Abstract
Photo-induced super-hydrophilic thin films were fabricated on a quartz glass substrate by ultraviolet (UV) irradiation of a molecular precursor film at room temperature. A molecular precursor film exhibiting high solubility to both ethanol and water was obtained by spin-coating a solution involving a Ti(IV) complex; this complex was prepared by the reaction of Ti(IV) alkoxide with butylammonium hydrogen oxalate and hydrogen peroxide in ethanol. Transparent and well-adhered amorphous thin films of 160–170 nm thickness were obtained by weak UV irradiation (4 mW·cm−2 at 254 nm) of the precursor films for over 4 h at room temperature. The resultant thin films exhibiting low refractive indices of 1.78–1.79 were mechanically robust and water-insoluble. The chemical components of the thin films were examined by means of Fourier transform-infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS) spectra, focusing on the presence of the original ligands. The super-hydrophilic properties (evaluated based on the water contact angles on the surfaces) of the thin films after being kept in a dark condition overnight emerged when the aforementioned UV-light irradiation was performed for 10 min. It was additionally clarified that the super-hydrophilicity can be photo-induced repeatedly by UV irradiation for 10 min (indicated by a contact angle smaller than 4°) even after the hydrophilic level of the thin films had once been lowered by being in a dark condition for 4 h.
Highlights
A hydrophilic surface effectively imparts self-cleaning and anti-fogging properties to various products such as windows, mirrors, and walls
This present work demonstrates that the precursor film involving Ti(IV) complex could be converted to an unprecedented amorphous thin film by using a weak UV irradiation from an inexpensive germicidal lamp, at room temperature under a non-ozone environment
In this work applying UV irradiation to fabricate the thin films from a precursor involving a Ti(IV) complex salt, a stable amorphous thin film could be obtained by a short UV-irradiation time of 4 h, even at room temperature; the functionality of photo-induced super-hydrophilicity with contact angle smaller than 4◦ are achievable
Summary
A hydrophilic surface effectively imparts self-cleaning and anti-fogging properties to various products such as windows, mirrors, and walls. In order to impart these properties to material surfaces, numerous methods have been investigated involving surface coating by TiO2 [1,2,3,4], WO3 composite [5], and polydimethylsiloxane [6]. Nagai et al reported the fabrication of an O-deficient rutile thin film on a quartz glass substrate by heat treating a precursor film involving Ti(IV) complexes, by means of the molecular precursor method (MPM) [11]. We fabricated a photo-induced hydrophilic thin film through UV-irradiation of a molecular precursor film involving a Ti(IV) complex salt spin-coated on a quartz glass substrate. We report the fabrication and characterization of non-crystalline and transparent thin films exhibiting photo-induced super-hydrophilic property
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