Transparent, Superhydrophobic Surfaces from One-Step Spin Coating of Hydrophobic Nanoparticles

Superhydrophobic surface with a water contact angle of 150° or higher and very little flow resistance are of interest for numerous applications, including self-cleaning coatings, impermeable textiles, microfluidics, lab-on-a-chip devices, and biotechnology. To create superhydrophobic surface, a combination of low surface energy chemistry and dual-scaled (micro and nano) surface roughness is needed. There has been significant progress both theoretically and experimentally in creating topographically rough surfaces with extremely high water-repellency.

In this Study they present the nonwettability and transparency from the assembly of fluorosilane modified silica nanoparticles (F-SiO2 NPs) via onestep spin-coating and dip-coating without any surface postpassivation steps. When spin-coating the hydrophobic NPs (100 nm in diameter) at a concentration ≥0.8 wt % in a fluorinated solvent, the surface exhibited superhydrophobicity with an advancing water contact angle greater than 150° and a water droplet (5 μL) roll-off angle less than 5°. In comparison, superhydrophobicity was not achieved by dip-coating the same hydrophobic NPs. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) images revealed that NPs formed a nearly close-packed assembly in the superhydrophobic films, which effectively minimized the exposure of the underlying substrate while offering sufficiently trapped air pockets. In the dipcoated films, however, the surface coverage was rather random and incomplete. Therefore, the underlying substrate was exposed and water was able to impregnate between the NPs, leading to smaller water contact angle and larger water contact angle hysteresis. The spincoated superhydrophobic film was also highly transparent with greater than 95% transmittance in the visible region. Further, we demonstrated that the one-step coating strategy could be extended to different polymeric substrates, including poly(methyl methacrylate) and polyester fabrics, to achieve superhydrophobicity.

To sum up they reported a simple procedure to create a superhydrophobic surface by spin-coating fluorosilane-functionalized silica NPs without any post-treatment of the substrate with a low-surface-energy coating. The method is simple and versatile; superhydrophobicity is achieved on Si wafer, glass substrate, PMMA, and polyester fabric, however it needs to be improved.

Transparent, Superhydrophobic Surfaces from One-Step Spin Coating of Hydrophobic Nanoparticles

Lebo Xu, Raghuraman G. Karunakaran, Jia Guo, and Shu Yang*

Department of Materials Science and Engineering, University of Pennsylvania, 3231 Walnut Street, Philadelphia, Pennsylvania 19104, United States

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