Abstract
Controllable wettability is important for a wide range of applications, including intelligent switching, self-cleaning and oil/water separation. In this work, rapid switching and extreme wettability changes upon ultraviolet (UV) illumination were investigated. TiO2 nanoparticles were modified in solutions of trimethoxy(alkyl)silane, and the suspensions were sprayed on glass substrates. For such samples, the water contact angle (WCA) was shown to transition from a superhydrophobic (WCA ≈ 165°) to a superhydrophilic (WCA ≈ 0°) state within 10 min upon UV illumination and subsequent recovery to superhydrophobicity occurred after heat treatment. It was found that the changes in the trimethoxy(alkyl)silane upon UV illumination can explain the rapid decrease of the WCA from more than 165° to almost 0°. To further investigate the wettability transition, trimethoxy(alkyl)silane and Al2O3 nanoparticles (which are not photocatalytic) were mixed and spray-coated onto the glass substrates as the control samples. Then the unrecoverable change of trimethoxy(alkyl)silane under UV illumination can be confirmed. It was found that the presence of trimethoxy(alkyl)silane in the TiO2–trimethoxy(alkyl)silane coating served to speed up the super-wettability transition time from superhydrophobicity to superhydrophilicity, but also limited the number of wettability recycle times. With this understanding, the effect of the trimethoxy(alkyl)silane concentration on the number of recycle cycles was investigated.
Highlights
Wettability is an important property of solid surfaces governed by surface chemistry and surface topography [1,2] and has found significant applications in various fields [3,4,5,6,7,8]
The hydrophilic TiO2 nanoparticles were modified in ethanol solutions of PFOS, and the suspensions were sprayed on glass substrates to make the TiO2–PFOS samples
TiO2 nanoparticles modified with PFOS were applied on glass substrates to achieve fast, switchable super-wettability, demonstrated by a water contact angle (WCA) that could be recovered from ≈165° to almost 0°
Summary
Wettability is an important property of solid surfaces governed by surface chemistry and surface topography [1,2] and has found significant applications in various fields [3,4,5,6,7,8]. TiO2 nanoparticles modified with organic materials that have a low surface energy could be used to induce the property of switchable wettability under UV illumination. The wettability transition time from superhydrophobic (WCA ≈ 158°) to superhydrophilic (WCA ≈ 0°) occurred within 120 min of UV illumination.
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