Rapid, ultraviolet-induced, reversibly switchable wettability of superhydrophobic/superhydrophilic surfaces

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.

Smart Bionic Surfaces with Switchable Wettability and Applications

“…The inorganic semiconductor oxide materials with optical triggering-yielded electron-hole pairs usually are used to regulate the reversible light-responsive wettability, such as titanium dioxide (TiO 2 ), zinc oxide (ZnO), tin dioxide (SnO 2 ), tungsten trioxide (WO 3 ) and vanadium oxide (V 2 O 5 ) etc [29,55,56] . In the preparation of wettability-regulating superwettability surfaces, photosensitive inorganic semiconductor materials mainly utilize the free conversion of oxygen vacancies and hydroxyl groups under ultraviolet (UV) light irradiation and dark treatment (or heat treatment) to change the surface chemical polarity, thereby achieving the switchable wettability.…”

Titanium Dioxide Derived Materials with Superwettability

“…TiO 2 nanostructures have been grown on three-dimensional reduced graphene oxide porous structures and play an important role. Pan et al [71] reported a TiO 2 nanoparticle (NP) coating modified with 1H,1H,2H,2Hperfluorooctyl(trimethoxy)silane. The CAs could rapidly change from 165 • to 0 • in 10 min after heating.…”

Controllable Fabrication of Durable, Underliquid Superlyophobic Surfaces Based on the Lyophilic–Lyophobic Balance

“…Natural surfaces represented by the lotus leaf surface show superhydrophobic in air, and fish scales show superoleophobicity in water, having already disclosed an important role of the cooperation of surface chemical components and roughness on multiple scales. , Inspired by these marvelous natural materials, various surfaces with special superwettabilities have been developed. Most solid substrates exhibit irreversible wetting behaviors, for comparison, smart materials showing switchable superwetting properties are more desirable, as their surface wettability can be modulated by changing the surface chemistry via the employment of stimuli-responsive polymers, smart modifiers, and inorganic semiconductors − or by external stimuli including pH, light, temperature, and electricity. − …”