Reversibly Light‐Switchable Wettability of Hybrid Organic/Inorganic Surfaces With Dual Micro‐/Nanoscale Roughness

Abstract

Here, an approach to realize “smart” solid substrates that can convert their wetting behavior between extreme states under selective light irradiation conditions is described. Hybrid organic/inorganic surfaces are engineered by exploiting photolithographically tailored SU‐8 polymer patterns as templates for accommodating closely packed arrays of colloidal anatase TiO2 nanorods, which are able to respond to UV light by reversibly changing their surface chemistry. The TiO2‐covered SU‐8 substrates are characterized by a dual micro‐/nanoscale roughness, arising from the overlapping of surfactant‐capped inorganic nanorods onto micrometer‐sized polymer pillars. Such combined architectural and chemical surface design enables the achievement of UV‐driven reversible transitions from a highly hydrophobic to a highly hydrophilic condition, with excursions in water contact angle values larger than 100°. The influence of the geometric and compositional parameters of the hybrid surfaces on their wettability behavior is examined and discussed within the frame of the available theoretical models.

Wettability of porous two‐dimensional ZnO nanocrystal films

“…Meanwhile, water and oxygen may compete to dissociatively absorb on these vacancies. The above enhance the surface hydrophilicity and the water contact angle is reduced (Feng et al, 2004;Caputo et al, 2008Caputo et al, , 2009a. The surface of ZnO crystals becomes energetically unstable after the hydroxyl adsorption and oxygen absorption on the defect sites is more strong than hydroxyl groups.…”

“…The contact angle reduction is generally observed in other ZnO structures under UV illumination (Feng et al, 2004). The origin of light-induced hydrophilicity has been explained on the base of creation of oxygen vacancies (Feng et al, 2004;Caputo et al, 2008Caputo et al, , 2009a. UV irradiation will generate electron-hole pairs in the ZnO surface and some holes can react with lattice oxygen to form surface oxygen vacancies.…”

“…Feng et al (2004 found that reversible super-hydrophobicity to super-hydrophilicity transition was observed and controlled by alternation of UV irradiation and dark storage on aligned ZnO nanorod films. Caputo et al reported that thin-film coatings of TiO 2 nanorods with surfactant could achieve UV light-driven conversion from hydrophobic to hydrophilic (Caputo et al, 2008(Caputo et al, , 2009a. The reversible conversion from hydrophobic to hydrophilic state is a new concept for smart engineered films.…”

“…Recently, the manipulation of the light-induced wettability changes of inorganic oxide (such as ZnO, TiO 2 ) films have been investigated (Feng et al, 2004;Caputo et al, 2008Caputo et al, , 2009aDas et al, 2009;Papsdopoulou et al, 2009). Feng et al (2004 found that reversible super-hydrophobicity to super-hydrophilicity transition was observed and controlled by alternation of UV irradiation and dark storage on aligned ZnO nanorod films.…”

Surface Morphology Analysis of Composite Thin Films based on Titanium-Dioxide Nanoparticles

“…The filler nanoparticles were nanocrystals of titania, which were prepared in our laboratory according to chemical synthesis previously described [19]. The primary nanocrystals had typical size of ≈ 30 nm length and ≈ 4 nm diameter.…”