Semitransparent Coatings Research Articles

Photothermal measurement of material properties for translucent thermal barrier coatings

In this study, a photothermal nondestructive method was proposed to measure the material parameters of semi-transparent or translucent thermal barrier coatings (TBCs). We derived a theoretical model for the photothermal signal from a two-layer semi-infinite material system with a translucent first layer after a pulse laser excitation. Its solution was verified by numerical solution. A data regression algorithm based on a least-squares fitting was used for the determination of the material parameters in the translucent first layer material. To verify this new method, an experimental system was set up with a pulse laser for thermal excitation and an infrared camera for image acquisition of the thermal emission transient from several translucent EBPVD TBC samples. The predicted coating thickness is consistent with the measured value by an optical microscope. The predicted thermal conductivity and optical attenuation coefficients in the absorption and emission band are found to be in good agreement with reference values.

Tailored self-assembly of semi-transparent polymer/clay nanocomposites for gas-barrier applications assisted by aqueous liquid crystalline scaffolds

A new strategy for preparing flexible and semi-transparent gas-barrier coatings was developed using tailored self-assembly of montmorillonite (MMT)/polyvinylpyrrolidone (PVP) nanocomposites assisted by aqueous liquid crystalline (LC) scaffolds. First, we established a composition wherein aqueous MMT exhibited the LC phase in the presence of polyethyleneimine (PEI) and hydrochloric acid (HCl). The viscoelastic rheological features of MMT LC enable the formation of uniform and conformal MMT coatings on various types of substrates, including flat or topographically featured surfaces. Moreover, the MMT LC serves as a structural scaffold that enables the rapid transport of PVP within the inner gallery space of the MMT LC, resulting in the formation of stacked MMT/PVP nanosheets after drying. Owing to its highly aligned layered structure, MMT/PVP exhibited flexible mechanical properties with enhanced hardness and modulus compared to neat MMT. Furthermore, the MMT/PVP can suppress gas permeation, as demonstrated by 0.1 Barrer of H2 permeability for the best coating conditions (containing 63 wt% MMT and 37 wt% PVP), while maintaining semi-transparent optical properties. Considering the aforementioned properties and that all components in MMT/PVP are bio-safe materials, this coating system has potential applications as a gas-barrier coating in conventional packaging materials, food packaging, and H2 storage tanks.

Independent transmitted and reflected colors enabled by Fano resonant optical coatings

Conventionally, optical coatings transmit and reflect the complementary colors due to the limitations of the resonant modes in multilayered structures. Here, we experimentally demonstrate a type of semi-transparent optical coating that can produce the same color in transmission and reflection based on Fano resonance. The results verify that when the metallic spacer is extremely thin, almost the same reflectance and transmittance spectra can be simultaneously achieved with the efficiency about 40%. Furthermore, we comprehensively explore the change of the colors by varying the thickness of the metal and the refractive index of the dielectric cap. Benefiting from the flexible tuning of the coupled resonator, a broad palette of colors and chromatic information display are presented. Our semi-transparent optical coatings exhibit viewing angle tolerance up to 40°, which may lead to novel display and optical anti-counterfeiting techniques.

Effective properties of semitransparent radiative cooling materials with spectrally variable properties

• Radiative cooling with semitransparent radiative coating and participating substrate. • Iterative method to calculate effective radiative properties from spectrally variable parameters. • Overall estimation error of less than 0.2%. • Beneficial for applications requiring lumped solar and thermal radiation related parameters. Radiative cooling is a promising solid-state, non-vapor-compression technology for passive refrigeration and air conditioning. Although this phenomenon occurs naturally, achieving a significant amount of cooling to make it a technically and economically viable technology requires highly engineered, spectrally selective radiative surfaces. These characteristics make radiative cooling difficult to estimate, particularly when it is integrated with other systems such as photovoltaic panels or building envelopes. The complexity further increases when the substrate also participates in the radiative cooling (along with the radiative coating). Energy estimation is becoming increasingly critical because of the recent focus on the semitransparent radiative coatings that transmit a variety of colors to enhance the aesthetic appeal of the system. Here, we propose an iterative method to calculate the effective radiative properties, which provides the same net radiative cooling that would be observed using the spectral properties at both the coating and substrate surfaces. Compared to traditional methods that rely on either computationally expensive full spectral analysis or methods for averaging each radiative surface parameter locally, our proposed method focuses on calculating effective properties that provide the same the net cooling effect as a full spectral analysis by accounting the emissivity, absorptivity, and transmissivity collectively, thereby providing an overall estimation error of less than 0.2%. We believe that this study will be beneficial to the engineering communities that employ complex simulation codes and require lumped solar and thermal radiation related parameters.

Dual-functional intumescent fire-retardant/self-healing water-based plywood coatings

Water-based fire-retardant coatings for wood are non-toxic, aesthetically pleasing, and can provide appreciable fire retardancy properties. However, excessive fire-retardant content and simple fire-retardant function limit their practical application. In this work, a semi-interpenetrating network (SIPN) technique was used to prepare a semi-transparent dual-functional, intumescent fire-retardant/self-healing water-based coating for plywood. The coatings comprised ammonium polyphosphate (APP) as a source of acid source and gas source; poly (vinyl alcohol) (PVA) as the carbon source and self-healing agent; and sodium silicate and sodium fluorosilicate (SS) as precursors for forming an integral inorganic network. Our semi-transparent coatings demonstrated excellent fire retardancy thanks to the interplay between the inorganic silicate network and the intumescent fire-retardant system. Remarkable self-healing properties were provided by the dynamic hydrogen bonding interaction between PVA molecular chains, where significant scratches were healed after exposure to water vapor. The PVA/SSA coating enhanced the fire retardancy of plywood, which was shown to be directly related to the APP content. The combination of semi-transparent, fire-retardant and self-healing capabilities underlines the potential of our PVA/SSA coatings for protecting and safeguarding wooden products.

Thickness Measurements of Clear Coatings on Silver Objects using Fiber Optic Reflectance Spectroscopy

ABSTRACT Polymer films have been used extensively to coat heritage metal objects to provide protection against atmospheric oxidation and tarnish. Coating performance is directly proportional to coating thickness, but current methods used to measure coating thickness for quality control during treatment are qualitative at best. This paper demonstrates how fiber optic reflectance spectroscopy (FORS) was used to accurately determine coating thicknesses on a number of nitrocellulose-coated silver objects at Winterthur Museum. FORS appears to be significantly more accurate than other common methods used to measure film thickness, such as magnetic/eddy current techniques, but is limited to transparent or semi-transparent coatings. FORS is a simple, accurate method for measuring the thickness of protective coatings on a wide range of cultural heritage metal objects.

Improvement of weatherability of semi-film-forming wood preservative semi-transparent coatings by laser micro incising

短パルスの紫外線レーザは木材表面に美観を損なわない微細な穿孔を開け，液体の浸透性を向上させるために有効である。ここではこの穿孔加工（レーザマイクロインサイジング）を応用し，半造膜形木材保護塗料で塗装した木材の屋外耐候性能の向上を試みた。 インサイジング試料における半造膜形塗料は含浸形塗料の分布と異なり，穿孔を充填しつつ塗膜を形成して投錨状の存在形態を示した。この塗布量は穿孔数や穿孔深さに依存して増加したが，半造膜形塗料の浸透が一定深さに留まるため，穴深さに対してレベルオフした。促進耐候性試験の結果，インサイジングによる塗布量の増加に伴い塗装木材の基材・塗膜割れが抑制された。また，塗装木材の変色や撥水度の低下も抑制され，レーザマイクロインサイジングにより半造膜形木材保護塗装の耐候性能が向上することが示された。

Poly(methyl methacrylate) Films with High Concentrations of Silicon Quantum Dots for Visibly Transparent Luminescent Solar Concentrators.

Silicon quantum dots (Si QDs) are attractive, nontoxic luminophores for luminescent solar concentrators (LSCs). Here, we produced Si QD/poly(methyl methacrylate) (PMMA) films on glass by doctor-blading polymer solutions and achieved films with low light scattering at an order of magnitude higher Si QD weight fraction than has been achieved previously in the bulk. We suggest that the fast solidification rate of films as compared to slow bulk polymerization is an enabling factor in avoiding large agglomerates within the nanocomposites. Scanning electron microscopy confirmed that ∼100 nm or larger QD agglomerates exist in light-scattering films, and photoluminescence intensity measurements show that light scattering, if present, significantly reduces waveguiding efficiencies for LSCs. Nonscattering films fabricated in this work exhibit high ultraviolet absorption (>80%) paired with high visible transmission (>87%) and minimal visible haze (∼1%), making them well suited for semitransparent coatings for LSCs realized as solar harvesting windows.

A Green Route to Prepare Semitransparent Superhydrophobic-Oleophobic Coatings

A series of coating samples were prepared with various combinations of solvents being tested via a two-step dip-coating route. The surface hydrophobicity was studied by measuring water and oil contact angles. Furthermore, the surface topography, optical and abrasive properties of the selected 4 coating samples were examined by atomic force microscopy (AFM), ultraviolet-visible spectrophotometer and friction cycle test, respectively. The best overall properties were achieved with the coating sample prepared by nontoxic epoxy resin-ethanol (Step 1) and isopropanol (Step 2). The water and oil contact angles reached 152.0° and 112.7°, respectively, and water contact angle remained 150.2° upon 5 cycles of the friction test with sandpaper. The transmittance of 80% was obtained in the wavelength ranging from 400 to 800 nm.

A new approach for preparation of semi-transparent superhydrophobic coatings by ultrasonic spray hydrolysis of methyltrimethoxysilane

A novel nebulizing spray hydrolysis approach was used for preparation of semi-transparent superhydrophobic coatings. Methyltrimethoxysilane was dissolved in water:ethanol mixture and ultrasonically sprayed on different substrates. Superhydrophobic coatings with a contact angle (CA) as high as 164° and a sliding angle below 5° were obtained. FESEM and AFM revealed a hierarchical micro-nano binary structure with nanometric roughness of the coatings. The coated glass substrate exhibited transmittance close to 80%. The prepared coating showed great self-cleaning and water jet repellency behaviors. The superhydrophobicity of the samples was remained after subjecting to ambient conditions for 50 days. The coating was also durable under water flushing test.

Durability of Selected Transparent and Semi-Transparent Coatings on Siberian and European Larch during Artificial Weathering

This paper compares the resistance of 20 commercial transparent and semi-transparent coatings applied to European and Siberian larch during artificial weathering in Xenotest. The change in gloss, colour, contact angle of wetting, resistance to Aspergillus niger and Penicillium brevicompactum moulds was evaluated, and visual changes at the top surface of treated wood species were measured. Overall, the durability of coatings on European larch was higher than that on Siberian larch. The most durable of the tested coatings was a thin-film, i.e., semi-transparent oil-based film containing TiO2 pigment and propiconazole fungicide. Of the transparent coatings, the most stable was a thick acrylic coating. Conversely, penetrating transparent oil systems had low colour stability and overall lifespan. Artificial weathering of all of the coatings resulted in a marked decrease in their resistance to moulds.

Modeling of the Structure of Heat-Insulating Semi-Transparent Materials and Coatings for Industrial and Transport Power Plants

The influence of optical characteristics of semitransparent thermal barrier coatings (TBC) on thermal regulation of heat-stressed elements of power plants is studied. There was used the developed by the authors methodology of physical and mathematical simulation of thermoradiational (in the range 1-2 μm) and conductive heat transmission in ceramic thermal insulation of chamber combustion inner walls of a diesel engine. The paper discusses temporal temperature regimes in model two-layer TBC-coatings in the form of a selectively scattering and absorbing (in the near infrared range) ceramic heat-insulating layer, deposited on the bonding sublayer (with boundary reflection) of the internal surface of the combustion chamber of Low Heat Rejection diesel. Spectrophotometric measurements of the optical parameters have ensured estimates of optical and thermal fields of the investigated ceramics, the structural composition of which was determined on the basis of ZrO2+8%Y2O3. For typical values of radiant-convective flux up to 1-2 MW/m2 (effecting on heat-stressed elements of heat-insulated combustion chamber of a diesel engine in pulse-periodic regime) optical and structural parameters TBC-coatings that ensure control and superintendence of the ceramic layer surface temperature and its temperature gradient were proposed.

Abrasion resistant semitransparent self-cleaning coatings based on porous silica microspheres and polydimethylsiloxane

Transparent, abrasion-resistant and superhydrophobic coatings have attracted considerable interest owing to their great advantages in applications. In this work, a semitransparent abrasion-resistant superhydrophobic coating was attained via depositing suspensions of porous silica microspheres and polydimethylsiloxane, followed by calcining and fluorating process. Herein, the porous silica microspheres were fabricated through a template method. Consequently, the coating exhibited a water contact angle of 153°, a hexane contact angle of 100° and an average optical transparency of 78%. Significantly, the coating displayed a robust resistance against sandpaper abrasion and knife-scratch. Furthermore, the coating also exhibited excellent self-cleaning performance even after it was contaminated by oil.

Method for emissivity measurement of semitransparent coatings at ambient temperature

Coatings deposited on a material surface are effective way of changing its surface properties. For increasing or decreasing radiation heat transfer, coatings with high or low emissivity are used. Measurement of spectral emissivity is a fundamental step to effective use of coatings for this application. Up to now the measurement methods are focused on bulk samples and mainly opaque ones. Here we present a method enabling measurement of emissivity of semitransparent coating itself, although it is deposited on a substrate. The method is based on measurement of transmittance and reflectance using an integration sphere system and Fourier transform infrared (FTIR) spectrometer for samples with two different coating thicknesses deposited on transparent substrates. Measured transmittance of the coating indicates spectral regions of potential emissivity differences using different substrates. From all the measured values, spectral emissivity can be characterized for different coating thicknesses. The spectral range of the method is from 2 μm to 20 μm. The measurement is done at ambient temperature enabling measurement of samples sensitive to heating like biomedical or nanocoatings. The method was validated on known bulk samples and an example of semitransparent coating measurement is shown on high-temperature high-emissivity coating.

水性木材保護塗料の耐候性能評価（Ⅳ）－塗替えによる寿命延長効果－

水性木材保護塗料について，塗替えによる寿命延長効果を検討した。既報において，スギまさ目試験片を水性６種類（半造膜形）と，比較対象として油性２種類（含浸形，半造膜形）の市販木材保護塗料で塗装し24ヶ月間の屋外暴露（暴露Ⅰ期）後，重ね塗り再塗装または研磨有再塗装を施し，再び屋外暴露試験（暴露Ⅱ期）を開始した。本報では，暴露Ⅱ期54～68ヶ月間（累計78～92ヶ月間）における試験片の色差と撥水度の変化を経時測定し，耐候性能を評価した。これらのデータから，寿命倍率（暴露Ⅱ期において撥水度または色差が寿命の目安に達するのに要する月数／暴露Ⅰ期において撥水度または色差が同目安に達するのに要する月数）を算出したところ，撥水度を指標とした場合，寿命倍率は重ね塗り再塗装で1.7倍，研磨有再塗装で2.3倍となり，研磨有再塗装で寿命延長効果が高いことが示された。また，塗替え前の性能順位と塗替え後の性能順位は比較的相関が高いことも明らかになった。

Ellipsometry of TiO_x coatings deposited in a magnetron apparatus with an unbalanced magnetic system: effect of the oxygen concentration and the magnetron–substrate distance

The method of spectral modulation ellipsometry is used to investigate the structure and optical properties of thin TiOx coatings deposited by magnetron with various oxygen concentrations in the plasma, a working pressure of 0.28 Pa, and a discharge current of 5.6 A. It is established that, depending on the fraction of O2, three types of coatings are formed in the plasma: semitransparent three-layer coatings, transparent two-layer coatings, and transparent three-layer coatings. The last coatings have a dense contact layer up to 50 nm thick, whose optical characteristics correspond to crystalline anatase and/or rutile. A correlation is established between the roughness, the band gap, and the impurity concentration in the plasma. It is pointed out that, with 19 vol. % O2, coatings with a low refractive index (2.347), a small band gap (3.31 eV), and high roughness (16.8 nm) are deposited in the plasma, and this must increase the photocatalytic activity of the coatings.

Semitransparent superoleophobic coatings with low sliding angles for hot liquids based on silica nanotubes

Semitransparent superoleophobic coatings with low sliding angles for hot liquids are successfully prepared by fabrication of silica nanotubes on glass slides, and then modification with 1H,1H,2H,2H-perfluorodecyltrichlorosilane.

木材保護塗料の耐候性能評価－市販塗料43種類の屋外暴露４年間の性能変化－

木材保護塗料の耐候性能評価－市販塗料43種類の屋外暴露４年間の性能変化－

木材保護塗料の耐候性能向上に及ぼす素地粗面化処理の影響

木材保護塗料の耐候性能向上に及ぼす素地粗面化処理の影響

Development of sol–gel processed semi-transparent and self-cleaning superhydrophobic coatings

The formation of an air-column on a superhydrophobic surface: the superhydrophobic coating is surrounded by blue colored water forming an air column, and water acquires a height of nearly 5 mm around the boundaries of the superhydrophobic coating. This confirms that the superhydrophobic surface strongly repels water and always remains dry.