Transparent Coatings Research Articles

Synthesis and application of manganese dioxide nanoparticles as part of anti-corrosion coatings

The paper presents a study of synthesized manganese dioxide nanoparticles effect on the properties of transparent coatings to protect the rolled metal from corrosion. Capacitive-ohmic measurements of the electrochemical cell formed on the studied coatings demonstrate corrosion processes inhibition under the coating with a nanoparticle content of 0.025% and higher.

Fundamental mode emission in tapered quantum cascade lasers for high brightness

Currently, the highest power quantum cascade lasers (QCLs) include (i) an efficient active region design, which minimizes the energy fraction transferred into heat, (ii) a relatively large number (40) of cascades, which increases the mode confinement factor, Γ, and (iii) narrow buried-heterostructure waveguides, which efficiently cool the active region through efficient lateral heat flow. This combination allows watt-level continuous wave (cw) emission powers at room temperature. Moreover, narrow waveguides favor the fundamental TM00 lateral mode, resulting in a nearly Gaussian beam. To the extent that power efficiency is already largely optimized, power scaling in narrow-stripe QCLs is only possible through increasing the laser length, which is limited by the needs for robust construction and transparent antireflection coatings. Broad-area (BA) QCLs with a small number of cascades can also deliver watt-level cw powers at room temperature, profiting from the enhanced vertical heat flow. Power can be scaled for these lasers also via the laser width and is nearly unlimited. The usual drawback of the BA lasers is poor beam quality. We discuss the use of tapered QCLs and the first demonstration of room temperature cw operation of the BA QCL in fundamental TM00 mode. A stable and reproducible transverse optical mode is achieved using a double-taper waveguide geometry. The laser emits at 4.6 μm and has a demonstrated room temperature cw power of 100 mW.

Self-cleaning material based on superhydrophobic coatings through an environmentally friendly sol–gel method

Recently, there has been increasing interest in developing artificial superhydrophobic surfaces, especially in the field of self-cleaning application. However, the poor robustness and high-cost preparation of these surfaces have always been some issues for their industrial development. Herein, we describe an environmentally friendly way to prepare stable, robust, and transparent superhydrophobic coatings through the deposition of a rough substructure of TiO2 film followed by chemical modification using octadecyltrichlorosilane (OTS), a fluorine-free organic silane. The as-prepared coatings exhibited a great superhydrophobic property and ultralow adhesion (with a static water contact angle of 158 ± 2° and sliding angle of 4 ± 1°). It was found that the superhydrophobic coatings can still maintain good performance after UV irradiation, chemical immersion, and physical abrasion. More importantly, the coated surfaces showed an excellent self-cleaning ability against dirt particles after rinsed with water droplets.

Ultrasonic Spray Pyrolysis of Antimony‐Doped Tin Oxide Transparent Conductive Coatings

AbstractTransparent conducting oxides are fundamental for the fabrication of optoelectronic devices including touchscreen displays, solar cells, and light emitting diodes. However, they mostly rely on rare elements and expensive vacuum‐based deposition methods that negatively affect the overall cost of optoelectronics. Here, a detailed investigation on the synthesis of antimony‐doped tin oxide films using an ultrasonic spray coating system is presented. High‐quality, crystalline SnO2 films are deposited via decomposition of metal precursors sprayed directly onto hot (>400 °C) substrates. Doping is easily achieved by adding the dopant salt to the spray solution, and the presence of the dopant atoms heavily influences the optical, electrical, and structural properties of SnO2. These coatings are characterized using a comprehensive suite of techniques including X‐ray diffraction, electron microscopy, X‐ray and ultraviolet photoelectron spectroscopies, Hall effect measurements, optical spectroscopy in the visible and near infrared, and atomic force microscopy, in order to elucidate the relationship between the synthetic conditions and functional properties. Through a careful optimization process, Sb‐doped SnO2 coatings showing transmittance values in the visible spectrum between 80% and 90%, and sheet resistances of 10–20 Ω/sq−1 are achieved. Such values are suitable for immediate applications of these Sb‐doped SnO2 films as high‐performance transparent conductors.

Green preparation of transparent superhydrophobic coatings with persistent dynamic impact resistance for outdoor applications

Transparent superhydrophobic surfaces are employed in a wide range of outdoor applications, such as windshields and house windows. However, micro-nano hierarchical superhydrophobic structures are vulnerable to impacts from sand particles and rain drops. The low impact resistance limits the practical applications of superhydrophobic surfaces. Herein, we develop a novel eco-friendly self-assembly process in aqueous medium to construct transparent superhydrophobic surfaces with high dynamic impact resistance. The transmittance of the prepared surfaces was ~ 94.2% compared with the transmittance of the pure glass substrate. The surface is resistant to the impact of 600 g sand and an ~ 8.6 m/s of water jet applied for 6 min (this is nearly 1500 times higher than the annual precipitation in the tropics), which makes the superhydrophobic surface sustainable in heavy rain. Furthermore, the coating was resistant to highly corrosive media (sulfuric acid) in the case of acid rain and UV illumination. A combination of these properties is attractive for transparent applications with self-cleaning properties, waterproofing and environmental stability.

Nonfluorinated, transparent, and spontaneous self-healing superhydrophobic coatings enabled by supramolecular polymers

Transparent self-healing superhydrophobic coatings have important applications on lenses, solar cells, helmet visors, and windshields et al. However, their applications at the present stage are limited by hazardous fluorinated materials, low transmittance, and heating treatment for healing. In this study, nonfluorinated, transparent, and superhydrophobic coatings with spontaneous self-healing ability are successfully fabricated via spray coating an ethanol solution of polydimethylsiloxane (PDMS)-based supramolecular polymer cross-linked via N-coordinated boroxines (N-Boroxine-PDMS) and SiO2 nanoparticles. Benefiting from the use of spray-coating technique, the transparent self-healing superhydrophobic coatings can be readily applied to various substrates such as plastic spectacle lens, wood, metal, and paper, greatly expanding the scope of applications. The obtained coatings possess good transparency with a transmittance at 550 nm of 90.1% and excellent superhydrophobicity with a contact angle of 160.9° and a sliding angle of 1°, which can be attributed to the use of N-Boroxine-PDMS that is inherently transparent and hydrophobic. The N-Boroxine-PDMS/SiO2 coatings can withstand water impact, UV irradiation, and heating at elevated temperatures due to the use of N-Boroxine-PDMS. More importantly, the coatings are capable of repetitively and spontaneously healing the chemical damage caused by exposure to hydrogen peroxide or O2 plasma at room temperature because the reversibility of N-coordinated boroxines allows the oligomers of N-Boroxine-PDMS readily migrate to the damaged surface. Our finds show evidence that the use of properly designed supramolecular polymers as coating materials provides a simple and effective way to simultaneously integrate good transparency, stability, and spontaneous room-temperature self-healing ability in superhydrophobic coatings.

UV cured transparent coatings with good thermal stability prepared from a liquid polyhedral oligomeric silsesquioxane with allyl sulphur−containing carbosilane substitutes

It is necessary to develop novel silicone materials with high transparency and excellent thermal stability to meet increasing demands from demands from next generation electronic devices. Polyhedral oligomeric silsesquioxane (POSS) was widely used to improve thermal properties of silicone materials, however, when solid POSS derivatives were used, the toxic organic solvents are needed to facilitate the dispersion of POSS, which will inevitably hinder the practical application. To overcome these shortcomings, a kind of liquid POSS with allyl sulphur−containing carbosilane substitutes was fabricated to improve thermal stability of transparent silicone coatings prepared by UV initiated thiol–ene reaction. These silicone materials exhibit transparency higher than 88 % (400–800 nm). The coatings also show transmittance higher than 80 % (400−800 nm) even being immersed in acid(10 wt% HCl) and salt(10 wt% NaCl) aqueous for 20 days. TGA analysis shows the start thermal decomposition temperature and the degradation residual yield at 800 °C under N2 atmosphere are as high as 337.2–377.9 °C and 51.7–60.8 % respectively. By comparison with the materials improved thermal properties by POSSs reported previously, the materials obtained also have excellent thermal stability. It can be concluded that it is a good method to improve thermal stability of silicone materials by combining the advantages of liquid POSS and carbosilane.

Power supply efficiency in dual magnetron large area sputter coatings

In large area sputter coating of glass, the consumption of electric power is one of the major cost drivers. This applies especially to dielectric transparent coatings which are relatively thick and for which sputter yields and rates can be rather low. These materials are usually sputtered from dual magnetrons using medium frequency (sine wave) or bipolar (square wave) power supplies at frequencies up to 100 kHz. Frequencies at 50 kHz or higher are beneficial for suppressing arcing on the target surface, and the power required to achieve viable sputter rates is often high, making the power consumption a significant cost contribution. In this study we look at the effect of the power supply technology and frequency on the sputter rate and the sputtered layer thickness per electrical energy input. The tests were carried out with aluminum dual planar targets and with TiOx dual rotary targets. At low frequencies around 20 kHz, the bipolar generator can yield about 10% higher sputtering rates at the same input power. At about 40 kHz, which is often chosen to minimize arcing, the rates from the two power supplies are about equal.

Preparation of High Hardness Transparent Coating with Controllable Refractive Index by Sol-Gel Technology

SiO2/ZrO2 and SiO2/ZrO2/Al2O3 composite organic–inorganic coatings were prepared by the sol-gel technology. The structure of the coating was characterized by IR, particle size analyzer, SEM, and AFM, respectively. The results showed that ZrO2, SiO2 (inorganic component), and siloxane had undergone a hydrolytic condensation reaction, and the composite organic–inorganic coatings were formed with -O-M-O- (M is Si, Zr) as molecular skeleton network structure. Adding an appropriate ratio of ZrO2 sol, no agglomeration and phase separation occurred, which could significantly improve the refractive index, hardness, and light transmittance of the coatings. Al2O3 sol could greatly improve the friction resistance of the composite organic–inorganic coatings, and the Bayer ratio of the composite coatings could reach 7.86. By adjusting the proportioning of composite sol solution, the refractive index of the composite transparent coatings could be controlled from 1.52 to 1.65.

A facile approach to durable, transparent and self-healing coatings with enhanced hardness based on Diels-Alder polymer networks

Prolonged durability in outdoor environment and ease of application are highly required features for self-healing coatings. To this end, a novel transparent and self-healing nanocomposite for optical applications, based on Diels-Alder (DA) chemistry is developed in this work. First, a novel, highly soluble, bismaleimide enabled a simple coating fabrication by coupling with furan-functionalized polyacrylates in industrially relevant solvents. The resulting crosslinked coatings exhibited high transparency and complete absence of color, as assessed by UV–vis spectroscopy. Their thermal behavior and the conditions required by the healing process were significantly affected by the degree of furan/maleimide functionality of the system. Secondly, the addition of a small amount of a commercial antioxidant stabilized the optical properties against photo-oxidative weathering, both on clear and titania-pigmented coatings, as determined by colorimetric analysis. Finally, dispersion of silica nanoparticles in the DA-based matrix allowed to enhance the surface hardness of the coatings, while retaining the self-healing ability.

Optically and radio frequency (RF) transparent meta-glass

Abstract We propose a radio frequency (RF) and visibly transparent composite metasurface design comprising newly developed transparent multilayer conductive coatings. Detailed experimental and theoretical analysis of the RF/visible transparency of the proposed meta-glass is provided. The proposed nature-inspired symmetrical honeycomb-shaped meta-glass design, alters the electromagnetic properties of the glass substrate in the RF spectrum by utilizing visibly transparent Ag-based conductive coatings on each side. Furthermore, the competing effect of the Ag thickness on optical and RF transparency is discussed. We show that using multilayer dielectric-metal coatings, specifically 5-layered spectrally selective coatings, RF transparency of the meta-glass can be enhanced while preserving visible transparency. Herein we demonstrate high transparency meta-glass with 83% and 78% peak RF and optical transmission at 28 GHz and 550 nm, respectively. The meta-glass yields enhanced RF transmission by 80% and 10% when compared to low-emissivity glass and bare glass, respectively. The meta-glass design presented here is amenable to a variety of 5G applications including automobile radar systems. This work provides a superior alternative to the standard indium-tin-oxide (ITO) transparent material which is becoming scarce. Moreover, this study paves the way for the design of new visibly transparent metamaterials and artificial dielectrics.

Dehydrogenation-driven assembly of transparent and durable superhydrophobic ORMOSIL coatings on cellulose-based substrates

A novel dehydrogenation-driven assembly method was proposed to fabricate durable superhydrophobic SiO2/PMHS ORMOSIL (organically modified silica) coatings on cellulose-based substrates. Poly(methylhydrogen)siloxane (PMHS) played the key role in the durability of ORMOSIL coatings and the assembly process. The dehydrogenation-driven assembly mechanism of ORMOSIL was discussed in detail. Results indicated that the chemical property and microstructure of ORMOSIL could be controlled easily by varying the weight ratio of SiO2 to PMHS. The lotus-like ORMOSIL coating could be realized as the weight ratio of SiO2 to PMHS was 1:1. The ORMOSIL coating on wood surface was of self-cleaning property, good transparency and durability (including water-repellency and dimensional stability, mechanical and chemical stability, and UV-resistance). In addition, the SiO2/PMHS ORMOSIL gave cotton good oil/water separation ability. Finally, the dehydrogenation-driven assembly method was simple and low-cost, and it can be applied to fabricate durable superhydrophobic coatings on any other hydroxyl-containing substrates besides the cellulose-based substrates.

Fabrication of Transparent UV-Cured Coatings with Allyl-Terminated Hyperbranched Polycarbosilanes and Thiol Silicone Resins.

To improve thermal stability and hardness of UV-cured materials, a series of UV-cured solvent-free coatings were prepared from allyl-terminated hyperbranched polycarbosilanes and thiol silicone resins. The silicone coatings prepared have pencil hardness of 4–9 H, water absorption no more than 0.04 wt %, and transmittance higher than 94%. The temperature for the coatings’ starting thermal decomposition is higher than 236 °C; especially, that of the coating prepared with G1 is as high as 371.1 °C. The UV-cured coatings in this work exhibit much higher pencil hardness than and superior thermal stability to those reported previously.

Synthesis and characterization of optically transparent ceramic crystalline/amorphous and amorphous/amorphous multilayers

Optical nano multilayers (NMs) are promising candidates for durable transparent multifunctional coatings, where the contributions of interfaces and high transparency configurations have yet to be explored. To address this, high transparency NMs (%T380-1100nm≈94–99%) were synthesized by magnetron sputtering, and the effects of crystalline/amorphous (AlN/SiO2, AlN/Al2O3) and amorphous/amorphous (TiO2/SiO2) interfaces were characterized by spectrophotometry, transmission electron microscopy, and nanoindentation. We demonstrate that tuning layer configurations for improved transmittance resulted in substantial variations in microstructure and multifunctional film properties. Overall, this work presents a methodology for evaluating the structure-properties relationship in optical NMs in the context of interface character and layer microstructure.

Covalently grafted liquids for transparent and omniphobic surfaces via thiol-ene click chemistry

Here, a robust omniphobic slippery surface with excellent transparency was fabricated on ultrasmooth glass by thiol-ene click chemistry without pretextured rough structure. The original glass after alkaline hydrothermal treatment could form massive hydroxyl group, which acted as the reactive sites could occur dehydration condensation reaction with the 3-mercaptopropyltrimethoxysilane. Then, the vinyl-terminated polydimethylsiloxane (PDMS) covalently grafted onto the mercapto-modified glass via the facile and efficient thiol-ene click chemistry. The prepared surface exhibited superior transparency, omniphobicity and anti-fouling property. Moreover, the tethered PDMS monolayer displayed durable liquid-repellent property after long-term storage in high/low temperature, UV irradiation, water impaction and mechanical abrasion tests. Thus, such covalent grafting strategy for constructing omniphobic and transparent coatings without the assistant of the textured rough structure could promote the advancement of interfacial antiwetting materials. A highly transparent omniphobic coating was prepared by covalently grafting of vinyl-terminated PDMS onto the mercapto-modified surface via a thiol-ene click reaction. This PDMS-silicone oil-grafted surface exhibited high transparency and performed good antifouling property and liquid repellency even to the ethanol. Furthermore, the covalent grafting strategy endows the lubricating layer with excellent stability and mechanical durability to various external destructions.

Electrostatic assembly functionalization of poly (γ-glutamic acid) for biomedical antibacterial applications

Poly (γ-glutamic acid) (γ-PGA) has been found widespread applications in biomedical field because of its excellent water solubility, biocompatibility, and bioactivity. Herein, a water-insoluble γ-PGA antibacterial compound is facilely fabricated via one-pot electrostatic assembly of γ-PGA with cationic ethyl lauroyl arginate (ELA). The functionalized γ-PGA compound (γ-PGA-ELA) ethanol solution can facilely produce colorless and transparent coatings on various inorganic, metal, and polymeric substrates, especially for the lumen of slender catheters (length up to 2 m, and inner diameter down to 1 mm). The functionalized γ-PGA coating presents remarkable antibacterial efficacy in vitro and in vivo. In addition, the γ-PGA compound is used as antibacterial additives of polyolefin via melting extrusion, and the as-prepared antibacterial polyolefin demonstrates advantageous antibacterial efficacy. More importantly, the functionalized γ-PGA coating exhibit good hemocompatibility, low cytotoxicity, and satisfactory histocompatibility. The as-proposed γ-PGA compound has a great potential to serve as a safe and multifunctional antibacterial candidate to combat biomedical devices-related infections.

Fabrication of transparent clay-polymer hybrid coatings on PET film to enhance flame retardancy and oxygen barrier properties

A multifunctional nanocoating, consisting of montmorillonite (MMT) / laponite (LAP) / polyvinyl alcohol (PVA), was deposited onto the surface of polyethylene terephthalate (PET) film via a facile co-assembly process. As a result, the PVA/LAP/MMT coating endowed PET film with improved flame retardancy and oxygen barrier. At 4 layers deposition of PVA/LAP/MMT, the film maintained more than 90% transmittance to the visible light. The microscale combustion calorimetry revealed, compared with control PET sample, the peak of heat release rate and total heat release of PET@(MMT/LAP/PVA)4 sample were reduced by 67.4% and 45.3%, respectively. The oxygen transmission rate significantly reduced at the same time. The reason was speculated at the combination of MMT and LAP, a more compact shielding layer was formed on the PET substrate.

Highly Transparent Covalent Mucin Coatings Improve the Wettability and Tribology of Hydrophobic Contact Lenses.

A stable, good coverage of the corneal tissue by the tear film is essential for protecting the eye. Contact lenses, however, constitute a foreign body that separates the tear film into two thinner layers, which are then more vulnerable toward disruption. This effect is even more pronounced if the contact lenses possess an insufficient surface wettability, which, in addition to friction, is suggested to be linked to discomfort and damage to the ocular surface. In this study, we establish covalent surface coatings with mucin macromolecules to overcome this issue for pure silicone contact lenses. This material class, which outperforms state-of-the-art silicone hydrogels in terms of oxygen permeability, is not yet used for commercial contact lens applications, which is due to its strongly hydrophobic surface characteristics. The applied process stably attaches a transparent mucin layer onto the contact lenses and thereby establishes hydrophilic surfaces that not only prevent lipid adsorption but also interact very well with liquid environments. Most importantly, however, we show that those mucin coatings are indeed able to prevent wear formation on corneal tissue that is subjected to the tribological stress applied by a contact lens. Our results open up great possibilities for a variety of hydrophobic materials that are, to date, not suitable for a contact lens application. Furthermore, the ability of mucin coatings to reduce wear in a tissue/synthetic material contact might be also beneficial for other biomedical applications.

Fabrication of Robust and Transparent Slippery Coating with Hot Water Repellency, Antifouling Property, and Corrosion Resistance.

Water-repellent coatings with low sliding angles for aqueous liquids are of great significance for practical applications. However, these coatings are susceptible to various types of damage during service and lose their effect. Herein, a robust and transparent slippery coating with extremely low water sliding angle was fabricated by covalently grafting polydimethylsiloxane (PDMS) brushes in a cross-linked skeleton of epoxy resin. Polyamidoamine G5.0 with 128 NH2 end groups was used as curing agent to induce the high cross-linking of the coating and the abundant PDMS brushes being grafted into it. Because of low surface energy and high mobility of PDMS brushes, the obtained coating exhibited a slippery performance for aqueous liquids (10 μL) with a sliding angle lower than 3° and a sliding speed as high as 1.16 mm/s. Even a 10 μL water droplet with temperature of 80 °C can slide off the coating at a low sliding angle (<5°). The strong intermolecular interactions of epoxy cross-linked skeleton endowed the coating with excellent physical and chemical stability. The sliding angle of the coating had no obvious change after heating at 120 °C for 100 h and placing outdoors for 7 months. The slippery performance was not affected by thumb press, knife scratching, high-speed friction, and water of different pH values. Furthermore, because of the excellent stability, antifouling performance, and corrosion resistance, the slippery coating can be applied to a variety of substrates, which makes the robust slippery coating have real potential for practical applications.

Improving water resistance of waterborne polyurethane coating with high transparency and good mechanical properties

Polyester based waterborne polyurethane (WPU) dispersions modified with hydroxypropyl-terminated polydimethylsiloxane (HPDMS) and sulfonate polyester diol were synthesized. The water resistance of WPU coating improved significantly when 5% HPDMS was used for modification, but it also leads to the decreasing of dispersion stability and damages in the mechanical properties and transparency of WPU coating. It was found that incorporating ionic groups in soft segments (sulfonate polyester diol) of WPU can obtain a coating with good water resistance where only 0.5% HPDMS is needed. In this case, the water swelling of WPU coating decreased to 7.0% while the pure WPU was 15.2%. Meanwhile, the mechanical and optical properties of modified coating change slightly. Its tensile strength was 62.6 MPa, and its light transmittance at 532 nm was 83.8%. Zeta potential test indicated the introduction of sulfonate polyester diol could improve the stability of WPU dispersions. The water resistance improvement of the WPU coating could be ascribe to the decrease of surface free energy and the change of phase separation degree. The water swelling, X-ray photoelectron spectroscopy, and contact angle test results demonstrated the migration of HPDMS and sulfonate polyester diol segments on the coating surface. The phase separation of WPU coatings was measured by dynamic thermomechanical analysis. The modified WPU with excellent water resistance is promising in the application of transparent coatings.