Reversible Photocontrol of Wood-Surface Wettability Between Superhydrophilicity and Superhydrophobicity Based on a TiO2 Film

The reversible photocontrol of wood-surface wettability between superhydrophilicity and superhydrophobicity based on a TiO₂ film modified with octadecyl trichlorosilane (OTS) was achieved via a facile hydrothermal method at low temperature. Under UV illumination, the wood surface became superhydrophilic with a water contact angle (WCA) of approximately 0°. However, when placed in the dark, a superhydrophobic wood surface with a WCA of approximately 152° was achieved. The mechanism of the reversible photocontrol of wood-surface wettability is discussed in this article. This photocontrolled wood surface may have potential for wood self-cleaning or manipulation in response to indoor humidity.     

Facile micro-patterning of ferromagnetic CoFe2O4 films using a combined approach of sol–gel method and UV irradiation

CoFe₂O₄ photosensitive sol was prepared using iron nitrate and cobalt nitrate as precursors, acetyl acetone as a chelating agent, and ethanol as a solvent. CoFe₂O₄ photosensitive sol was used to fabricate smooth and micro-patterned CoFe₂O₄ films. The effects of UV irradiation on the crystallinity, surface morphology and ferromagnetic properties of CoFe₂O₄ films were investigated. For the film prepared using conventional sol-gel process, the crystallization of spinel CoFe₂O₄ phase was completely finished at ~ 600?℃, and no intermediate phase was formed. However, when the sol-gel process was combined with UV irradiation, Fe₂O₃ and CoO intermediate phases were firstly generated, and then reacted to form CoFe₂O₄ phase. Facile micro-patterning of CoFe₂O₄ films can be realized using a combined approach of sol-gel method and UV irradiation without using any photoresist. The structure and functional properties of the CoFe₂O₄ film have not been affected during the patterning process, and its magnetic properties have also not been changed.     

Superhydrophilic Transparent Titania Films by Supersonic Aerosol Deposition

Photocatalytic and hydrophilic TiO₂ thin‐film applications include water purification, cancer therapy, solar energy conversion, self‐cleaning devices, and antifogging windows. We demonstrate superhydrophilicity of aerosol‐deposition (AD) TiO₂ films on a glass substrate without use of a carrier solvent, thereby removing the possibility of impurity contamination. AD films exhibit high visible light transmittance (greater than 80%) and superhydrophilicity (0° contact angle) with even minimal UV‐light irradiation exposure. This AD method represents a significant step toward the realization of economically viable, functional thin films for the aforementioned applications.     

Fast photo-switched wettability and color of surfaces coated with polymer brushes containing spiropyran

An intelligent photo-responsive spiropyran (SP)-contained surface that combines reversible wettability conversion with photochromic behavior was prepared on etched silicon substrates by atom transfer radical polymerization. The heterocyclic ring cleavage of SP moieties under UV irradiation leads to the change of the surface wettability and color. Water contact angle (CA) of the prepared surfaces change from 138.8° ± 1.3° to 42.7° ± 1.7° after 5 min under 365 nm UV irradiation and recover to its original state after 20 min of visible light irradiation, accompanied by the color change between yellowish and purple. To our knowledge, this result is the highest and fastest CA variation reported for surfaces containing SPs. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Effects of atomic oxygen and ultraviolet in low earth orbit on low surface energy polymer film

Effects of atomic oxygen (AO) and ultraviolet (UV) on a polymer film with surface energy of 8.0 mJ m⁻² derived from poly(1H,1H‐perfluorooctyl methylacrylate) were investigated by contact angle measurements, X‐ray photoelectron spectroscopy, and atomic force microscope. The film was exposed to AO with a flux of 6.73 × 10¹⁵ atoms cm⁻² s⁻¹ and UV with intensity of 15.8 mW cm⁻² at wavelength of 200–450 nm, respectively. It is found that AO and UV irradiation resulted in the reduction of film thickness, change of wettability, and increase of surface energy, and AO exhibited more serious effects than UV on the fluorinated polymer film. Reduced rate of thickness of the film was almost proportional to the AO exposure time. After exposed to AO and UV irradiation, the surface energy of the film increased to 17.3 mJ m⁻² and 11.0 mJ m⁻², respectively. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Reversibly light-switchable wettability between superhydrophobicity and superhydrophilicity of hybrid ZnO/bamboo surfaces via alternation of UV irradiation and dark storage

Functional bamboo surfaces with reversibly tunable wettability have become much sought after because of their usefulness in sustainable material protection strategies and industrial applications. In this paper, the hybrid ZnO/bamboo surfaces with reversibly light-switchable wettability between superhydrophobicity and superhydrophilicity were successfully prepared via a hydrothermal method at low temperature. The bamboo substrates served as adhesion, and the well-aligned ZnO nanosheet arrays (WZNA) were deposited on the bamboo surfaces after a hydrothermal process. A subsequent chemical treatment with octadecyltrichlorosilane (OTS) led to a superhydrophobic surface with a water contact angle (WCA) up to 153°. Under UV irradiation, the WCA decreased gradually, and the surface eventually became superhydrophilic because of hydroxyl absorption on the ZnO surfaces. The wetting behavior of the WZNA can be reversibly switched between superhydrophilic and superhydrophobic via alternation of UV exposure for 12 h and dark storage for 10 days.     

Photocatalytic water splitting over ZrO2 prepared by precipitation method

ZrO₂ prepared by the precipitation method of zirconium oxychloride with various hydrolyzing agents was studied for photocatalytic water splitting reaction under UV light irradiation. The crystal structure as well surface properties were varied with the hydrolyzing agent of KOH, NH₄OH, and NH₂CONH₂. Especially, the surface area of the prepared ZrO₂ calcined at the same temperature of 750 °C for 6 h was dependent highly on the hydrolyzing agent, and thus the highest photocatalytic activity was obtained for ZrO₂ with the highest surface area when KOH was used as a hydrolyzing agent, In the presence of Na₂CO₃, the photocatalytic activity of ZrO₂ increased by 2–3 fold, which was ascribed to the physically adsorbed carbonate species on the ZrO₂ surface. This paper is dedicated to Professor Hyun-Ku Rhee on the occasion of his retirement from Seoul National University.     

Fabrication of fluorocarbon terminated DLC thin film using soft X-ray

The control of wettability on a diamond-like carbon (DLC) thin film was carried out by exposing the film to synchrotron radiation (SR) ranging 50–1000 e V under perfluorohexane (C₆F₁₄) gas atmosphere. The contact angle of the DLC surface with a water droplet was found to increase from 73° to 114° by the SR irradiation under C₆F₁₄ gas atmosphere. The chemical components variations of the DLC surface were studied using X-ray photoelectron spectroscopy and the modified DLC film with F was studied using near-edge X-ray absorption fine structure spectroscopy. By mounting the new sample holder for the parallel SR irradiation, we succeeded in preventing secondary reaction of deposited material and controlling the contact angle of the fluorocarbon modified DLC surface.     

Superhydrophobic to superhydrophilic wettability transition of functionalized SiO2 nanoparticles

The superhydrophobic and superhydrophilic surfaces and their transitions are of great interest for the production of self-cleaning, anti-biofouling, or corrosion-resistant materials. This work reports the wettability transition from superhydrophobic to superhydrophilic SiO₂ nanoparticles functionalized with 1H, 1H, 2H, 2H-perfluorooctyltriethoxysilane (POTS) and induced by temperature. The functionalization of these nanoparticles was confirmed by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy. The functionalization of SiO₂ nanoparticles with POTS resulted in superhydrophobic surfaces with water contact angles up to 157°. A sudden transition to superhydrophilic behavior with water contact angles (WCA) below 5° was observed when the sample was heat-treated at 500 °C, despite the presence of fluorine on the surface of these nanoparticles, as confirmed by XPS and transmission electron microscopy. XPS suggested that the transition was caused by the change in orientation of the fluoroalkyl molecules and its partial decomposition due to the loss of the –CF₃ group, resulting in shorter chains with a tail-end group with C–O bonds, which promoted the superhydrophilicity.     

Rapid and facile low-temperature solution production of ZrO2 films as high-k dielectrics for flexible low-voltage thin-film transistors

A rapid lightwave (LW) irradiation method was presented for the low-temperature solution production of ZrO₂ films as high-k dielectrics for flexible high-performance thin-film transistors (TFTs). The LW irradiation process markedly decreased the required processing temperature and processing time. Microstructure characterizations confirmed the successful formation of ZrO₂ films with an ultrasmooth surface, large band gap (>5 eV) and low defect level. The ZrO₂ film produced via LW irradiation at ∼200 °C in only 8 min presented excellent dielectric properties, including a small leakage current of 3.3 × 10⁻⁸ A/cm² and a large capacitance of 296 nF/cm², significantly outperforming the films by the conventional high-temperature annealing process at 400 °C for 60 min. Furthermore, LW irradiation was extended to the channel layer. The rapid low-temperature solution-processed InZrO_x TFTs exhibited superior electrical characteristics, such as a high carrier mobility of 41.3 cm²V⁻¹s⁻¹ and a high on-off current ratio of 10⁵∼10⁶ at a low operation voltage of 3 V due to the employment of high-quality ZrO₂ dielectric films. Moreover, the flexible TFT on a polyimide (PI) plastic substrate achieved a high mobility of nearly 30 cm²V⁻¹s⁻¹, indicating that LW irradiation is highly promising for the rapid and low-temperature solution production of high-quality and flexible oxide electronic devices.     

Properties of solution-processed MgInZnO semiconductor thin films and photodetectors fabricated at a low temperature using UV-assisted thermal annealing

Ultraviolet (UV) irradiation-assisted thermal annealing is used for the fabrication of Mg doped InZnO (MIZO) semiconductor thin films and metal-semiconductor-metal (MSM) type photodetectors on alkali-free glasses at a low temperature of 300 °C. In this study, the effects of UV irradiation time on the structural features and the optical and electrical properties of sol-gel derived MIZO thin films were investigated, and the photoresponse properties of MIZO photodetectors fabricated using UV-assisted thermal annealing (UV-TA) and conventional thermal annealing (CTA) were compared. The molar ratio of In:Zn was fixed at 3:2, and the Mg content was maintained at 20 at% ([Mg]/[In+Zn]) in the precursor solution. After a spin-coating and drying procedure was performed twice, the dried sol-gel films were heated on a hotplate at 300 °C and exposed to UV irradiation in ambient air. The UV irradiation time was adjusted to 1, 2, 3, and 4 h. All annealed MIZO thin films had a dense microstructure, uniform film thickness, and flat surface and exhibited good optical transmittance (> 86.0%). The mean resistivity decreased with increasing irradiation time, and the samples irradiated for 4 h exhibited the lowest mean resistivity of 4.4×10² Ω-cm. Current-voltage (I-V) characteristics showed that the MIZO photodetectors operated in the photoconductive mode. Under illumination with UVC light, the MIZO photodetectors exhibited an I_light-to-I_dark ratio of 7.7 × 10² and had a photoresponsivity of 5.0 A/W at a bias of 5 V.     

In situ DRIFTS study of photocatalytic CO<Subscript>2</Subscript> reduction under UV irradiation

Photocatalytic reduction of CO₂ on TiO₂ and Cu/TiO₂ photocatalysts was studied by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) under UV irradiation. The photocatalysts were prepared by sol-gel method via controlled hydrolysis of titanium (IV) butoxide. Copper precursor was loaded onto TiO₂ during sol-gel procedure. A large amount of adsorbed H₂O and surface OH groups was detected at 25°C on the TiO₂ photocatalyst after being treated at 500°C under air stream. Carbonate and bicarbonate were formed rapidly due to the reaction of CO₂ with oxygen-vacancy and OH groups, respectively, on TiO₂ surface upon CO₂ adsorption. The IR spectra indicated that, under UV irradiation, gas-phase CO₂ further combined with oxygen-vacancy and OH groups to produce more carbonate or bicarbonate. The weak signals of reaction intermediates were found on the IR spectra, which were due to the slow photocatalytic CO₂ reduction on photocatalysts. Photogenerated electrons merge with H⁺ ions to form H atoms, which progressively reduce CO₂ to form formic acid, dioxymethylene, formaldehyde and methoxy as observed in the IR spectra. The well-dispersed Cu, acting as the active site significantly increases the amount of formaldehyde and dioxymethylene, thus promotes the photoactivity of CO₂ reduction on Cu/TiO₂. A possible mechanism of the photocatalytic CO₂ reduction is proposed based on these intermediates and products on the photocatalysts.     

In situ DRIFTS study of photocatalytic CO2 reduction under UV irradiation

Photocatalytic reduction of CO₂ on TiO₂ and Cu/TiO₂ photocatalysts was studied by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) under UV irradiation. The photocatalysts were prepared by sol-gel method via controlled hydrolysis of titanium (IV) butoxide. Copper precursor was loaded onto TiO₂ during sol-gel procedure. A large amount of adsorbed H₂O and surface OH groups was detected at 25°C on the TiO₂ photocatalyst after being treated at 500°C under air stream. Carbonate and bicarbonate were formed rapidly due to the reaction of CO₂ with oxygen-vacancy and OH groups, respectively, on TiO₂ surface upon CO₂ adsorption. The IR spectra indicated that, under UV irradiation, gas-phase CO₂ further combined with oxygen-vacancy and OH groups to produce more carbonate or bicarbonate. The weak signals of reaction intermediates were found on the IR spectra, which were due to the slow photocatalytic CO₂ reduction on photocatalysts. Photogenerated electrons merge with H⁺ ions to form H atoms, which progressively reduce CO₂ to form formic acid, dioxymethylene, formaldehyde and methoxy as observed in the IR spectra. The well-dispersed Cu, acting as the active site significantly increases the amount of formaldehyde and dioxymethylene, thus promotes the photoactivity of CO₂ reduction on Cu/TiO₂. A possible mechanism of the photocatalytic CO₂ reduction is proposed based on these intermediates and products on the photocatalysts.     

Quality optimization of Bi2212 films prepared by aqueous solvent sol-gel method with nonionic surfactants

In this paper, Bi2212 films were prepared on LaAlO₃(100) and SrTiO₃(100) substrates by the sol-gel method using Bi(NO₃)₃·5H₂O, Sr(NO₃)₂, Ca(NO₃)₂·4H₂O and Cu(NO₃)₂·3H₂O as raw materials. TritonX-100 (TX-100), fatty alcohol poly oxyethylene ether (AEO-9), poly (vinylpyrrolidone) (PVP) and poly (vinyl alcohol) (PVA) were used as surfactants, respectively, to improve the wettability between the sol and the substrate. When glycine and glycolic acid were used as complexing agents, these surfactants were stably miscible with the sols. The effects of different surfactant sol-gel systems on the wettability of substrates as well as the crystallinity, morphology, surface roughness and electrical transport properties of Bi2212 superconducting films were investigated. The results showed that flat and continuous c-axis epitaxial Bi2212 films were obtained using all these sol-gel systems. In particular, TX-100 and AEO-9 as surfactants showed stronger wettability of the sol-gel for both substrates. In addition, the films prepared using polymer surfactants PVP and PVA sol-gel systems showed less surface roughness. The same patterns were found in all the film samples prepared using precursor sols of different complexing agents, and all the films exhibited good electrical transport properties. This work lays a certain research foundation for the preparation of thin films by aqueous solvent sol-gel method. The method also shows great potential in terms of the stability of different sol-gel systems and the improvement of the wettability of different substrates.     

Effect of sputtering parameters on the self-cleaning properties of amorphous titanium dioxide thin films

The aim of this work was to assess the effect of the direct current magnetron sputtering parameters on the photocatalytic activity and photoinduced wettability of amorphous TiO₂ films. TiO₂ films were deposited on glass using the direct current magnetron sputtering technique, without heating, at different total working pressures. Qualitative analysis using in situ X-ray photoelectron spectroscopy confirmed the TiO₂ stoichiometry of the deposited films. Surface structure was studied as a function of working pressure using scanning electron microscopy. The hydrophilicity of the TiO₂ surfaces was investigated macroscopically using measurements of the water contact angle. A threshold working pressure was observed, with a strong dependence on the film thickness. A super hydrophilic surface was observed after less than 1 h of UV irradiation. The photocatalytic activity of the films was evaluated under UV light through the degradation of methylene blue (\(\lambda_{\hbox{max} } \approx 660\;{\text{nm}}\)). The effect of UV irradiation on the photocatalytic activity was rapid, strong, and dependent on film thickness and total working pressure. Fifty percent of organic compounds were photodegraded by films with a thickness of 60 nm deposited at 10 mTorr.     

Interfacial microstructure and strengthening mechanisms of Cf/Mg composite with double-layer interface

In order to overcome the interfacial incompatibility of carbon fiber reinforced magnesium matrix (C_f/Mg) composites, a double-layer interface (ZrO₂–MgO) is designed in this work. Carbon fiber was modified with ZrO₂ coating by sol-gel process. Microstructural examination reveals that MgO layer forms on the surface of ZrO₂ coating by ZrO₂ reacting with Mg during the composite fabrication. Such double-layer interface could inhibit Al₄C₃ and hence prevent fiber damage. Meanwhile, the wettability was improved for the reaction between ZrO₂ and Mg. Thus the tensile strength of ZrO₂-C_f/AZ91D composite was 68.0% higher than that of the unmodified one. Due to the fiber bundle pull-out, debonding and crack deflection, the toughness of C_f/Mg composite with double-layer interface is increased simultaneously.     

Novel synthesis of ZrO2-SiCw-C insert ring materials for slide plates

To reduce the cost and firing temperature of traditional ZrO₂ insert rings, the new ZrO₂-SiC_w-C (w-whisker) insert ring materials were successfully synthesized using ZrO₂, Si, graphite powders as starting materials, and phenolic resin as binder. The effects of amount of Si powder addition (5, 8 and 11 wt%) and firing temperatures (1100 °C, 1200 °C and 1400 °C) on the phase composition, microstructure and properties of as-obtained products have been investigated. The results show that Si reacts with C or CO at high temperature to form SiC_w, which intersperses in the ZrO₂ material to develop an interlocking network structure, resulting in strengthening effect and leading to an increase in the strength of the composites. The composites have good oxidation resistance due to the formation of some glass film on the sample surface. The optimum firing temperature is 1200 °C, which is much lower than that of pure ZrO₂ material (>1700 °C). The as-prepared ZrO₂-SiC_w-C materials possess good properties, making good prospects for fabricating insert rings of slide plates.     

Properties of t-zirconia prepared by a composite-assisted nonhydrolytic sol-gel

High surface area and highly crystalline tetragonal Ni-Si-doped ZrO₂ samples were prepared using a nonhydrolytic sol-gel method. The synthesis involved the condensation of zirconium chloride and isopropyl ether in the presence of a chitosan-based composites containing Ni and Si (Ni@Si-CS), followed by calcination to remove the CS. The interactions between the zirconium precursor and the Ni@Si-CS composites were studied and correlated with the effect on morphologies, crystalline structure, phase compositions, and surface area. These parameters were evaluated for different Ni@Si-CS to ZrO₂ mass ratios. It was found that increasing the concentration of Ni@Si-CS composite led to smaller grains of ZrO₂ nanocrystals and an overall material with a higher surface area. The stability of the tetragonal/cubic phases following calcination at 800°C was correlated with the presence of low amounts of Ni²⁺ in the sublattice of ZrO₂ and the presence of the Si-chitosan, which acted as steric stabilizer.     

Preparation of super-hydrophilic amorphous titanium dioxide thin film via PECVD process and its application to dehumidifying heat exchangers

The super-hydrophilic amorphous titanium dioxide (TiO₂) thin film was prepared by plasma-enhanced chemical vapor deposition (PECVD) process for an application to dehumidifying finned-tube heat exchangers. The chemical components and surface structure were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and scanning electron microscope (SEM). The wettability and long-term durability were investigated by measuring the water contact angle and by performing wet/dry cycles. The samples were subjected to 1000 times of wet/dry cycles to establish long-term durability. The water contact angle of the amorphous TiO₂ thin film was about 8° at as-deposited film with O₂ plasma treatment and was about 15° after 1000 wet/dry cycles. The amorphous TiO₂ thin film had excellent wettability and long-term durability under full wetting conditions.     

The effect of side chains on the reactive rate and surface wettability of pentablock copolymers by ATRP

The reactive rate and surface wettability of three pentablock copolymers PDMS‐b‐(PMMA‐b‐PR)₂ (R = 3FMA, 12FMA, and MPS) obtained via ATRP for coatings are discussed. Poly(dimethylsiloxane) (PDMS) is used as difunctional macroinitiator, poly(methyl methacrylate) (PMMA) as the middle block, while poly(trifluoroethyl methacrylate) (P3FMA), poly(dodecafluoroheptyl methacrylate) (P12FMA) and poly(3‐(trimethoxysilyl)propyl methacrylate) (PMPS) as the end block, respectively. Their reactive rates obtained by gas chromatography (GC) analysis indicate that 3FMA gains 8.053 × 10^?5 s^?1 reactive rate and 75% conversion, higher than 12FMA (4.417 × 10^?5 s^?1, 35%), but MPS has 1.9389 × 10^?4 s^?1 reactive rate and 96% conversion. The wettability of pentablock copolymer films is characterized by water contact angles (WCA) and hexadecane contact angles (HCA). The PDMS‐b‐(PMMA‐b‐P12FMA)₂ film behaves much higher advancing and receding WAC (120° and 116°) and HCA (60° and 56°) than PDMS‐b‐(PMMA‐b‐P3FMA)₂ film (110° and 106° for WAC, 38° and 32° for HAC) because of its fluorine‐rich surface (20.9 wt % F). However, PDMS‐b‐(PMMA‐b‐PMPS)₂ film obtains 8° hysteretic contact angle in WAC (114°–106°) and HAC (32°–24°) due to its higher surface roughness (138 nm). Therefore, the fluorine‐rich and higher roughness surface could produce the lower water and oil wettability, but silicon‐rich surface will produce lower water wettability. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40209.