Excellent Self-cleaning Properties Research Articles

Study on dynamics and freezing behaviors of water droplet on superhydrophobic aluminum surface

In this work, a kind of superhydrophobic aluminum surface (treated-Al-SA) is fabricated by chemical etching using hydrochloric acid and hydrogen peroxide, and then treated by stearic acid. The surface of treated-Al-SA has typical hierarchical structure, which hold its durable superhydrophobicity under water droplet impact test, bending test, temperature test, humidity test and corrosive liquids test. Moreover, treated-Al-SA show excellent self-cleaning property at the different tilt angle under room temperature. Results on the dynamic behavior of water droplet is indicated the good anti-adhesion and superhydrophobicity of the treated-Al-SA. The whole freezing process of the water droplets on the surface of untreated-Al and treated-Al-SA is observed. The freezing time of treated-Al-SA is 59 s, which is longer than that of untreated-Al. It is estimated that the different anti-freezing behavior is caused by the thermal conductivity between the water droplet and plate, which is provided an insight into freezing characteristics of water droplet. This study is offered the novel opinion of the superhydrophobic aluminum surface produced by chemical etching, which may help the application of structured aluminum surface.

Self - Cleaning Property of Ag/TiO<sub>2</sub> Thin Film

Ag/TiO2 thin film was prepared by the sol-gel method through the hydrolysis of titanium tetraisopropoxide and silver nitrate solution. Spin coating method was used to get uniform film on ITO glass substrate followed by annealing process for 1 hour. After that, all the samples were characterised using GIXRD and FESEM and undergone water contact angle test and MB degradation. Silver ion concentrations were varied to observe the effect on crystalline state, morphology, wettability and photocatalytic properties. The results showed that Ag/TiO2 thin film was in anatase phase and it could degrade nearly 70% of methylene blue after 150 min illumination. The formed Ag/TiO2 thin film has excellent self-cleaning property with compact, continuous, smooth, and good hydrophilicity property.

Robust superhydrophobic surface fabrication by fluorine-free method on filter paper for oil/water separation

Robust superhydrophobic surface exhibiting anti-fouling and self-cleaning ability were successfully fabricated by nano TiO2 modified by γ-aminopropyltriethoxysilane (KH550) and polydimethylsiloxane (PDMS) via wire rod coating. Due to the lower surface energy of PDMS and the hierarchical structure caused by the different aggregation sizes of TiO2 nanoparticles, the contact angle of the resulting superhydrophobic coating was 154.5° and the rolling angle was 3.5°. And the coated paper still had good non-wettability under water immersion. In addition, the coated paper was tolerant to mechanical damage and various temperature conditions. Even after 40 sandpaper wear cycles, the coating can still maintain good mechanical stability and superhydrophobicity. The superhydrophobic paper was used for oil-water separation, the separation efficiency was about 98% even after used 10 times. Furthermore, the prepared superhydrophobic paper exhibited excellent self-cleaning and anti-fouling properties, as well as demonstrated superb resistance to various water solutions owing to its high hydrophobicity. Moreover, the prepared superhydrophobic paper has application prospects in the industry of special wetting materials.

A Coral Reef-like Structure Fabricated on Cellulose Paper for Simultaneous Oil-Water Separation and Electromagnetic Shielding Protection.

The functional design of paper-based material surfaces with renewable functions and environmentally friendly properties is prevalent nowadays. Herein, a superhydrophobic surface with a coral reef-like structure was prepared on filter paper by electroless copper plating, rapid silver nitrate etching, and facile 1-hexadecanethiol impregnation. After low-surface-energy thiol treatment, this unique coral reef-like structure surface showed excellent superhydrophobicity with a water contact angle of 163.8° and superoleophobicity with an oil contact angle of 0°, which could be used for oil–water separation and had a separation efficiency above 89.17% after 12 consecutive oil–water separations. Because the copper layer and silver nanostructure are both excellent conductive materials, the modified paper exhibited excellent electromagnetic shielding properties, and the electromagnetic interface shielding effectiveness exceeded 63 dB from 9 kHz to 1.5 GHz. The modified paper also had excellent self-cleaning properties and a better corrosion resistance. The unique three-dimensional interweaving structure between the cellulose fibers in the filter paper is fully utilized, and the substitution reaction between the silver ion and the copper coating produces a coral reef-like structure, which provides a new strategy for promoting the wide application of paper-based materials.

Preparation of superhydrophobic surface with tunable adhesion on glass substrate

Superhydrophobic coatings help to reduce the surface contamination of glass and improve its performance. A SiO2 nanoparticles superhydrophobic surface with tunable adhesion is obtained on a glass substrate after modifying with PDMS. With the water contact angle of 155.1 ± 3°, the superhydrophobic surface also shows excellent self-cleaning property, good durability and thermal stability. This method is facile, cost-effective and easy to operate and will expand the potential applications of glass materials in different fields.

Engineering a superwettable polyolefin membrane for highly efficient oil/water separation with excellent self-cleaning and photo-catalysis degradation property

Membrane technology has been intensively applied to the treatment of oily wastewater in recent years. Extensive progress has been made to design super-wetting membranes for separating stratified or emulsified oil/water mixtures. However, the membrane with small pore size is ineffective due to the severe decline of permeation, while the membrane with large pore size exhibits a poor separation efficiency for emulsion separation. Accordingly, a promising separation mechanism has been developed to improve the separation efficiency of the membrane with large pore size relying on the joint effect of demulsification and coalesce. Inspired by this strategy, a negatively charged superhydrophilic membrane is fabricated via the deposition of β-FeOOH nanorods on the commercialized sulfonated polyolefin lithium-ion battery separators (LIBS). The abundant sulfo groups on the polyolefin surface offer enough binding sites to anchor β-FeOOH nanorods. The fabricated membrane is qualified for separating stratified and emulsified oil/water mixtures, predominantly facilitated by the superwettability (underwater oil contact angle of 154° and underwater oil rolling angle of 3°) and the demulsification effect. A comprehensive oil/water separation performance of the composite membrane for the stratified and highly emulsified surfactant-free and surfactant-emulsified oil/water mixtures is obtained, with the respective permeation flux of up to 55503, 4112 and 1260 L m-2 h-1 and the corresponding separation efficiency of 99.9%, 99.2% and 98.7% solely driven by gravity. Moreover, considering the photo-Fenton catalysis of β-FeOOH, the hybrid membrane exhibits an excellent self-cleaning property, good nanorods coating stability and superior dye degradation ability. More importantly, LIBS possess some unique advantages of commercial availability, chemical tolerance, good flexibility and excellent mechanical strength, which provides an attempt to explore a novel high-efficiency oil/water separation material.

Superhydrophobic silicone rubber surface prepared by direct replication

ABSTRACT The superhydrophobic surface of silicone rubber was prepared by means of a simple direct replication and compression moulding process. It was worth noting that the rough structure endowed the surface of the silicone rubber with excellent superhydrophobic, low adhesion and self-cleaning properties. The contact angle with water was 158.5 ± 0.5°, and the rolling angle was 8.9 ± 0.1°. Even if immersed in water, the surface will not become wetted by the water. In addition, it has excellent properties of hydrophobic hydrochloric acid solution, sodium hydroxide solution and sodium chloride solution. Through a high-speed camera, it was found that water droplets would bounce up after falling on the superhydrophobic surface of the silicone rubber. When the liquid drops fall perpendicular to the superhydrophobic surface of silicone rubber, the time of contact between the liquid drops and the superhydrophobic surface is not inversely proportional to the height of the drop falling.

Fabrication of Superhydrophobic Film on the Surface of Indonesian Bamboo Timber by TiO<sub>2</sub> Deposition and Using Octadecyltrichlorosilane as a Surface Modifier Agent

The tropical bamboo has been widely used in modern society as a potential material for various applications. It is well known that bamboo has low durability due to its hydrophilic properties. To overcome this problem, the superhydrophobic surface on Indonesian bamboo timber had been successfully fabricated via hydrothermal deposition of an anatase TiO2 and solution immersion of octadecyltrichlorosilane (ODTS), which exhibited a maximum water contact angle (WCA) of 155°. The as-fabricated superhydrophobic bamboo timber not only showed high mechanical resistance against the abrasion of SiC sandpaper but had also been proven to possess high chemical stability after immersion in acidic and basic aqueous solutions. Moreover, the superhydrophobic bamboo timber also demonstrated excellent self-cleaning and flame-resistance properties, in comparison to pure bamboo timber. It is believed that the strategy offered in this study can increase the utilization of bamboo timber for various purposes, especially as a self-cleaning material.

Tuning of hydrophobicity of WO3-based hot-dip zinc coating with improved self-cleaning and anti-corrosion properties

Hot-dip galvanic (ZnAl) coatings with enhanced self-cleaning and anti-corrosion attributes were developed through effective incorporation of WO3 nanoparticles. The wet-synthesized WO3 nanoparticles were systematically characterized for crystallinity, optical properties, bonding characteristics, compositional purity, chemical state, morphology, size distribution, and colloidal and thermal stability; and successfully assimilated into the galvanic coating. High water contact angles (112.3°) recorded for the composite coating revealed improved hydrophobicity of the tuned surface. The coating displayed excellent self-cleaning property against the applied dirt particles. The hydrophobic WO3 nanoparticles-incorporated coating exhibited superior anti-corrosion performance than the conventional bare ZnAl coating as revealed by scanning Kelvin probe microscopic studies, long-term potential measurements, Tafel polarization and impedance spectroscopy. The composite coating exhibited high charge transfer resistance (280.20 Ω.cm2) and low corrosion rate (6.54 × 10−6 mmpy) along with enhanced mechanical and tribological properties. The better performance of the composite coating was attributed to the combined ‘barrier-hydrophobic-sacrificial’ effect of the WO3-incorporated ZnAl coating.

Preparation of a wear-resistant, superhydrophobic SiO2/silicone-modified polyurethane composite coating through a two-step spraying method

The preparation of superhydrophobic coatings has been extensively researched, but their practical applications are limited by complicated preparation processes and poor mechanical durability. This study proposed a simple, low-cost method of preparing superhydrophobic coatings. A nano-silica dispersion was sprayed onto a semi-cured silicone-modified polyurethane resin through a two-step spraying method. Subsequently, these materials solidified together to successfully prepare a superhydrophobic coating with 159° contact angle and 2° sliding angle. The prepared silica/silicone-modified polyurethane (SiO2/SiPU) superhydrophobic coating showed superhydrophobic property after being cyclically rubbed for 30 cycles on 1000-mesh sandpaper under a load of 200 g. The coating further exhibited good corrosion resistance when placed in strong acid and alkali environments and excellent self-cleaning properties in air. This simple and environmentally friendly approach may have enormous application potential in many fields.

Mechanically durable superhydrophobic surfaces by binding polystyene nanoparticles on fibers with aluminum phosphate followed by hydrophobization

Mechanically durable superhydrophobic surfaces on cotton fabrics were fabricated by binding polystyrene nanoparticles onto fibers with aluminum phosphate (AP) followed by coating with polydimethylsiloxane (PDMS) as low surface energy substance. Decoration of nanoparticles roughened the fabric surface and coating with AP made stable the roughening structures. The as-prepared fabric surfaces not only showed excellent stability to acid, alkali, salt, organic solvent and UV irradiation, but also could maintain their superhydrophobicity after abrasion of 2000 or laundering of 35 cycles. The combination of inorganic adhesives AP and organic PDMS greatly enhanced the mechanical stability of the superhydrophobicty of the cotton substrate. Meanwhile, the obtained superhydrophobic fabrics showed excellent self-cleaning property.

Ultra-sensitive, reusable, and superhydrophobic Ag/ZnO/Ag 3D hybrid surface enhanced Raman scattering substrate for hemoglobin detection

The small Raman scattering cross section of hemoglobin (Hb) molecules limits its application using a Raman spectroscopy based optical biosensor. Label-free surface enhanced Raman scattering (SERS) detection and degradation of Hb have been achieved using 3D reusable superhydrophobic SERS substrates based on a Ag/ZnO/Ag hybrid structure. The fabrication process follows the decoration of thermally evaporated non-spherical like Ag nanoparticles on hydrothermally grown ZnO nanorods on a catalytic ultra-thin Ag film. From SERS point of view, these 3D SERS substrates exhibit four important characteristics such as a higher surface to volume ratio, surface plasmon resonance in the broad wavelength region of the visible spectrum, a strong electric field at the Ag–ZnO interface due to the formation of a Schottky barrier, and the superhydrophobic surface. The SERS substrates not only performed an outstanding Raman enhancement effect due to the above factors but also displayed multiple recyclabilities owing to their excellent self-cleaning property via a UV light assisted photocatalytic degradation process. The quantitative SERS analysis has been performed by a linear regression method and resulted in 10−13.42M and 10−7.24M limit of detection for Rhodamine 6G (Rh6G) and Hb molecules, respectively, with an enhancement factor of 6 × 1011. The effect of the 3D hybrid structure toward higher SERS activity has been compared with that of 2D SERS substrates, and the SERS mapping of Rh6G molecules proves good homogeneity of the 3D SERS substrates. These ultra-sensitive 3D SERS substrates with reusable capability open the possibility of their use toward biosensors for the early detection of diseases.

Multifunctional closed-pore silica/titania composite antireflective coatings based on self-assembly process

This paper reports multifunctional closed-pore silica/titania composite antireflective coatings (ARCs) prepared through combining with emulsion polymerization, sol-gel chemistry, electrostatic self-assembly, and calcination process. The ARCs show high transmittance, with maximum transmission of 98.1% at wavelength of 519 nm and the average transmittance in visible light region (400–700 nm) of 97.1%, a 7.0% increase compared with that of bare glass. Anatase nano titania decorated ARCs are obtained via controlling calcination temperature at 600 °C for 5 min and proved by XRD results. The ARCs exhibit excellent self-cleaning properties, illustrated by accelerating organic decomposition under UV and sunlight. Furthermore, the ARCs possess outstanding superhydrophilic and antifogging properties. In addition, water is the only solvent used in the whole process. These features make the method have specific advantages in the ARCs field.

A Durable and Self-Cleaning Superhydrophobic Surface Prepared by Precipitating Flower-Like Crystals on a Glass-Ceramic Surface.

Herein, a superhydrophobic surface with superior durability was fabricated on a glass-ceramic surface by crystallization, hydrofluoric acid (HF) etching, and surface grafting. The as-prepared glass-ceramic surface was composed of three-dimensional flower-like micro-clusters, which were self-assembled from numerous nanosheets. Such a dual-scale rough surface exhibited superhydrophobicity, with a water contact angle (WCA) of 170.3° ± 0.1° and a sliding angle (SA) of ~2° after grafting with 1H, 1H, 2H, 2H-perfluorodecyltriethoxysilane (FAS-17). This can be attributed to the synergistic effect between the dual-scale structure and surface chemistry. Furthermore, this surface exhibited excellent self-cleaning properties, stability against strong acid and strong alkali corrosion, and anti-stripping properties.

Silica and Silane based polymer composite coating on glass slide by dip-Coating Method

Superhydrophobic coatings are widely used for various engineering applications, namely, self-cleaning and self-healing for engineering structures. Therefore, in recent decades, a number of industries have shown significant interest in the development of superhydrophobic coatings for various purposes. In view of the above demands, this study presents explicitly a cost-effective and facile method to fabricate superhydrophobic transparent coating on the glass. The superhydrophobic coating was prepared by dip-coating technique with sol-gel of polymethyl methacrylate-co-ethyl acrylate polymer (PMMA), SiO2nanoparticles (SiNps) and 1H, 1H, 2H, 2H perfluorooctyltrichlorosilane (PFOTS). Wettability, surface morphology, and the transparency of coating were investigated. Also, the stability of the coating was assessed at harsh conditions like annealing at high temperatures (4–400 °C), irradiation by UV light, and pH resistance at different alkali and acidic conditions (2–13), and mechanical durability by performing water-jet, abrasion and adhesion tests were studied. The coated glass exhibits a static water contact angle (CA) of 174 ± 2° and with a sliding angle (SA) of 4 ± 1° Furthermore, the coating exhibits excellent self-cleaning property, and more than 91% of the transparency of the coating was assessed. All the results indicated that such type of coatings could also use for self-cleaning and transparent coatings at the industrial level.

Development of polyurethane-based superhydrophobic coatings on steel surfaces.

In this study, a superhydrophobic coating on steel surface has been developed with polyurethane, SiO2 nanoparticles and hexadecyltrimethoxysilane by using a spin-coating technique. Characterization of the coated steel surface was done by using the contact angle measurement technique, scanning electron microscopy and Fourier transform infrared spectroscopy. With a water tilt angle of 4° ± 2° and static contact angle of 165° ± 5°, the coated surface shows a superhydrophobic and self-cleaning nature. Chemical, thermal, mechanical stability tests and droplet dynamic studies were done to evaluate performance of the coating. Excellent self-cleaning, anti-fogging and anti-corrosion properties of coated steel surfaces make them ideal for industrial applications. This article is part of the theme issue 'Bioinspired materials and surfaces for green science and technology (part 3)'.

Robust TiO2 nanorods-SiO2 core-shell coating with high-performance self-cleaning properties under visible light

Photocatalytic SiO2–TiO2 composite coatings with excellent self-cleaning properties have attracted much attention in recent years due to their promising applications in many areas such as automobile windshields, window glasses, and solar cell panel covers, etc. However, most of these coatings are of low self-cleaning capability in the visible light region due to TiO2 only absorbing ultraviolet light, which limit their practical application. Here, highly transparent coatings of the rod-like TiO2–SiO2 nanoparticles on glass substrates were prepared by a simple dip-coating process. The photocatalytic activity and self-cleaning property of the coatings were evaluated by photocatalytic degradation of methylene blue (MB) and methyl stearate (MS) under visible light irradiation. It was found that the coatings exhibited ~4% enhancement in the optical transmission of glass and a good mechanical stability. The as-prepared and annealed rod-like TiO2–SiO2 nanoparticle coatings show excellent self-cleaning properties. The results mean that the coatings have a high potential for self-cleaning applications in removal of organic pollutants under visible light such as solar cell panels, architectural glasses and optical devices, etc.

Flexible TiO2/PVDF/g-C3N4 Nanocomposite with Excellent Light Photocatalytic Performance.

As the world faces water shortage and pollution crises, the development of novel visible light photocatalysts to purify water resources is urgently needed. Over the past decades, most of the reported photocatalysts have been in powder or granular forms, creating separation and recycling difficulties. To overcome these challenges, a flexible and recyclable heterostructured TiO2/polyvinylidene fluoride/graphitic carbon nitride (TiO2/PVDF/g-C3N4) composite was developed by combining electrospinning, sintering and hydrothermal methods. In the composite, PVDF was used as a support template for removing and separating the photocatalyst from solution. Compared with pure TiO2, the TiO2/PVDF/g-C3N4 composite exhibited the extended light capture range of TiO2 into the visible light region. The photogenerated carriers were efficiently transferred and separated at the contact interface between TiO2 and g-C3N4 under visible light irradiation, which consequently increased the photocatalytic activity of the photocatalyst. In addition, the flexible composites exhibited excellent self-cleaning properties, and the dye on the photocatalysts was completely degraded by the as-prepared materials. Based on the intrinsic low cost, recyclability, absorption of visible light, facile synthesis, self-cleaning properties and good photocatalytic performances of the composite, the photocatalyst is expected to be used for water treatment.

Functionalization of PET fabric via silicone based organic–inorganic hybrid coating

In this paper, silica dioxide nanoparticles (SiO2) were synthesized and functionalized with n-octadecyltriethoxysilane (OD) through a modified Stöber method for the preparation of organic–inorganic hybrid micro-nanoparticles. Organic–inorganic hybrid micro-nanoparticles were applied onto the polyester (PET) fabric via a conventional “dipping–drying” process for the fluoro-free water-repellent textile materials. The coated PET fabric surface showed micro/nano-structures and exhibited hydrophobic behavior with water contact angle of 141°. The surface morphologies, surface chemical composition and contact angles of the coated fabrics surface were measured. Furthermore, the dynamic hydrophobic behavior of water droplet impact on the fabric was investigated. By analyzing the energy change, D(t)/D0 value and H(t)/D0 value during water droplet impact were measured. The water droplet showed an obvious effect of the dynamic rebound behavior on the coated fabric surface, further confirming that the coated PET fabric had hydrophobicity. After the rubbing and washing durability, mechanical and chemical stability treatment, the coated PET fabrics still maintained high hydrophobicity and displayed good water-repellent durability. Last but not least, PET hydrophobic fabrics exhibited excellent self-cleaning properties with dyes on the fabric surface.

Development of stain resistant, superhydrophobic and self-cleaning coating on wood surface

In this work, hydrophilic (Dalbergia sissoo) wood has been modified into a superhydrophobic wood through simple immersion method using titanium dioxide (TiO2) nanoparticles and perfluorooctyltriethoxysilane (PFOTS). Wettability and surface topography of modified wood were characterized by contact angle measurement technique and scanning electron microscopy (SEM). Functional groups present on the modified wood surface were analysed by Fourier transform infrared spectroscopy (FTIR). Modified wood shows the excellent repellency to water and liquids with surface tension of more than 47 mN/m, with a static contact angle of more than 150° and tilt angle of less than 10°. Additionally, mechanical, thermal and chemical stability tests were also performed to evaluate wetting properties of superhydrophobic wood under harsh conditions. Furthermore, modified wood exhibits excellent self-cleaning and stain resistant properties, which makes it suitable for domestic and industrial applications.