface parameters of r and ϕ .…”