Coatings

19 pages, 1332 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Active Casein Coatings and Films for Perishable Foods: Structural Properties and Shelf-Life Extension

by Muhammad Rehan Khan, Stefania Volpe, Marika Valentino, Nicoletta Antonella Miele, Silvana Cavella and Elena Torrieri

Coatings 2021, 11(8), 899; https://doi.org/10.3390/coatings11080899 - 28 Jul 2021

Cited by 57 | Viewed by 7842

Abstract

There is an urgent need to increase the food supplies to fulfil the demands of future generations as the population of the world is expected to grow beyond 10 billion by 2050. An essential component for ensuring global food security is to reduce [...] Read more.

There is an urgent need to increase the food supplies to fulfil the demands of future generations as the population of the world is expected to grow beyond 10 billion by 2050. An essential component for ensuring global food security is to reduce food losses during the post-harvest stage. Active edible coatings and films are a promising sustainable preservation technology for shelf-life extension of food products by hindering decay kinetics of minimally processed fruits and vegetables (F&V), by restricting the mass transfer of moisture, aroma, or gases and carrying an active compound, such as an antioxidant or antimicrobial. Active protein-based coatings and films have the potential to extend the shelf-life of food products by decreasing their respiration rates, as they exhibit an excellent gas barrier and good mechanical properties as compared to other biopolymeric packaging. Among protein-based biopolymers, casein and its derivatives as packaging films have been extensively studied due to their low cost, complete biodegradability, and availability. Currently, there is no review study focusing on caseinate-based active coating and film, thus, this review aims to give insights on the composition, rheology, structure, and properties of caseinate-based formulations by critically discussing the results presented in the literature. A methodological approach was followed to obtain relevant literature to discuss the influence of additives on the shelf-life of F&V. Furthermore, changes in secondary structure of casein were observed after incorporation of bioactive compounds (i.e., phenolic acids). Likewise, there is a need to explore chemical interactions among bioactive compounds and biopolymer material by using in silico and laboratory trials as food additives have shown to influence the physicochemical properties of film and shelf-life of food products. Full article

(This article belongs to the Special Issue Biopolymer Coatings for Food Packaging Applications)

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12 pages, 4428 KiB

Open AccessEditor’s ChoiceArticle

Based on Ultrathin PEDOT:PSS/c-Ge Solar Cells Design and Their Photoelectric Performance

by Ju Su, Hua Yang, Yan Xu, Yijun Tang, Zao Yi, Fusheng Zheng, Fei Zhao, Li Liu, Pinghui Wu and Hailiang Li

Coatings 2021, 11(7), 748; https://doi.org/10.3390/coatings11070748 - 22 Jun 2021

Cited by 29 | Viewed by 4201

Abstract

In recent years, nanostructures have improved the performance of solar cells and are regarded as the most promising microstructures. The optical properties of PEDOT:PSS/c-Ge hybrid solar cells (HSCs) based on the octagon germanium nanoparticles (O-GNPs) were numerically analyzed using the finite-difference time-domain (FDTD) [...] Read more.

In recent years, nanostructures have improved the performance of solar cells and are regarded as the most promising microstructures. The optical properties of PEDOT:PSS/c-Ge hybrid solar cells (HSCs) based on the octagon germanium nanoparticles (O-GNPs) were numerically analyzed using the finite-difference time-domain (FDTD) method. The optimal structure of the hybrid solar cell is determined by changing the thickness of the organic layer and structural parameters of nanoparticles to enhance the optical absorption and eventually achieve high broadband absorption. By changing the structure parameter of O-GNPs, we studied its effect on solar cells. The optimization of geometric parameters is based on maximum absorption. The light absorption of our optimized HSCs is basically above 90% between 200 and 1500 nm. PEDOT:PSS is placed on top of O-GNPs to transmit the holes better, allowing O-GNPs to capture a lot of photons, to increase absorbance value properties in the AM1.5 solar spectral irradiated region. The transmittance is increased by adding poly-methyl methacrylate (PMMA). At the same time, the electrical characteristics of Ge solar cells were simulated by DEVICE, and short-circuit current (Jsc), open-circuit voltage (Voc), maximum power (Pmax), filling coefficient (FF) and photoelectric conversion efficiency (PCE) were obtained. According to the optimization results after adjusting the structural parameters, the maximum short-circuit current is 44.32 mA/cm²; PCE is 7.84 mW/cm²; FF is 69%. The results show that the O-GNPs have a good light trapping effect, and the structure design has great potential for the absorption of HSCs; it is believed that the conversion efficiency will be further improved through further research. Full article

(This article belongs to the Special Issue Micro-Nano Optics and Its Applications)

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12 pages, 5635 KiB

Open AccessEditor’s ChoiceArticle

Facile Synthesis of Copper(I) Oxide Nanochains and the Photo-Thermal Conversion Performance of Its Nanofluids

by Zhongjin Ni, Xiaohai Cao, Xinyi Wang, Shiyu Zhou, Caixia Zhang, Bin Xu and Yihua Ni

Coatings 2021, 11(7), 749; https://doi.org/10.3390/coatings11070749 - 22 Jun 2021

Cited by 71 | Viewed by 4288

Abstract

In this thesis, Cu₂O nanochains were synthesized by thermal decomposition with copper formate-octylamine as the precursor, oleic acid and oleylamine as the catalyst stabilizer agent and paraffin as the solvent. The phase structure and micromorphology of Cu₂O nanochains were [...] Read more.

In this thesis, Cu₂O nanochains were synthesized by thermal decomposition with copper formate-octylamine as the precursor, oleic acid and oleylamine as the catalyst stabilizer agent and paraffin as the solvent. The phase structure and micromorphology of Cu₂O nanochains were characterized by X-ray diffraction and transmission electron microscopy. The effect of reaction time and concentration of the precursor on the Cu₂O nanochains were discussed, and the formation mechanism of the Cu₂O nanochains was analyzed. The results show that Cu₂O nanochains were self-assembled by Cu₂O nanocrystals; with the extension of the reaction time, Cu₂O nanochains gradually become granular; increasing the concentration of the precursor will increase the entanglement degree of the nanochains. Oleic acid contributes to the formation of Cu₂O, and oleylamine plays a directional role in the formation of nanochains. On the basis of those phenomenon, a comparison of the Cu₂O nanochain-water nanofluids with that of a water-based liquid showed that after irradiating for 3000 s, the temperature of nanofluids reached 91.1 °C while the water was only 75.7 °C. This demonstrates the better performance of the Cu₂O nanochain-water nanofluid in the ability of light absorption, thermal conductivity and photothermal conversion. Full article

(This article belongs to the Special Issue Corrosion and Degradation of Materials)

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19 pages, 2875 KiB

Open AccessFeature PaperEditor’s ChoiceReview

High Pressure X-ray Diffraction as a Tool for Designing Doped Ceria Thin Films Electrolytes

by Sara Massardo, Alessandro Cingolani and Cristina Artini

Coatings 2021, 11(6), 724; https://doi.org/10.3390/coatings11060724 - 16 Jun 2021

Cited by 3 | Viewed by 3135

Abstract

Rare earth-doped ceria thin films are currently thoroughly studied to be used in miniaturized solid oxide cells, memristive devices and gas sensors. The employment in such different application fields derives from the most remarkable property of this material, namely ionic conductivity, occurring through [...] Read more.

Rare earth-doped ceria thin films are currently thoroughly studied to be used in miniaturized solid oxide cells, memristive devices and gas sensors. The employment in such different application fields derives from the most remarkable property of this material, namely ionic conductivity, occurring through the mobility of oxygen ions above a certain threshold temperature. This feature is in turn limited by the association of defects, which hinders the movement of ions through the lattice. In addition to these issues, ionic conductivity in thin films is dominated by the presence of the film/substrate interface, where a strain can arise as a consequence of lattice mismatch. A tensile strain, in particular, when not released through the occurrence of dislocations, enhances ionic conduction through the reduction of activation energy. Within this complex framework, high pressure X-ray diffraction investigations performed on the bulk material are of great help in estimating the bulk modulus of the material, and hence its compressibility, namely its tolerance toward the application of a compressive/tensile stress. In this review, an overview is given about the correlation between structure and transport properties in rare earth-doped ceria films, and the role of high pressure X-ray diffraction studies in the selection of the most proper compositions for the design of thin films. Full article

(This article belongs to the Special Issue Functional Oxide Thin Films and Nanostructures: Growth, Properties, and Applications)

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12 pages, 2377 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Plasma Enhanced-Chemical Vapor Deposition of 2-Isopropenyl-2-Oxazoline to Promote the Adhesion between a Polyethylene Terephthalate Monofilament and the Rubber in a Tire

by Carlo Maria Gaifami, Stefano Zanini, Luca Zoia and Claudia Riccardi

Coatings 2021, 11(6), 708; https://doi.org/10.3390/coatings11060708 - 12 Jun 2021

Cited by 3 | Viewed by 3376

Abstract

A Plasma-Enhanced Chemical Vapor Deposition was chosen in order to deposit an organic thin film on polyethylene terephthalate monofilament to increase its adhesion with the rubber compound in a tire. The aim of the work is to find an alternative “green” method to [...] Read more.

A Plasma-Enhanced Chemical Vapor Deposition was chosen in order to deposit an organic thin film on polyethylene terephthalate monofilament to increase its adhesion with the rubber compound in a tire. The aim of the work is to find an alternative “green” method to the classical chemical dipping with Resorcinol Formaldehyde Latex: plasma treatments are environmentally friendly and easy to use. 2-isoprepenyl-2-oxazoline (2-iox) was employed as precursor and the treatments were performed in a vacuum system, both in a continuous regime and a pulsed regime. Initially, the coatings were deposited on polyethylene terephthalate sheets to study the wettability (by the measurement of contact angle) and the thickness (by profilometer) of the plasma polymer. The chemical characterization was investigated by Infrared and X-ray Photoelectron spectroscopies. Finally, the adhesion of the polyethylene terephthalate sheets was measured by Peel Test, using the coating as adhesive and as a pre-dip. The measurement of the peel force made it possible to optimize the plasma parameters that were applied on the monofilament. The adhesion was estimated by the measure of the extraction force and the evaluation of the coverage compared with those of the classical chemical treatment Resorcinol Formaldehyde Latex. Full article

(This article belongs to the Special Issue Surface Plasma Treatments)

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11 pages, 2048 KiB

Open AccessEditor’s ChoiceArticle

Influence of the Bottom Color Modification and Material Color Modification Process on the Performance of Modified Poplar

by Qingqing Liu, Di Gao and Wei Xu

Coatings 2021, 11(6), 660; https://doi.org/10.3390/coatings11060660 - 31 May 2021

Cited by 38 | Viewed by 3622

Abstract

According to the old surface coating process of European and American furniture, the surface of modified poplar is first differentiated pre-treatment, and then the bottom color modification and material color modification are respectively applied to the modified poplar after the surface differentiation treatment. [...] Read more.

According to the old surface coating process of European and American furniture, the surface of modified poplar is first differentiated pre-treatment, and then the bottom color modification and material color modification are respectively applied to the modified poplar after the surface differentiation treatment. The visual physical quantity and physical and chemical properties were measured and compared with mahogany, which is commonly used in old furniture in Europe and America to explore the effect of colorants and coloring steps, as well as different surface pretreatments on the coloring effect. Finally, it is concluded that continuous coloring operations can narrow the difference in brightness and red color value in the coloring layer of modified poplar and mahogany. Continuous coloring operations increase the difference between the yellow-green color values of modified poplar and mahogany. Therefore, the coloring difference between modified poplar and mahogany was affected by the colorant and coloring steps. Through color accumulation, the gap between the two in the target color coloring effect can be reduced, thereby reducing the difference between the coloring effect of modified poplar and mahogany. Full article

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8 pages, 3121 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

N⁺ Irradiation and Substrate-Induced Variability in the Metamagnetic Phase Transition of FeRh Films

by Steven P. Bennett, Samuel W. LaGasse, Marc Currie, Olaf Van’t Erve, Joseph C. Prestigiacomo, Cory D. Cress and Syed B. Qadri

Coatings 2021, 11(6), 661; https://doi.org/10.3390/coatings11060661 - 31 May 2021

Cited by 5 | Viewed by 4161

Abstract

Metamagnetic FeRh has been the focus of numerous studies for its highly unique antiferromagnetic (AF) to ferromagnetic (FM) metamagnetic transition. While this phase transition usually occurs above room temperature (often T_c > 400 K), both ion irradiation and strained epitaxial growth have [...] Read more.

Metamagnetic FeRh has been the focus of numerous studies for its highly unique antiferromagnetic (AF) to ferromagnetic (FM) metamagnetic transition. While this phase transition usually occurs above room temperature (often T_c > 400 K), both ion irradiation and strained epitaxial growth have been used to bring it to applicable temperatures. Nevertheless, cross sample variability is pervasive in these studies. Here we explore the optical and magnetic properties of 35 nm thick FeRh grown by magnetron sputter deposition simultaneously on two different single crystal substrates: epitaxially on MgO (001) and highly strained with large lattice mismatch on Al₂O₃ (1000). We then irradiate the epitaxial film with 5 keV N⁺ ions to introduce disorder (and to a lesser extent, modify chemical composition) without effecting the surface morphology. We find that the phase-transitional properties of both films are strikingly different due to the large lattice mismatch, despite being grown in tandem with nominally identical growth conditions including Fe/Rh stoichiometry, pressure, and temperature. We observe that N⁺ implantation lowers T_c by ~60 K, yielding a sample with nominally the same transition temperature as the non-epitaxial film on sapphire, yet with a significantly increased magnetic moment, a larger magnetization change and a more abrupt transition profile. We attribute these differences to the Volmer-Weber type growth mode induced by the sapphire substrate and the resulting rougher surface morphology. Full article

(This article belongs to the Special Issue Epitaxial Thin Films: Properties and Applications)

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14 pages, 4052 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Effects of Polysilane Addition to Chlorobenzene and High Temperature Annealing on CH₃NH₃PbI₃ Perovskite Photovoltaic Devices

by Takeo Oku, Masaya Taguchi, Atsushi Suzuki, Kaede Kitagawa, Yugo Asakawa, Satoshi Yoshida, Masanobu Okita, Satoshi Minami, Sakiko Fukunishi and Tomoharu Tachikawa

Coatings 2021, 11(6), 665; https://doi.org/10.3390/coatings11060665 - 31 May 2021

Cited by 35 | Viewed by 4048

Abstract

CH₃NH₃PbI₃ perovskite photovoltaic devices treated with a polysilane layer were fabricated and characterized. Decaphenylcyclopentasilane (DPPS) in chlorobenzene solution was deposited at the surface of the perovskite layer, and the resulting device was annealed at 140–260 °C. The photoconversion [...] Read more.

CH₃NH₃PbI₃ perovskite photovoltaic devices treated with a polysilane layer were fabricated and characterized. Decaphenylcyclopentasilane (DPPS) in chlorobenzene solution was deposited at the surface of the perovskite layer, and the resulting device was annealed at 140–260 °C. The photoconversion efficiencies of the DPPS-treated device remained high even after 255 days in ambient air. Raman scattering spectroscopy and ab initio molecular orbital calculations of DPPS suggested that it increased hole transport efficiency in the treated devices, which was confirmed from the high shunt resistances of the DPPS-treated devices. Full article

(This article belongs to the Special Issue Synthesis, Chracterization and Applications of Coated Composite Materials for Energy Applications)

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18 pages, 34718 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Consolidation and Adhesion of Pictorial Layers on a Stone Substrate. The Study Case of the Virgin with the Child from Palazzo Madama, in Turin

by Anita Negri, Marco Nervo, Stefania Di Marcello and Daniele Castelli

Coatings 2021, 11(6), 624; https://doi.org/10.3390/coatings11060624 - 23 May 2021

Cited by 7 | Viewed by 4273

Abstract

The study and the restoration of a polychrome limestone statue representing the Virgin with the Child, from Palazzo Madama in Turin (NW Italy) offered interesting conservation issue related to the polychromy on stone. To preserve the pictorial layers, it was necessary to re-establish [...] Read more.

The study and the restoration of a polychrome limestone statue representing the Virgin with the Child, from Palazzo Madama in Turin (NW Italy) offered interesting conservation issue related to the polychromy on stone. To preserve the pictorial layers, it was necessary to re-establish the cohesion among the different polychrome layers (original and repainted) and the adhesion between polychrome film and the stone substrate. Particular attention was paid to the choice of intervention materials, selected through a preliminary survey of the scientific literature, and then verified by laboratory tests (tape test, colorimetric test, and permeability test). The most suitable product should to be able to penetrate porosity, to consolidate the layers, to make the pictorial film adhere with the stone surface, and to avoid changes in the colour and in the permeability. The material chosen also had to ensure compatibility with the cleaning method that could only take place after the consolidation of the pictorial layers due to the problematic state of preservation. A range of products, characterised by their small particle size and low viscosity, was tested, and a micro-acrylic resin was selected and successfully applied on the polychromy of the sculpture. Full article

(This article belongs to the Special Issue Conservation Tools, Protocols and Treatments on Painted Surfaces, Metal Leaves and Finishes in Cultural Heritage)

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16 pages, 6577 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Fabrication of Thermal Plasma Sprayed NiTi Coatings Possessing Functional Properties

by Sneha Samal, Ondřej Tyc, Jan Cizek, Jakub Klecka, František Lukáč, Orsolya Molnárová, Esther de Prado, Zdeněk Weiss, Jaromír Kopeček, Luděk Heller, Petr Šittner and Tomáš Chráska

Coatings 2021, 11(5), 610; https://doi.org/10.3390/coatings11050610 - 20 May 2021

Cited by 25 | Viewed by 4594

Abstract

Thick NiTi shape memory alloy coatings (300–500 µm) were produced on graphite and AISI 304 substrates by radio frequency inductively-coupled plasma spray technology (RF-ICP) from feedstock NiTi powders. Their microstructure as well as chemical and phase composition were characterized and a methodology for [...] Read more.

Thick NiTi shape memory alloy coatings (300–500 µm) were produced on graphite and AISI 304 substrates by radio frequency inductively-coupled plasma spray technology (RF-ICP) from feedstock NiTi powders. Their microstructure as well as chemical and phase composition were characterized and a methodology for the characterization of functional shape memory properties of the thick coatings was developed. The coatings exhibited cubic to monoclinic martensitic transformation and shape memory effect. The presented results prove that NiTi coatings with functional thermomechanical properties can be easily produced on structural materials by RF-ICP. Further optimization will be needed to prepare NiTi coatings with better microstructural and chemical homogeneity. Full article

(This article belongs to the Special Issue Thermal Plasma Processing for Coating: Structural, Functional Properties of Thick Films)

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16 pages, 2320 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Pseudo-Planar Organic Heterojunctions by Sequential Printing of Quasi-Miscible Inks

by Ana-Gianina Gereanu, Camillo Sartorio, Aurelio Bonasera, Giuliana Giuliano, Sebastiano Cataldo, Michelangelo Scopelliti, Giuseppe Arrabito and Bruno Pignataro

Coatings 2021, 11(5), 586; https://doi.org/10.3390/coatings11050586 - 17 May 2021

Cited by 5 | Viewed by 3821

Abstract

This work deals with the interfacial mixing mechanism of picoliter (pL)-scale droplets produced by sequential inkjet printing of organic-based inks onto ITO/PET surfaces at a moderately high Weber number (~10¹). Differently from solution dispensing processes at a high Bond number such [...] Read more.

This work deals with the interfacial mixing mechanism of picoliter (pL)-scale droplets produced by sequential inkjet printing of organic-based inks onto ITO/PET surfaces at a moderately high Weber number (~10¹). Differently from solution dispensing processes at a high Bond number such as spin coating, the deposition by inkjet printing is strictly controlled by droplet velocity, ink viscosity, and surface tension. In particular, this study considers the interfacial mixing of droplets containing the most investigated donor/acceptor couple for organic solar cells, i.e., poly(3-hexylthiophene) (P3HT) and (6,6)-phenyl-C₆₁-butyric acid methyl ester (PCBM), showing how low-viscosity and low-surface energy inks can be leveraged for the fabrication of an interface suitable for a pseudo-planar heterojunction (pseudo-PHJ) organic solar cell (OSC) that is a convenient alternative to a bulk heterojunction (BHJ) OSC. The resulting thin-film morphology and molecular organization at the P3HT/PCBM interface are investigated, highlighting the roles of dissolution-driven molecular recirculation. This report represents a first step toward the sequential inkjet printing fabrication of pseudo-PHJ OSCs at low consumption of solvents/chemicals. Full article

(This article belongs to the Special Issue Application of Graphene and Two-Dimensional Materials in Thin Films)

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15 pages, 2753 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Impact of Water-Repellent Products on the Moisture Transport Properties and Mould Susceptibility of External Thermal Insulation Composite Systems

by Renata Roncon, Giovanni Borsoi, João L. Parracha, Inês Flores-Colen, Rosário Veiga and Lina Nunes

Coatings 2021, 11(5), 554; https://doi.org/10.3390/coatings11050554 - 8 May 2021

Cited by 13 | Viewed by 4270

Abstract

External Thermal Insulation Composite Systems (ETICS) are constructive solutions widely used to increase the thermal insulation in new and retrofitted buildings. However, these systems can present several anomalies due to their constant exposure to weathering agents and anthropic factors. Water is generally the [...] Read more.

External Thermal Insulation Composite Systems (ETICS) are constructive solutions widely used to increase the thermal insulation in new and retrofitted buildings. However, these systems can present several anomalies due to their constant exposure to weathering agents and anthropic factors. Water is generally the major cause of degradation. Thus, the application of water-repellent products can minimize the appearance of anomalies and increase the durability of the systems. In this paper, acrylic-based and siloxane-based hydrophobic products were applied to ETICS, with the aim of assessing the compatibility, effectiveness, and durability of these products. The moisture transport properties and mould susceptibility were assessed through laboratory tests on untreated and treated specimens. The durability of the hydrophobic treatments was also evaluated through artificial aging tests (heat-cold and freeze-thaw cycles). Results show that the protection products generally decreased water absorption, slightly decreased the drying rate, and presented adequate water vapor permeability. After aging, the products still had reasonable effectiveness and, with one exception, improved the water vapor diffusion of the systems. Additionally, ETICS underwent an alteration in the finishing coat (possible modification of the porosity) due to the aging cycles. No clear linear correlation was found between the contact angle values and water absorption results, evidencing the influence of other factors related to the composition of the water-repellent products. Full article

(This article belongs to the Special Issue Advanced Coatings for Buildings - Challenges and Opportunities)

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15 pages, 6030 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Hydrogen and Deuterium Incorporation in ZnO Films Grown by Atomic Layer Deposition

by Sami Kinnunen, Manu Lahtinen, Kai Arstila and Timo Sajavaara

Coatings 2021, 11(5), 542; https://doi.org/10.3390/coatings11050542 - 3 May 2021

Cited by 6 | Viewed by 7590

Abstract

Zinc oxide (ZnO) thin films were grown by atomic layer deposition using diethylzinc (DEZ) and water. In addition to depositions with normal water, heavy water (²H₂O) was used in order to study the reaction mechanisms and the hydrogen incorporation [...] Read more.

Zinc oxide (ZnO) thin films were grown by atomic layer deposition using diethylzinc (DEZ) and water. In addition to depositions with normal water, heavy water (²H₂O) was used in order to study the reaction mechanisms and the hydrogen incorporation at different deposition temperatures from 30 to 200 °C. The total hydrogen concentration in the films was found to increase as the deposition temperature decreased. When the deposition temperature decreased close to room temperature, the main source of impurity in hydrogen changed from ¹H to ²H. A sufficiently long purging time changed the main hydrogen isotope incorporated in the film back to ¹H. A multiple short pulse scheme was used to study the transient steric hindrance. In addition, the effect of the storage of the samples in ambient conditions was studied. During the storage, the deuterium concentration decreased while the hydrogen concentration increased an equal amount, indicating that there was an isotope exchange reaction with ambient H₂ and/or H₂O. Full article

(This article belongs to the Special Issue Coatings and Thin Film for Chemical Vapor Deposition (CVD) Application)

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27 pages, 8793 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Development of DLC-Coated Solid SiAlON/TiN Ceramic End Mills for Nickel Alloy Machining: Problems and Prospects

by Sergey N. Grigoriev, Marina A. Volosova, Sergey V. Fedorov, Anna A. Okunkova, Petr M. Pivkin, Pavel Y. Peretyagin and Artem Ershov

Coatings 2021, 11(5), 532; https://doi.org/10.3390/coatings11050532 - 29 Apr 2021

Cited by 79 | Viewed by 6659

Abstract

The study is devoted to the development and testing of technological principles for the manufacture of solid end mills from ceramics based on a powder composition of α-SiAlON, β-SiAlON, and TiN additives, including spark plasma sintering powder composition, diamond sharpening of sintered ceramic [...] Read more.

The study is devoted to the development and testing of technological principles for the manufacture of solid end mills from ceramics based on a powder composition of α-SiAlON, β-SiAlON, and TiN additives, including spark plasma sintering powder composition, diamond sharpening of sintered ceramic blanks for shaping the cutting part of mills and deposition of anti-friction Si-containing diamond-like carbon (DLC) coatings in the final stage. A rational relationship between the components of the powder composition at spark plasma sintering was established. The influence of optimum temperature, which is the most critical sintering parameter, on ceramic samples’ basic physical and mechanical properties was investigated. DLC coatings’ role in changing the surface properties of ceramics based on SiAlON, such as microrelief, friction coefficient, et cetera, was studied. A comparative analysis of the efficiency of two tool options, such as developed samples of experimental mills made of SiAlON/TiN and commercial samples ceramic mills based on SiAlON, doped with stabilizing additives containing Yb when processing nickel alloys (NiCr20TiAl alloy was used as an example). DLC coatings’ contribution to the quantitative indicators of the durability of ceramic mills and the surface quality of machined products made of nickel alloy is shown. Full article

(This article belongs to the Special Issue Technologies of Coatings and Surface Hardening for Tool Industry)

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22 pages, 2819 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Curcumin: Modern Applications for a Versatile Additive

by Florentina Monica Raduly, Valentin Raditoiu, Alina Raditoiu and Violeta Purcar

Coatings 2021, 11(5), 519; https://doi.org/10.3390/coatings11050519 - 28 Apr 2021

Cited by 42 | Viewed by 7565

Abstract

The recent development of several methods for extracting curcumin from the root of the plant Curcuma longa has led to intensified research on the properties of curcumin and its fields of application. Following the studies and the accreditation of curcumin as a natural [...] Read more.

The recent development of several methods for extracting curcumin from the root of the plant Curcuma longa has led to intensified research on the properties of curcumin and its fields of application. Following the studies and the accreditation of curcumin as a natural compound with antifungal, antiviral, and antibacterial properties, new fields of application have been developed in two main directions—food and medical, respectively. This review paper aims to synthesize the fields of application of curcumin as an additive for the prevention of spoilage, safety, and quality of food. Simultaneously, it aims to present curcumin as an additive in products for the prevention of bacterial infections and health care. In both cases, the types of curcumin formulations in the form of (nano)emulsions, (nano)particles, or (nano)composites are presented, depending on the field and conditions of exploitation or their properties to be used. The diversity of composite materials that can be designed, depending on the purpose of use, leaves open the field of research on the conditioning of curcumin. Various biomaterials active from the antibacterial and antibiofilm point of view can be intuited in which curcumin acts as an additive that potentiates the activities of other compounds or has a synergistic activity with them. Full article

(This article belongs to the Special Issue Natural Materials in Functional Coatings)

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15 pages, 14616 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Thermal Atomic Layer Deposition of Yttrium Oxide Films and Their Properties in Anticorrosion and Water Repellent Coating Applications

by Christian Dussarrat, Nicolas Blasco, Wontae Noh, Jooho Lee, Jamie Greer, Takashi Teramoto, Sunao Kamimura, Nicolas Gosset and Takashi Ono

Coatings 2021, 11(5), 497; https://doi.org/10.3390/coatings11050497 - 23 Apr 2021

Cited by 9 | Viewed by 6790

Abstract

The thermal atomic layer deposition (ThALD) of yttrium oxide (Y₂O₃) was developed using the newly designed, liquid precursor, Y(EtCp)₂(ⁱPr₂-amd), as the yttrium source in combination with different oxygen sources, such as ozone, water [...] Read more.

The thermal atomic layer deposition (ThALD) of yttrium oxide (Y₂O₃) was developed using the newly designed, liquid precursor, Y(EtCp)₂(ⁱPr₂-amd), as the yttrium source in combination with different oxygen sources, such as ozone, water and even molecular oxygen. Saturation was observed for the growth of the Y₂O₃ films within an ALD window of 300 to 450 °C and a growth per cycle (GPC) up to 1.1 Å. The resulting Y₂O₃ films possess a smooth and crystalline structure, while avoiding any carbon and nitrogen contamination, as observed by X-ray photoelectron spectroscopy (XPS). The films showed strong resistance to fluorine-containing plasma, outperforming other resistant materials, such as silicon oxide, silicon nitride and alumina. Interestingly, the hydrophilic character exhibited by the film could be switched to hydrophobic after exposure to air, with water contact angles exceeding 90°. After annealing under N₂ flow at 600 °C for 4 min, the hydrophobicity was lost, but proved recoverable after prolonged air exposure or intentional hydrocarbon exposure. The origin of these changes in hydrophobicity was examined. Full article

(This article belongs to the Special Issue Thin and Thick Films: Deposition, Characterization and Applications)

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16 pages, 5413 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

High Transmittance Superhydrophobic Coatings with Durable Self-Cleaning Properties

by Michele Ferrari, Paolo Piccardo, Justine Vernet and Francesca Cirisano

Coatings 2021, 11(5), 493; https://doi.org/10.3390/coatings11050493 - 22 Apr 2021

Cited by 22 | Viewed by 4999

Abstract

One of the most important factors determining a significant reduction in optical devices’ efficiency is the accumulation of soiling substances such as dust, which, especially in solar power plants, implies higher costs and materials ageing. The use of superhydrophobic (SH) coatings, water contact [...] Read more.

One of the most important factors determining a significant reduction in optical devices’ efficiency is the accumulation of soiling substances such as dust, which, especially in solar power plants, implies higher costs and materials ageing. The use of superhydrophobic (SH) coatings, water contact angle (CA) greater than 150°, represents a suitable solution to improve the self-cleaning action while at the same time providing high transmittance for energy conversion. A mixed organic–inorganic SH coating with surface roughness below 100 nm was prepared by an easily scalable spray method and employed, allowing us to modulate the covered area and transparency. The coating has been also investigated while simulating pollution agents like acid rain, harsh environments, and the impact of continuous water droplets and dust particles with different physicochemical properties. The spray coating method allows us to obtain a modulated SH and self-cleaning surface showing CA > 170°, high transmittance in UV-Vis range and the ability to completely restore its initial properties in terms of wettability and transmittance after durability and soiling tests. Full article

(This article belongs to the Section Functional Polymer Coatings and Films)

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32 pages, 6627 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Passive Layers and Corrosion Resistance of Biomedical Ti-6Al-4V and β-Ti Alloys

by Patrizia Bocchetta, Liang-Yu Chen, Juliana Dias Corpa Tardelli, Andréa Cândido dos Reis, Facundo Almeraya-Calderón and Paola Leo

Coatings 2021, 11(5), 487; https://doi.org/10.3390/coatings11050487 - 21 Apr 2021

Cited by 181 | Viewed by 15951

Abstract

The high specific strength, good corrosion resistance, and great biocompatibility make titanium and its alloys the ideal materials for biomedical metallic implants. Ti-6Al-4V alloy is the most employed in practical biomedical applications because of the excellent combination of strength, fracture toughness, and corrosion [...] Read more.

The high specific strength, good corrosion resistance, and great biocompatibility make titanium and its alloys the ideal materials for biomedical metallic implants. Ti-6Al-4V alloy is the most employed in practical biomedical applications because of the excellent combination of strength, fracture toughness, and corrosion resistance. However, recent studies have demonstrated some limits in biocompatibility due to the presence of toxic Al and V. Consequently, scientific literature has reported novel biomedical β-Ti alloys containing biocompatible β-stabilizers (such as Mo, Ta, and Zr) studying the possibility to obtain similar performances to the Ti-6Al-4V alloys. The aim of this review is to highlight the corrosion resistance of the passive layers on biomedical Ti-6Al-4V and β-type Ti alloys in the human body environment by reviewing relevant literature research contributions. The discussion is focused on all those factors that influence the performance of the passive layer at the surface of the alloy subjected to electrochemical corrosion, among which the alloy composition, the method selected to grow the oxide coating, and the physicochemical conditions of the body fluid are the most significant. Full article

(This article belongs to the Special Issue Anodizing Processes for the Production of Advanced Functional Coatings)

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32 pages, 535 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Enhancing Lithium Manganese Oxide Electrochemical Behavior by Doping and Surface Modifications

by Alexandru-Horaţiu Marincaş and Petru Ilea

Coatings 2021, 11(4), 456; https://doi.org/10.3390/coatings11040456 - 15 Apr 2021

Cited by 26 | Viewed by 7664

Abstract

Lithium manganese oxide is regarded as a capable cathode material for lithium-ion batteries, but it suffers from relative low conductivity, manganese dissolution in electrolyte and structural distortion from cubic to tetragonal during elevated temperature tests. This review covers a comprehensive study about the [...] Read more.

Lithium manganese oxide is regarded as a capable cathode material for lithium-ion batteries, but it suffers from relative low conductivity, manganese dissolution in electrolyte and structural distortion from cubic to tetragonal during elevated temperature tests. This review covers a comprehensive study about the main directions taken into consideration to supress the drawbacks of lithium manganese oxide: structure doping and surface modification by coating. Regarding the doping of LiMn₂O₄, several perspectives are studied, which include doping with single or multiple cations, only anions and combined doping with cations and anions. Surface modification approach consists in coating with different materials like carbonaceous compounds, oxides, phosphates and solid electrolyte solutions. The modified lithium manganese oxide performs better than pristine samples, showing improved cyclability, better behaviour at high discharge c-rates and elevated temperate and improves lithium ions diffusion coefficient. Full article

(This article belongs to the Special Issue Electrodeposition of Thin Films for Energy Applications)

13 pages, 2972 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Synthesis and Properties of p-Si/n-Cd_1−xAg_xO Heterostructure for Transparent Photodiode Devices

by Mannarsamy Anitha, Karuppiah Deva Arun Kumar, Paolo Mele, Nagarajan Anitha, Karunamoorthy Saravanakumar, Mahmoud Ahmed Sayed, Atif Mossad Ali and Lourdusamy Amalraj

Coatings 2021, 11(4), 425; https://doi.org/10.3390/coatings11040425 - 7 Apr 2021

Cited by 8 | Viewed by 3368

Abstract

We developed silver-doped Cd₁–_xAg_xO thin films (where x = 0, 0.01, 0.02, 0.03 and 0.04) on amorphous glass substrate by an automated nebulizer spray pyrolysis set-up. The XRD patterns show rock salt cubic crystal structures, and the [...] Read more.

We developed silver-doped Cd₁–_xAg_xO thin films (where x = 0, 0.01, 0.02, 0.03 and 0.04) on amorphous glass substrate by an automated nebulizer spray pyrolysis set-up. The XRD patterns show rock salt cubic crystal structures, and the crystallite sizes vary with respect to Ag doping concentrations. SEM images exhibited a uniform distribution of grains with the addition of Ag; this feature could support the enhancement of electron mobility. The transmittance spectra reveal that all films show high transmittance in the visible region with the observed bandgap of about 2.40 eV. The room temperature photoluminescence (PL) studies show the increase of near-band-edge (NBE) emission of the films prepared by different Ag doping levels, resulting in respective decreases in the bandgaps. The photodiode performance was analyzed for the fabricated p-Si/n-Cd₁–_xAg_xO devices. The responsivity, external quantum efficiency and detectivity of the prepared p-Si/n-Cd₁–_xAg_xO device were investigated. The repeatability of the optimum (3 at.% Ag) photodiode was also studied. The present investigation suggests that Cd₁–_xAg_xO thin films are the potential candidates for various industrial and photodetector applications. Full article

(This article belongs to the Special Issue Functional Oxide Thin Films and Nanostructures: Growth, Properties, and Applications)

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23 pages, 1534 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Natural Ingredients in Functional Coatings—Recent Advances and Future Challenges

by Radu Claudiu Fierascu, Irina Fierascu and Irina Elena Chican

Coatings 2021, 11(4), 429; https://doi.org/10.3390/coatings11040429 - 7 Apr 2021

Cited by 8 | Viewed by 5142

Abstract

In recent decades, coating materials have gained researchers’ interest, finding applications in different areas such as antimicrobial coatings for biomedical applications, coatings for increasing the shelf-life of commercial products, or coatings for the conservation of cultural heritage artifacts. The use of new types [...] Read more.

In recent decades, coating materials have gained researchers’ interest, finding applications in different areas such as antimicrobial coatings for biomedical applications, coatings for increasing the shelf-life of commercial products, or coatings for the conservation of cultural heritage artifacts. The use of new types of coating materials based on natural ingredients can lead to the removal of harmful chemicals and contribute to the development of materials having different and promising properties. New challenges can appear both in the production process, as well as in the case of final application, when coating materials must be applied on various supports. The present review paper aims to be a critical discussion regarding the possibility of using natural ingredients as functional coatings, and to prove that the same material can be used in different fields, from the biomedical to environmental, or from cultural heritage protection to the food and cosmetic industries. The paper is based on the newest published studies, and its main goal is to be an inspiration source for researchers, in order to create more functional and applicable composite coatings in specific fields. Full article

(This article belongs to the Special Issue Natural Materials in Functional Coatings)

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18 pages, 33167 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Improving the Protective Properties of Shellac-Based Varnishes by Functionalized Nanoparticles

by Maduka L. Weththimuni, Chiara Milanese, Maurizio Licchelli and Marco Malagodi

Coatings 2021, 11(4), 419; https://doi.org/10.3390/coatings11040419 - 4 Apr 2021

Cited by 24 | Viewed by 4847

Abstract

Shellac is a natural varnish still known as one of the most elegant finishes for furniture and musical instruments, and currently used for restoration and refinishing of wooden antiques. However, it displays some limitations such as (i) sensitivity to alcoholic solvents (ii) softness [...] Read more.

Shellac is a natural varnish still known as one of the most elegant finishes for furniture and musical instruments, and currently used for restoration and refinishing of wooden antiques. However, it displays some limitations such as (i) sensitivity to alcoholic solvents (ii) softness of the coating, and (iii) considerable weathering due to photo- and bio-degradation. Hence, the main aim of this study was to improve the properties of shellac-based finish by introducing functionalized nanoparticles. Two inorganic nano-sized materials were considered: ZnO that was expected to reduce photo- and bio-degradation problems, and ZrO₂ that was expected to improve the hardness of the varnish. Nanoparticles were synthesized and treated with a bifunctional silane coupling agent. Both plain and functionalized nanoparticles were extensively characterized using different experimental techniques. Functionalized nanoparticles were grafted on shellac through a reaction involving the epoxy-rings introduced on their surface. The resulting modified varnishes were applied on maple wood specimens according to traditional procedures. Different instrumental techniques and testing methods were used to characterize both nano-sized materials and the corresponding nanocomposites, as well as to evaluate the performance of the new coatings. The investigated composite materials display the same aesthetic appearance as plain shellac, while some other properties were improved. In particular, both nanocomposites are distinctly less soluble in alcohols than plain shellac and display antifungal properties. Moreover, coating containing functionalized ZnO nanoparticles displays photo-protection behavior, while shellac modified with ZrO₂ nanoparticles exhibits a higher hardness when compared to the traditional varnish. Full article

(This article belongs to the Special Issue Advanced Coatings for Cultural Heritage Preservation)

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19 pages, 4826 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Surface Chemistry, Crystal Structure, Size and Topography Role in the Albumin Adsorption Process on TiO₂ Anatase Crystallographic Faces and Its 3D-Nanocrystal: A Molecular Dynamics Study

by Giuseppina Raffaini

Coatings 2021, 11(4), 420; https://doi.org/10.3390/coatings11040420 - 4 Apr 2021

Cited by 10 | Viewed by 5348

Abstract

TiO₂ is widely used in biomaterial implants. The topography, chemical and structural properties of titania surfaces are an important aspect to study. The size of TiO₂ nanoparticles synthetized by sol–gel method can influence the responses in the biological environment, and by [...] Read more.

TiO₂ is widely used in biomaterial implants. The topography, chemical and structural properties of titania surfaces are an important aspect to study. The size of TiO₂ nanoparticles synthetized by sol–gel method can influence the responses in the biological environment, and by using appropriate heat treatments different contents of different polymorphs can be formed. Protein adsorption is a crucial step for the biological responses, involving, in particular, albumin, the most abundant blood protein. In this theoretical work, using molecular mechanics and molecular dynamics methods, the adsorption process of an albumin subdomain is reported both onto specific different crystallographic faces of TiO₂ anatase and also on its ideal three-dimensional nanosized crystal, using the simulation protocol proposed in my previous theoretical studies about the adsorption process on hydrophobic ordered graphene-like or hydrophilic amorphous polymeric surfaces. The different surface chemistry of anatase crystalline faces and the nanocrystal topography influence the adsorption process, in particular the interaction strength and protein fragment conformation, then its biological activity. This theoretical study can be a useful tool to better understand how the surface chemistry, crystal structure, size and topography play a key role in protein adsorption process onto anatase surface so widely used as biomaterial. Full article

(This article belongs to the Special Issue Thin Films and Coatings by Sol-Gel Chemistry: Synthesis, Characterization and Applications)

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19 pages, 9272 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Diffusion Aluminide Coatings for Hot Corrosion and Oxidation Protection of Nickel-Based Superalloys: Effect of Fluoride-Based Activator Salts

by Virgilio Genova, Laura Paglia, Giovanni Pulci, Cecilia Bartuli and Francesco Marra

Coatings 2021, 11(4), 412; https://doi.org/10.3390/coatings11040412 - 1 Apr 2021

Cited by 23 | Viewed by 5912

Abstract

The influence of two different fluoride-based activator salts (NH₄F and AlF₃) was studied for diffusion aluminide coatings obtained via pack cementation on a Ni-based superalloy (René 108DS). The resistance to oxidation and hot corrosion was assessed as a function [...] Read more.

The influence of two different fluoride-based activator salts (NH₄F and AlF₃) was studied for diffusion aluminide coatings obtained via pack cementation on a Ni-based superalloy (René 108DS). The resistance to oxidation and hot corrosion was assessed as a function of the concentration of activator salts used during the synthesis process by means of pack cementation. Two different concentrations were selected for activator salts (respecting the equimolarity of fluoride in the synthesis) and the obtained diffusion coatings were compared in terms of morphology, thickness and composition, as well as in terms of microstructural evolution after high temperature exposure. Isothermal oxidation tests were conducted at 1050 °C in air for 100 h in a tubular furnace. The oxidation kinetics were evaluated by measuring the weight variation with exposure time. The microstructural evolution induced by the high temperature exposure was investigated by SEM microscopy, EDS analysis and X-ray diffraction. Results showed that the coatings obtained with AlF₃ activator salt are thicker than those obtained using NH₄F as a consequence of different growth mechanism during pack-cementation. Despite this evidence, it was found that the NH₄F coatings show a better oxidation resistance, both in terms of total mass gain and of quality of the microstructure of the thermally grown oxide. On the other hand, coatings produced with high concentration of AlF₃ exhibited a better resistance in hot corrosion conditions, showing negligible mass variations after 200 h of high temperature exposure to aggressive NaCl and Na₂SO₄ salts. Full article

(This article belongs to the Section Corrosion, Wear and Erosion)

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42 pages, 9689 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Extrusion-Based 3D Printing Applications of PLA Composites: A Review

by Eda Hazal Tümer and Husnu Yildirim Erbil

Coatings 2021, 11(4), 390; https://doi.org/10.3390/coatings11040390 - 29 Mar 2021

Cited by 262 | Viewed by 28965

Abstract

Polylactic acid (PLA) is the most widely used raw material in extrusion-based three-dimensional (3D) printing (fused deposition modeling, FDM approach) in many areas since it is biodegradable and environmentally friendly, however its utilization is limited due to some of its disadvantages such as [...] Read more.

Polylactic acid (PLA) is the most widely used raw material in extrusion-based three-dimensional (3D) printing (fused deposition modeling, FDM approach) in many areas since it is biodegradable and environmentally friendly, however its utilization is limited due to some of its disadvantages such as mechanical weakness, water solubility rate, etc. FDM is a simple and more cost-effective fabrication process compared to other 3D printing techniques. Unfortunately, there are deficiencies of the FDM approach, such as mechanical weakness of the FDM parts compared to the parts produced by the conventional injection and compression molding methods. Preparation of PLA composites with suitable additives is the most useful technique to improve the properties of the 3D-printed PLA parts obtained by the FDM method. In the last decade, newly developed PLA composites find large usage areas both in academic and industrial circles. This review focuses on the chemistry and properties of pure PLA and also the preparation methods of the PLA composites which will be used as a raw material in 3D printers. The main drawbacks of the pure PLA filaments and the necessity for the preparation of PLA composites which will be employed in the FDM-based 3D printing applications is also discussed in the first part. The current methods to obtain PLA composites as raw materials to be used as filaments in the extrusion-based 3D printing are given in the second part. The applications of the novel PLA composites by utilizing the FDM-based 3D printing technology in the fields of biomedical, tissue engineering, human bone repair, antibacterial, bioprinting, electrical conductivity, electromagnetic, sensor, battery, automotive, aviation, four-dimensional (4D) printing, smart textile, environmental, and luminescence applications are presented and critically discussed in the third part of this review. Full article

(This article belongs to the Special Issue Surface Modification for Additive Manufacturing: Materials, Processing, Applications and Future Challenges)

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23 pages, 3256 KiB

Open AccessEditor’s ChoiceReview

Migration of Silver and Copper Nanoparticles from Food Coating

by Hamed Ahari and Leila Khoshboui Lahijani

Coatings 2021, 11(4), 380; https://doi.org/10.3390/coatings11040380 - 26 Mar 2021

Cited by 54 | Viewed by 8287

Abstract

Packaging containing nanoparticles (NPs) can increase the shelf life of products, but the presence of NPs may hazards human life. In this regard, there are reports regarding the side effect and cytotoxicity of nanoparticles. The main aim of this research was to study [...] Read more.

Packaging containing nanoparticles (NPs) can increase the shelf life of products, but the presence of NPs may hazards human life. In this regard, there are reports regarding the side effect and cytotoxicity of nanoparticles. The main aim of this research was to study the migration of silver and copper nanoparticles from the packaging to the food matrix as well as the assessment techniques. The diffusion and migration of nanoparticles can be analyzed by analytical techniques including atomic absorption, inductively coupled plasma mass spectrometry, inductively coupled plasma atomic emission, and inductively coupled plasma optical emission spectroscopy, as well as X-ray diffraction, spectroscopy, migration, and titration. Inductively coupled plasma-based techniques demonstrated the best results. Reports indicated that studies on the migration of Ag/Cu nanoparticles do not agree with each other, but almost all studies agree that the migration of these nanoparticles is higher in acidic environments. There are widespread ambiguities about the mechanism of nanoparticle toxicity, so understanding these nanoparticles and their toxic effects are essential. Nanomaterials that enter the body in a variety of ways can be distributed throughout the body and damage human cells by altering mitochondrial function, producing reactive oxygen, and increasing membrane permeability, leading to toxic effects and chronic disease. Therefore, more research needs to be done on the development of food packaging coatings with consideration given to the main parameters affecting nanoparticles migration. Full article

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15 pages, 1870 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Environmental Impact of Wood Modification

by Callum Hill, Mark Hughes and Daniel Gudsell

Coatings 2021, 11(3), 366; https://doi.org/10.3390/coatings11030366 - 23 Mar 2021

Cited by 25 | Viewed by 5693

Abstract

The modification of wood involves extra processing over and above what is associated with un-modified material and this will involve an associated environmental impact. There is now a body of information on this due to the presence in the public domain of a [...] Read more.

The modification of wood involves extra processing over and above what is associated with un-modified material and this will involve an associated environmental impact. There is now a body of information on this due to the presence in the public domain of a number of environmental product declarations (EPDs). Using these data, it is possible to determine what the extra impact associated with the modification is. The process of modification results in a life extension of the product, which has implications regarding the storage of sequestered atmospheric carbon in the harvested wood products (HWP) materials’ pool and also extended maintenance cycles (e.g., longer periods between applying coatings). Furthermore, the life extension benefits imparted by wood modification need to be compared with the use of other technologies, such as conventional wood preservatives. This paper analysed the published data from a number of sources (peer-reviewed literature, published EPDs, databases) to compare the impacts associated with different modification technologies. The effect of life extension was examined by modelling the carbon flow dynamics of the HWP pool and determining the effect of different life extension scenarios. Finally, the paper examined the impact of different coating periods, and the extensions thereof, imparted by the use of different modified wood substrates. Full article

(This article belongs to the Special Issue Wood Modification: Characterization, Modelling and Applications)

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12 pages, 3554 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Improving the Laser Texture Strategy to Get Superhydrophobic Aluminum Alloy Surfaces

by Annalisa Volpe, Sara Covella, Caterina Gaudiuso and Antonio Ancona

Coatings 2021, 11(3), 369; https://doi.org/10.3390/coatings11030369 - 23 Mar 2021

Cited by 34 | Viewed by 5077

Abstract

Changing the wetting properties of surfaces is attracting great interest in many fields, in particular to achieve a surface with a superhydrophobic behavior. Laser machining is an emerging technique to functionalize materials with high precision and flexibility without any chemical treatment. However, when [...] Read more.

Changing the wetting properties of surfaces is attracting great interest in many fields, in particular to achieve a surface with a superhydrophobic behavior. Laser machining is an emerging technique to functionalize materials with high precision and flexibility without any chemical treatment. However, when it is necessary to treat large area surfaces laser-based methods are still too slow to be exploited in industrial productions. In this work, we show that by improving the laser texture strategy it is possible to reduce the laser processing time to produce superhydrophobic aluminum alloy surfaces. Three different surface texture geometries were micromachined; namely, square, circular and triangular lattice grooves. We found that if the spacing between the grooves is narrow, i.e., when the percentage of the textured surface is high, the volume of air trapped inside the micromachined structures plays an important role in the wetting behavior. Meanwhile, when the groove spacing approaches the droplet dimensions, the texture geometry has a preponderant influence. Based on these findings an appropriate choice of the laser texture strategy allowed the fabrication of superhydrophobic aluminum alloy surfaces with a 10% reduction of processing time. Full article

(This article belongs to the Special Issue Laser Surface Engineering)

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15 pages, 8743 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

The Physical Properties of Submicron and Nano-Grained La_0.7Sr_0.3MnO₃ and Nd_0.7Sr_0.3MnO₃ Synthesised by Sol–Gel and Solid-State Reaction Methods

by Lik Nguong Lau, Kean Pah Lim, Amirah Natasha Ishak, Mohd Mustafa Awang Kechik, Soo Kien Chen, Noor Baa’yah Ibrahim, Muralidhar Miryala, Masato Murakami and Abdul Halim Shaari

Coatings 2021, 11(3), 361; https://doi.org/10.3390/coatings11030361 - 22 Mar 2021

Cited by 20 | Viewed by 4120

Abstract

La_0.7Sr_0.3MnO₃ (LSMO) and Nd_0.7Sr_0.3MnO₃ (NSMO) possess excellent colossal magnetoresistance (CMR). However, research work on the neodymium-based system is limited to date. A comparative study between LSMO and NSMO prepared by sol–gel and solid-state [...] Read more.

La_0.7Sr_0.3MnO₃ (LSMO) and Nd_0.7Sr_0.3MnO₃ (NSMO) possess excellent colossal magnetoresistance (CMR). However, research work on the neodymium-based system is limited to date. A comparative study between LSMO and NSMO prepared by sol–gel and solid-state reaction methods was undertaken to assess their structural, microstructural, magnetic, electrical, and magneto-transport properties. X-ray diffraction and structure refinement showed the formation of a single-phase composition. Sol–gel-synthesised NSMO was revealed to be a sample with single crystallite grains and exhibited intriguing magnetic and electrical transport behaviours. Magnetic characterisation highlighted that Curie temperature (T_C) decreases with the grain size. Strong suppression of the metal–insulator transition temperature (T_MI) was observed and attributed to the magnetically disordered grain surface and distortion of the MnO₆ octahedra. The electrical resistivity in the metallic region was fitted with theoretical models, and the conduction mechanism could be explained by the grain/domain boundary, electron–electron, and electron–magnon scattering process. The increase in the scattering process was ascribed to the morphology changes. Enhancement of low-field magnetoresistance (LFMR) was observed in nano-grained samples. The obtained results show that the grain size and its distribution, as well as the crystallite formation, strongly affect the physical properties of hole-doped manganites. Full article

(This article belongs to the Special Issue New Advance in Superconductor and Superconducting Thin Films)

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12 pages, 2983 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Sputter-Deposited Ag Nanoparticles on Electrospun PCL Scaffolds: Morphology, Wettability and Antibacterial Activity

by Daniele Valerini, Loredana Tammaro, Roberta Vitali, Gloria Guillot and Antonio Rinaldi

Coatings 2021, 11(3), 345; https://doi.org/10.3390/coatings11030345 - 18 Mar 2021

Cited by 30 | Viewed by 4369

Abstract

Porous scaffolds made of biocompatible and environmental-friendly polymer fibers with diameters in the nano/micro range can find applications in a wide variety of sectors, spanning from the biomedical field to textiles and so on. Their development has received a boost in the last [...] Read more.

Porous scaffolds made of biocompatible and environmental-friendly polymer fibers with diameters in the nano/micro range can find applications in a wide variety of sectors, spanning from the biomedical field to textiles and so on. Their development has received a boost in the last decades thanks to advances in the production methods, such as the electrospinning technique. Conferring antimicrobial properties to these fibrous structures is a primary requirement for many of their applications, but the addition of antimicrobial agents by wet methods can present a series of drawbacks. In this work, strong antibacterial action is successfully provided to electrospun polycaprolactone (PCL) scaffolds by silver (Ag) addition through a simple and flexible way, namely the sputtering deposition of silver onto the PCL fibers. SEM-EDS analyses demonstrate that the polymer fibers get coated by Ag nanoparticles without undergoing any alteration of their morphological integrity upon the deposition process. The influence on wettability is evaluated with polar (water) and non-polar (diiodomethane) liquids, evidencing that this coating method allows preserving the hydrophobic character of the PCL polymer. Excellent antibacterial action (reduction > 99.995% in 4 h) is demonstrated against Escherichia coli. The easy fabrication of these PCL-Ag mats can be applicable to the production of biomedical devices, bioremediation and antifouling systems in filtration, personal protective equipment (PPE), food packaging materials, etc. Full article

(This article belongs to the Special Issue Antibacterial Surfaces, Thin Films, and Nanostructured Coatings)

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19 pages, 5846 KiB

Open AccessEditor’s ChoiceArticle

Low-Density Insulation Blocks and Hardboards from Amaranth (Amaranthus cruentus) Stems, a New Perspective for Building Applications

by Philippe Evon, Guyonne de Langalerie, Laurent Labonne, Othmane Merah, Thierry Talou, Stéphane Ballas and Thierry Véronèse

Coatings 2021, 11(3), 349; https://doi.org/10.3390/coatings11030349 - 18 Mar 2021

Cited by 8 | Viewed by 3981

Abstract

Nowadays, amaranth appears as a promising source of squalene of vegetable origin. Amaranth oil is indeed one of the most concentrated vegetable oils in squalene, i.e., up to 6% (w/w). This triterpene is highly appreciated in cosmetology, especially for [...] Read more.

Nowadays, amaranth appears as a promising source of squalene of vegetable origin. Amaranth oil is indeed one of the most concentrated vegetable oils in squalene, i.e., up to 6% (w/w). This triterpene is highly appreciated in cosmetology, especially for the formulation of moisturizing creams. It is almost exclusively extracted from the liver of sharks, causing their overfishing. Thus, providing a squalene of renewable origin is a major challenge for the cosmetic industry. The amaranth plant has thus experienced renewed interest in recent years. In addition to the seeds, a stem is also produced during cultivation. Representing up to 80% (w/w) of the plant aerial part, it is composed of a ligneous fraction, the bark, on its periphery, and a pith in its middle. In this study, a fractionation process was developed to separate bark and pith. These two fractions were then used to produce renewable materials for building applications. On the one hand, the bark was used to produce hardboards, with the deoiled seeds acting as natural binder. Such boards are a viable alternative to commercial wood-based panels. On the other hand, the pith was transformed into cohesive and machinable low-density insulation blocks revealing a low thermal conductivity value. Full article

(This article belongs to the Special Issue Natural Fiber Based Composites)

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13 pages, 4224 KiB

Open AccessEditor’s ChoiceArticle

Polymer-Cement Composites Glazing by Concentrated Solar Energy

by Liana Sanda Baltes, Silvia Patachia, Ozgur Ekincioglu, Hulusi Ozkul, Catalin Croitoru, Corneliu Munteanu, Bogdan Istrate and Mircea Horia Tierean

Coatings 2021, 11(3), 350; https://doi.org/10.3390/coatings11030350 - 18 Mar 2021

Cited by 3 | Viewed by 3835

Abstract

Macro defect free (MDF) cements are polymer-cement composites characterized by high biaxial flexural strength compared to traditional concrete, having as a drawback a low water resistance. Glazing these composite materials with an inorganic enamel containing TiO₂ nano-particles has led to a high [...] Read more.

Macro defect free (MDF) cements are polymer-cement composites characterized by high biaxial flexural strength compared to traditional concrete, having as a drawback a low water resistance. Glazing these composite materials with an inorganic enamel containing TiO₂ nano-particles has led to a high water-stable material with advanced photocatalytic properties. Classic glazing by thermal treatment of samples, at 1050 °C, requires energy consumption and long-time performing. The purpose of this paper is to test the use of solar radiation as a source of energy in the glazing process. A vertical axis solar furnace has been used, from PROMES-CNRS Solar Laboratory, Font-Romeu Odeillo, France, and it has been observed that a uniform appearance of the glaze coating has been achieved; it shows high scratch resistance, meaning a good hardness and adhesion to the substrate. The obtained film was also characterized by SEM, EDS and XRD, aiming to evidence the coat morphology, the TiO₂ distribution and its crystallinity alteration, when compared to the samples obtained by classic thermal treatment. The conclusion of the paper is that using solar radiation in the MDF cement glazing process is a promising approach for obtaining multifunctional materials. Full article

(This article belongs to the Section Plasma Coatings, Surfaces & Interfaces)

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20 pages, 797 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Antifungal Hydroxypropyl Methylcellulose (HPMC)-Lipid Composite Edible Coatings and Modified Atmosphere Packaging (MAP) to Reduce Postharvest Decay and Improve Storability of ‘Mollar De Elche’ Pomegranates

by Bruno Di Millo, Victoria Martínez-Blay, María B. Pérez-Gago, Maricruz Argente-Sanchis, Amparo Grimal, Elena Baraldi and Lluís Palou

Coatings 2021, 11(3), 308; https://doi.org/10.3390/coatings11030308 - 9 Mar 2021

Cited by 14 | Viewed by 4737

Abstract

Pomegranate exhibits important postharvest quality losses that limit its storage potential, caused mainly by weight loss, chilling injury and fungal diseases. In this work, we evaluated the effect of novel hydroxypropyl methylcellulose (HPMC) edible coatings (ECs) formulated with three different lipids (beeswax (BW), [...] Read more.

Pomegranate exhibits important postharvest quality losses that limit its storage potential, caused mainly by weight loss, chilling injury and fungal diseases. In this work, we evaluated the effect of novel hydroxypropyl methylcellulose (HPMC) edible coatings (ECs) formulated with three different lipids (beeswax (BW), carnauba wax, and glycerol monostearate), as hydrophobic components, and two different GRAS salts (potassium bicarbonate (PBC) and sodium benzoate (SB)), as antifungal ingredients, to control weight loss and natural fungal decay of ‘Mollar de Elche’ pomegranates during storage at 20 °C. Afterwards, selected antifungal ECs and commercial modified atmosphere packaging (MAP) films were assayed alone or in combination to control natural decay and preserve fruit quality of pomegranates stored at 5 °C for 4 months plus 1 week at 20 °C. Results showed that ECs amended with SB reduced pomegranate latent infections caused by Botrytis cinerea and wound diseases caused by Penicillium spp. Moreover, MAP technologies were confirmed as an efficient mean to preserve freshness, prevent fruit shriveling and rind browning, and reduce fungal decay, thus extending storage life of pomegranates. The combination HPMC-BW-SB + MAP was the most promising treatment as it reduced weight loss and decay, without negatively affecting the fruit physicochemical and sensory quality. Full article

(This article belongs to the Special Issue Chitosan and Other Edible Coatings with Antimicrobial Activity: Synthesis, Properties and Horticultural Applications II)

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18 pages, 3990 KiB

Open AccessEditor’s ChoiceArticle

Interplay of Hydrophobic Thiol and Polar Epoxy Silicate Groups on Microstructural Development in Low-Alcohol, Crosslinked Sol–Gel Coatings for Corrosion Prevention

by Shegufa Shetranjiwalla, Andrew J. Vreugdenhil and Oliver Strong

Coatings 2021, 11(3), 306; https://doi.org/10.3390/coatings11030306 - 8 Mar 2021

Cited by 8 | Viewed by 3272

Abstract

We have demonstrated that our patented, crosslinked, sol–gel, epoxy–thiol silicates made from the combination of (a) tetraethoxysilane (TEOS, T), 3-glycidoxypropyltrimethoxysilane (GPTMS, G), and the (b) sulfur-containing 3-mercaptopropyltrimethoxysilane (MPTMS, S) with TEOS in a 1:1 stoichiometric ratio form the 1:1 TGST [...] Read more.

We have demonstrated that our patented, crosslinked, sol–gel, epoxy–thiol silicates made from the combination of (a) tetraethoxysilane (TEOS, T), 3-glycidoxypropyltrimethoxysilane (GPTMS, G), and the (b) sulfur-containing 3-mercaptopropyltrimethoxysilane (MPTMS, S) with TEOS in a 1:1 stoichiometric ratio form the 1:1 TGST (crosslinked epoxy and thiol silicates) coating, which can be successfully utilized for the corrosion protection of low-carbon steel. Alcohols that are a by-product of sol–gel reactions influence the network formation, crosslinking density, and formulation stability, are volatile organic contents, and are regulated in the coatings industry. To improve environmental sustainability, a series of low-alcohol (LA) formulations with TG:ST ratios of 3:1 to 1:3 was prepared to investigate the microstructural development and crosslinking reactions emerging from the interplay of the hydrophobic thiol and polar epoxy silicates induced by the low-alcohol environment. The impact on crosslinking density was characterized by Fourier Transform Infrared (FTIR), Raman, XPS, viscosity, and pot-life measurements. Low-alcohol TGST (LA(TGST)) formulations were compared, using the example of 1:1 TGST, to corresponding TGST formulations where alcohols were retained. The reduced impact of LA(TGST) formulations on global warming was quantified. The glossy and scratch-resistant LA(TGST) coatings showed 71% enhanced corrosion protection compared to the non-crosslinked hybrids. Full article

(This article belongs to the Special Issue Organic–Inorganic Hybrid Sol–Gel Materials for Corrosion Mitigation)

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17 pages, 8482 KiB

Open AccessEditor’s ChoiceArticle

Characterization and Identification of Varnishes on Copper Alloys by Means of UV Imaging and FTIR

by Miriam Truffa Giachet, Julie Schröter and Laura Brambilla

Coatings 2021, 11(3), 298; https://doi.org/10.3390/coatings11030298 - 5 Mar 2021

Cited by 9 | Viewed by 3792

Abstract

The application of varnishes on the surface of metal objects has been a very common practice since antiquity, both for protective and aesthetic purposes. One specific case concerns the use of tinted varnishes on copper alloys in order to mimic gilding. This practice, [...] Read more.

The application of varnishes on the surface of metal objects has been a very common practice since antiquity, both for protective and aesthetic purposes. One specific case concerns the use of tinted varnishes on copper alloys in order to mimic gilding. This practice, especially flourishing in the 19th century for scientific instruments, decorative objects, and liturgical items, results in large museum collections of varnished copper alloys that need to be preserved. One of the main challenges for conservators and restorers deals with the identification of the varnishes through non-invasive and affordable analytical techniques. We hereby present the experimental methodology developed in the framework of the LacCA and VERILOR projects at the Haute École ARC of Neuchâtel for the identification of gold varnishes on brass. After extensive documentary research and analytical campaigns on varnished museum objects, various historic shellac-based varnishes were created and applied by different methods on a range of brass substrates with different finishes. The samples were then characterized by UV imaging and infrared spectroscopy before and after artificial ageing. The comparative study of these two techniques was performed for different thicknesses of the same varnish and for different shellac grades in order to implement an identification methodology based on simple non-invasive examination and analytical tools, which are accessible to conservators. Full article

(This article belongs to the Special Issue Conservation Tools, Protocols and Treatments on Painted Surfaces, Metal Leaves and Finishes in Cultural Heritage)

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12 pages, 5790 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Multifunctional Nanocrystalline Cu–Ti Thin Films Enhance Survival and Induce Proliferation of Mouse Fibroblasts In Vitro

by Małgorzata Osękowska, Damian Wojcieszak, Danuta Kaczmarek, Michał Mazur, Agata Obstarczyk and Bogumiła Szponar

Coatings 2021, 11(3), 300; https://doi.org/10.3390/coatings11030300 - 5 Mar 2021

Cited by 3 | Viewed by 3032

Abstract

This paper describes the effect of a nanocrystalline thin film based on copper and titanium on mouse fibroblast cells. Cu–Ti coatings were prepared using magnetron sputtering. In their composition was 25 at.% Cu and 75 at.% Ti. The goal of the study was [...] Read more.

This paper describes the effect of a nanocrystalline thin film based on copper and titanium on mouse fibroblast cells. Cu–Ti coatings were prepared using magnetron sputtering. In their composition was 25 at.% Cu and 75 at.% Ti. The goal of the study was to evaluate the effect of the material on the survival, migration, and proliferative capabilities of mouse L929 fibroblasts. The Cu₂₅Ti₇₅ material had no effect on the induction of cell death and did not disturb the cell cycle phase. The study showed a unique effect of a Cu₂₅Ti₇₅ thin film on mouse fibroblast cells, and the results concerning mitochondrial activity, cell proliferation, and migration proved that the material is nontoxic and shows proliferative properties in a wound healing test. The possible biomedical applications of the new nanocrystalline thin film biomaterial with multifunctional properties are described. Full article

(This article belongs to the Special Issue Biomaterials and Antimicrobial Coatings)

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23 pages, 44474 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Laser Coatings via State-of-the-Art Additive Manufacturing: A Review

by Muhammad Arif Mahmood, Alexandra Bănică, Carmen Ristoscu, Nicu Becherescu and Ion N. Mihăilescu

Coatings 2021, 11(3), 296; https://doi.org/10.3390/coatings11030296 - 4 Mar 2021

Cited by 26 | Viewed by 6322

Abstract

Ceramics and ceramic-reinforced metal matrix composites (CMMCs) demonstrate high wear resistance, excellent chemical inertness, and exceptional properties at elevated temperatures. These characteristics are suitable for their utilization in biomedical, aerospace, electronics, and other high-end engineering industries. The aforementioned performances make them difficult to [...] Read more.

Ceramics and ceramic-reinforced metal matrix composites (CMMCs) demonstrate high wear resistance, excellent chemical inertness, and exceptional properties at elevated temperatures. These characteristics are suitable for their utilization in biomedical, aerospace, electronics, and other high-end engineering industries. The aforementioned performances make them difficult to fabricate via conventional manufacturing methods, requiring high costs and energy consumption. To overcome these issues, laser additive manufacturing (LAM) techniques, with high-power laser beams, were developed and extensively employed for processing ceramics and ceramic-reinforced CMMCs-based coatings. In respect to other LAM processes, laser melting deposition (LMD) excels in several aspects, such as high coating efficiency and lower labor cost. Nevertheless, difficulties such as poor bonding between coating and substrate, cracking, and reduced toughness are still encountered in some LMD coatings. In this article, we review recent developments in the LMD of ceramics and CMMCs-based coatings. Issues and solutions, along with development trends, are discussed and summarized in support of implementing this technology for current industrial use. Full article

(This article belongs to the Collection Pulsed Laser Deposition of Thin Films: Recent Advances and Challenges)

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10 pages, 3325 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Direct-ARPES and STM Investigation of FeSe Thin Film Growth by Nd:YAG Laser

by Sandeep Kumar Chaluvadi, Debashis Mondal, Chiara Bigi, Jun Fujii, Rajdeep Adhikari, Regina Ciancio, Alberta Bonanni, Giancarlo Panaccione, Giorgio Rossi, Ivana Vobornik and Pasquale Orgiani

Coatings 2021, 11(3), 276; https://doi.org/10.3390/coatings11030276 - 26 Feb 2021

Cited by 6 | Viewed by 5477

Abstract

Research on ultrathin quantum materials requires full control of the growth and surface quality of the specimens in order to perform experiments on their atomic structure and electron states leading to ultimate analysis of their intrinsic properties. We report results on epitaxial FeSe [...] Read more.

Research on ultrathin quantum materials requires full control of the growth and surface quality of the specimens in order to perform experiments on their atomic structure and electron states leading to ultimate analysis of their intrinsic properties. We report results on epitaxial FeSe thin films grown by pulsed laser deposition (PLD) on CaF

_{2}

(001) substrates as obtained by exploiting the advantages of an all-in-situ ultra-high vacuum (UHV) laboratory allowing for direct high-resolution surface analysis by scanning tunnelling microscopy (STM), synchrotron radiation X-ray photoelectron spectroscopy (XPS) and angle-resolved photoemission spectroscopy (ARPES) on fresh surfaces. FeSe PLD growth protocols were fine-tuned by optimizing target-to-substrate distance d and ablation frequency, atomically flat terraces with unit-cell step heights are obtained, overcoming the spiral morphology often observed by others. In-situ ARPES with linearly polarized horizontal and vertical radiation shows hole-like and electron-like pockets at the

Γ

and M points of the Fermi surface, consistent with previous observations on cleaved single crystal surfaces. The control achieved in growing quantum materials with volatile elements such as Se by in-situ PLD makes it possible to address the fine analysis of the surfaces by in-situ ARPES and XPS. The study opens wide avenues for the PLD based heterostructures as work-bench for the understanding of proximity-driven effects and for the development of prospective devices based on combinations of quantum materials. Full article

(This article belongs to the Collection Pulsed Laser Deposition of Thin Films: Recent Advances and Challenges)

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13 pages, 2736 KiB

Open AccessEditor’s ChoiceArticle

Improving the Appearance of a 3-Coat-1-Bake Coating Film by Minimizing the Shrinkage Difference between the Three Layers

by Shuji Yomo and Kazuyuki Tachi

Coatings 2021, 11(2), 211; https://doi.org/10.3390/coatings11020211 - 11 Feb 2021

Cited by 1 | Viewed by 3050

Abstract

The 3-coat-1-bake coating system has been widely employed in automobile body painting. This study examined whether the appearance (waviness) of the coating film can be improved by reducing the difference in the shrinkage percentage (by weight) between the primer surfacer and the basecoat [...] Read more.

The 3-coat-1-bake coating system has been widely employed in automobile body painting. This study examined whether the appearance (waviness) of the coating film can be improved by reducing the difference in the shrinkage percentage (by weight) between the primer surfacer and the basecoat and the clearcoat after flow/leveling stops in the clearcoat while baking. To delay the time of flow/leveling stops in the clearcoat (t_C) and to reduce the difference in the shrinkage percentage between the basecoat and clearcoat, solventborne clearcoats were prepared by blocking all or part of the isocyanate group with 3,5-dimethylpyrazole (DMP). t_C was measured using the electric-field tweezers system while baking at 140 °C. The respective shrinkage percentages of the primer surfacer, basecoat, and clearcoat (ω_S, ω_B, and ω_C, respectively) were measured after t_C. t_C increased as the DMP content of the solventborne clearcoat increased. The ω_C value is lower than the ω_S and ω_B values when the DMP content is zero; however, the ω_C value increased when t_C increased, and the ω_S and ω_B values decreased as t_C increased. Wavescan Wa, Wb, Wc, and Wd decreased (i.e., improved the appearance) as |ω_S − ω_B| + |ω_B − ω_C| decreased. We confirmed that reducing the difference in the shrinkage percentage between the primer surfacer, basecoat, and clearcoat after t_C is an effective way to improve the appearance. Full article

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8 pages, 1847 KiB

Open AccessEditor’s ChoiceArticle

Effect of Irradiation with Si⁺ Ions on Phase Transformations in Ti–Al System during Thermal Annealing

by Zhuldyz Sagdoldina, Bauyrzhan Rakhadilov, Sherzod Kurbanbekov, Rauan Kozhanova and Aidar Kengesbekov

Coatings 2021, 11(2), 205; https://doi.org/10.3390/coatings11020205 - 10 Feb 2021

Cited by 9 | Viewed by 2506

Abstract

The article deals with the effect of irradiation with Si+ ions on phase transformations in the Ti–Al system during thermal annealing. An aluminum film with a thickness of 500 nm was deposited on VT1-00 titanium samples by magnetron sputtering, followed by ion implantation. [...] Read more.

The article deals with the effect of irradiation with Si+ ions on phase transformations in the Ti–Al system during thermal annealing. An aluminum film with a thickness of 500 nm was deposited on VT1-00 titanium samples by magnetron sputtering, followed by ion implantation. Samples before and after irradiation with Si ions were annealed in a vacuum of 10⁻⁴ Pa in the temperature range 600–1000 °C. It was established that ion implantation reduces the dissolution of Al in α-Ti with the formation of titanium silicides (TiSi₂, Ti₅Si₃) and stabilizes aluminide phases Ti₃Al rich in aluminum. As a result, a composite structure based on titanium silicide/aluminide was obtained on the surface of the sample synthesized by complex treatment: deposition, irradiation with Si+, and thermal annealing at the near-surface layers. The formation of the phase-structural state of the implanted layers is associated with the displacement of atoms of the crystal lattice, a result that is reflected in an increase in the size of the crystal lattice and a decrease in microdistortion of the lattice. The opposite effect is observed with increasing temperature. This fact is explained by the relaxation of unstable large grains with an excess of internal energies. At the annealing temperature of 900–1000 °C, a significant increase in microhardness was observed due to silicide phases. Full article

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17 pages, 25017 KiB

Open AccessEditor’s ChoiceArticle

Sputter Deposited Metal Layers Embedded in Composites—From Fundamentals to Applications

by Florian Cougnon, Mathias Kersemans, Wim Van Paepegem and Diederik Depla

Coatings 2021, 11(2), 190; https://doi.org/10.3390/coatings11020190 - 6 Feb 2021

Cited by 5 | Viewed by 5026

Abstract

Due to the low heat flux towards the substrate, magnetron sputter deposition offers the possibility to deposit thin films on heat sensitive materials such as fiber-reinforced polymers, also known as composite materials. Passive thermal probe measurements during the sputter deposition of metal layers [...] Read more.

Due to the low heat flux towards the substrate, magnetron sputter deposition offers the possibility to deposit thin films on heat sensitive materials such as fiber-reinforced polymers, also known as composite materials. Passive thermal probe measurements during the sputter deposition of metal layers show indeed that the temperature increase remains well below 25 °C for film thicknesses up to 600 nm. The latter thickness threshold is based on the influence of embedded metal films on the adhesion of the composite plies. Films thicker than this threshold deteriorate the mechanical integrity of the composite. The introduction of the uncured composite in the vacuum chamber strongly affects the base pressure by outgassing of impurities from the composite. The impurities affect the film properties as illustrated by their impact on the Seebeck coefficient of sputter deposited thermocouples. The restrictions to embed thin films in composites, as illustrated by both the heat flux measurements, and the study on the influence of impurities, are however not insurmountable. The possibility to use embedded thin films will be briefly demonstrated in different applications such as digital volume image correlation, thermocouples, and de-icing. Full article

(This article belongs to the Section Thin Films)

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13 pages, 13254 KiB

Open AccessEditor’s ChoiceArticle

Microstructural Charactistics of Plasma Sprayed NiCrBSi Coatings and Their Wear and Corrosion Behaviors

by Songqiang Huang, Jingzhong Zhou, Kuoteng Sun, Hailiang Yang, Weichen Cai, Yi Liu, Ping Zhou, Shuangjie Wu and Hua Li

Coatings 2021, 11(2), 170; https://doi.org/10.3390/coatings11020170 - 31 Jan 2021

Cited by 20 | Viewed by 4220

Abstract

Nickel-based alloys are commonly used as protective coating materials for surface protection applications owing to their superior resistance to corrosion, wear and high-temperature oxidation. It is urgent to study the fundamental mechanism between the structure and corrosion properties of the Nickel-base composite coatings. [...] Read more.

Nickel-based alloys are commonly used as protective coating materials for surface protection applications owing to their superior resistance to corrosion, wear and high-temperature oxidation. It is urgent to study the fundamental mechanism between the structure and corrosion properties of the Nickel-base composite coatings. This paper, therefore, focuses on clarifying the mechanisms of the microstructure influencing the acid corrosion and mechanical characteristics of the as-sprayed NiCrBSi coating and post-heat-treated coating. The formation mechanisms of the amorphous phase of flat particles during the plasma spray process were studied by using X-ray diffraction analysis, Raman spectroscopy and confocal laser scanning microscope at first. Then the evolutionary process of the corrosion structure and phase of the coating in the accelerated corrosion experiment is directly visualized by using scanning electron microscopy and energy spectrum analysis. The mechanical properties of the amorphous NiCrBSi coatings are lastly measured by microhardness and friction wear tests. The critical phenomena and results help to elucidate the relative influence of the surface features of atmospheric plasma sprayed coatings on acid corrosion responses and wear resistance, aiming at contributing to the development of a protective technique for electrical engineering. Full article

(This article belongs to the Special Issue New Advances in Thermal Spraying)

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12 pages, 3097 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Surface Functionalization Utilizing Mesoporous Silica Nanoparticles for Enhanced Evanescent-Field Mid-Infrared Waveguide Gas Sensing

by Diana Al Husseini, Yashaswini Karanth, Junchao Zhou, Daniel Willhelm, Xiaofeng Qian, Ricardo Gutierrez-Osuna, Gerard L. Coté, Pao Tai Lin and Svetlana A. Sukhishvili

Coatings 2021, 11(2), 118; https://doi.org/10.3390/coatings11020118 - 21 Jan 2021

Cited by 12 | Viewed by 4305

Abstract

This work focuses on the development of nanoparticle-based layer-by-layer (LbL) coatings for enhancing the detection sensitivity and selectivity of volatile organic compounds (VOCs) using on-chip mid-infrared (MIR) waveguides (WGs). First, we demonstrate construction of conformal coatings of polymer/mesoporous silica nanoparticles (MSNs) on the [...] Read more.

This work focuses on the development of nanoparticle-based layer-by-layer (LbL) coatings for enhancing the detection sensitivity and selectivity of volatile organic compounds (VOCs) using on-chip mid-infrared (MIR) waveguides (WGs). First, we demonstrate construction of conformal coatings of polymer/mesoporous silica nanoparticles (MSNs) on the surface of Si-based WGs using the LbL technique and evaluate the coating deposition conditions, such as pH and substrate withdrawal speed, on the thickness and homogeneity of the assemblies. We then use the modified WGs to achieve enhanced sensitivity and selectivity of polar organic compounds, such as ethanol, versus non-polar ones, such as methane, in the MIR region. In addition, using density functional theory calculations, we show that such an improvement in sensing performance is achieved due to preferential adsorption of ethanol molecules within MSNs in the vicinity of the WG evanescent field. Full article

(This article belongs to the Special Issue Hybrid Polyelectrolyte Multilayer Films: Fabrication, Properties and Applications)

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15 pages, 3948 KiB

Open AccessEditor’s ChoiceArticle

One-Step Methods to Fabricate Durable Superhydrophobic Coatings for Flexible Electronic Sensors

by Xiang Liu, Kai Chen, Dekun Zhang and Zhiguang Guo

Coatings 2021, 11(1), 95; https://doi.org/10.3390/coatings11010095 - 16 Jan 2021

Cited by 9 | Viewed by 4579

Abstract

Inspired by lotus leaves in nature, superhydrophobic surfaces have attracted extensive attention in many fields. However, their complex preparation process, poor durability and high cost seriously restrict their large-scale application in industrial production. Based on the good flexibility and durability of carbon nanofibers, [...] Read more.

Inspired by lotus leaves in nature, superhydrophobic surfaces have attracted extensive attention in many fields. However, their complex preparation process, poor durability and high cost seriously restrict their large-scale application in industrial production. Based on the good flexibility and durability of carbon nanofibers, several simple modifier-free one-step approaches were adopted to fabricate a durable CNF/PVDF/PDMS conductive superhydrophobic coating. The fabricated coating not only possesses good superhydrophobicity to many kinds of liquids, but also has excellent self-cleaning and anti-fouling properties. In addition, the superhydrophobicity of the obtained multifunctional coating is stable even after harsh bending fatigue deformation, long immersion times and high-temperature treatment. Due to its strong adhesion and excellent conductivity, the CNF/PVDF/PDMS coating displays reliable mechanical stability and superior sensitivity. These distinct features make the obtained conductive superhydrophobic coating a good candidate for multifunctional smart sensors, with great application prospects in gesture detectors, waterproof wearable electronics and health monitors. Full article

(This article belongs to the Section Bioactive Coatings and Biointerfaces)

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24 pages, 6789 KiB

Open AccessEditor’s ChoiceArticle

Surface and Interface Treatments on Wooden Artefacts: Potentialities and Limits of a Non-Invasive Multi-Technique Study

by Claudia Invernizzi, Giacomo Fiocco, Magdalena Iwanicka, Piotr Targowski, Anna Piccirillo, Manuela Vagnini, Maurizio Licchelli, Marco Malagodi and Danilo Bersani

Coatings 2021, 11(1), 29; https://doi.org/10.3390/coatings11010029 - 29 Dec 2020

Cited by 21 | Viewed by 5043

Abstract

Wooden artefacts embrace wide-ranging types of objects, like paintings on panel, sculptures, musical instruments, and furniture. Generally, in the manufacturing process of an artwork, wood is firstly treated with organic and inorganic materials to make it nonporous and morphologically homogeneous, and, at last, [...] Read more.

Wooden artefacts embrace wide-ranging types of objects, like paintings on panel, sculptures, musical instruments, and furniture. Generally, in the manufacturing process of an artwork, wood is firstly treated with organic and inorganic materials to make it nonporous and morphologically homogeneous, and, at last, the surface treatment consists of varnishes or coatings applied with the aims of conferring aesthetic properties and protecting wood from biological growth and external degradation agents, as well as mechanical damage. In this work, different wooden mock-ups were prepared by varying some parameters: concentration of filler and pigment, respectively, in the ground and paint layers, thickness of the protective varnish coat, and sequence of the layers. The mock-ups were subsequently exposed to time-varying artificial aging processes. The multi-analytical non-invasive approach involved spectroscopic (reflection FT-IR, Raman, and X-ray fluorescence), tomographic (optical coherence tomography) and colorimetric techniques. Data were interpreted using both univariate and multivariate methods. The aim was to evaluate potential and limits of each non-invasive technique into the study of different stratigraphies of wooden artworks. This approach was supported by microscopic observations of cross-sections obtained from selected mock-ups. The methodological approach proposed here would add valuable technical know-how and information about the non-invasive techniques applied to the study of wooden artworks. Full article

(This article belongs to the Special Issue Surface and Interface Analysis of Cultural Heritage)

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15 pages, 2156 KiB

Open AccessEditor’s ChoiceArticle

Pulsed Magnetron Sputtering of Strongly Thermochromic VO₂-Based Coatings with a Transition Temperature of 22 °C onto Ultrathin Flexible Glass

by Tomáš Bárta, Jaroslav Vlček, Jiří Houška, Stanislav Haviar, Radomír Čerstvý, Jolanta Szelwicka, Matthias Fahland and John Fahlteich

Coatings 2020, 10(12), 1258; https://doi.org/10.3390/coatings10121258 - 19 Dec 2020

Cited by 15 | Viewed by 4654

Abstract

The reversible semiconductor-to-metal transition of vanadium dioxide (VO₂) makes VO₂-based coatings a promising candidate for thermochromic smart windows, reducing the energy consumption of buildings. This paper deals with maximizing the application potential of these coatings in terms of their [...] Read more.

The reversible semiconductor-to-metal transition of vanadium dioxide (VO₂) makes VO₂-based coatings a promising candidate for thermochromic smart windows, reducing the energy consumption of buildings. This paper deals with maximizing the application potential of these coatings in terms of their performance, an industry-friendly preparation technique, and an industrially relevant substrate. We present a scalable sputter deposition technique for the preparation of strongly thermochromic ZrO₂/V_0.984W_0.016O₂/ZrO₂ coatings on ultrathin flexible glass and standard glass at a relatively low substrate surface temperature (330 °C) and without any substrate bias voltage. The V_0.984W_0.016O₂ layers were deposited by a controlled high-power impulse magnetron sputtering of a V target, combined with a simultaneous pulsed dc magnetron sputtering of a W target. We explain the fundamental principles of this technique using the discharge characteristics measured for both discharges. We characterize the coating structure (X-ray diffraction) and a wide range of optical properties (spectrophotometry and spectroscopic ellipsometry). We find that the coatings combine a transition temperature of 22 °C, a luminous transmittance approaching 50%, a modulation of the solar energy transmittance over 10% and a temperature-independent color. The results in general, and the successful transfer from a standard glass to the ultrathin flexible glass in particular, are crucial for future applications of the coatings on smart windows. Full article

(This article belongs to the Special Issue Magnetron Sputtering Deposition: Challenges, Developments, Perspectives)

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17 pages, 6436 KiB

Open AccessEditor’s ChoiceArticle

Analysis of Surface Roughness and Flank Wear Using the Taguchi Method in Milling of NiTi Shape Memory Alloy with Uncoated Tools

by Emre Altas, Hasan Gokkaya, Meltem Altin Karatas and Dervis Ozkan

Coatings 2020, 10(12), 1259; https://doi.org/10.3390/coatings10121259 - 19 Dec 2020

Cited by 32 | Viewed by 4944

Abstract

The aim of this study was to optimize machining parameters to obtain the smallest average surface roughness (Ra) and flank wear (Vb) values as a result of the surface milling of a nickel-titanium (NiTi) shape memory alloy (SMA) with uncoated cutting tools with [...] Read more.

The aim of this study was to optimize machining parameters to obtain the smallest average surface roughness (Ra) and flank wear (Vb) values as a result of the surface milling of a nickel-titanium (NiTi) shape memory alloy (SMA) with uncoated cutting tools with different nose radius (r_ε) under dry cutting conditions. Tungsten carbide cutting tools with different r_ε (0.4 mm and 0.8 mm) were used in milling operations. The milling process was performed as lateral/surface cutting at three different cutting speeds (V_c) (20, 35 and 50 m/min), feed rates (f_z) (0.03, 0.07 and 0.14 mm/tooth) and a constant axial cutting depth (0.7 mm). The effects of machining parameters in milling experiments were investigated based on the Taguchi L18 (2¹ × 3²) orthogonal sequence, and the data obtained were analyzed using the Minitab 17 software. To determine the effects of processing parameters on Ra and Vb, analysis of variance (ANOVA) was used. The analysis results reveal that the dominant factor affecting the Ra is the cutting tool r_ε, while the main factor affecting Vb is the f_z. Since the predicted values and measured values are very close to each other, it can be said that optimization is correct according to the validation test results. Full article

(This article belongs to the Special Issue Advanced Coating Materials for Machining Processes)

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13 pages, 5138 KiB

Open AccessEditor’s ChoiceArticle

Ag Functionalization of Al-Doped ZnO Nanostructured Coatings on PLA Substrate for Antibacterial Applications

by Daniele Valerini, Loredana Tammaro, Giovanni Vigliotta, Enrica Picariello, Francesco Banfi, Emanuele Cavaliere, Luca Ciambriello and Luca Gavioli

Coatings 2020, 10(12), 1238; https://doi.org/10.3390/coatings10121238 - 17 Dec 2020

Cited by 26 | Viewed by 3761

Abstract

Developing smart, environmentally friendly, and effective antibacterial surfaces is fundamental to contrast the diffusion of human infections and diseases for applications in the biomedical and food packaging sectors. To this purpose, here we combine aluminum-doped zinc oxide (AZO) and Ag to grow nanostructured [...] Read more.

Developing smart, environmentally friendly, and effective antibacterial surfaces is fundamental to contrast the diffusion of human infections and diseases for applications in the biomedical and food packaging sectors. To this purpose, here we combine aluminum-doped zinc oxide (AZO) and Ag to grow nanostructured composite coatings on bioplastic polylactide (PLA) substrates. The AZO layers are grown by RF magnetron sputtering, and then functionalized with Ag in atomic form by RF magnetron sputtering and in form of nanoparticles by supersonic cluster beam deposition. We compare the morphology, wettability, and antimicrobial performance of the nanostructured coatings obtained by the two methods. The different growth modes in the two techniques used for Ag functionalization are found to produce some differences in the surface morphology, which, however, do not induce significant differences in the wettability and antimicrobial response of the coatings. The antibacterial activity is investigated against Escherichia coli and Staphylococcus aureus as representatives of Gram-negative and Gram-positive bacteria, respectively. A preferential antimicrobial action of Ag on the first species and of AZO on the second one is evidenced. Through their combination, we obtain a hybrid composite coating taking advantage of the synergistic dual action of the two materials deposited, with a total bacterial suppression within few minutes for the first species and few hours for the second one, thus representing a valuable solution as a wide-spectrum bactericidal device. Full article

(This article belongs to the Special Issue Antibacterial Surfaces, Thin Films, and Nanostructured Coatings)

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11 pages, 2479 KiB

Open AccessEditor’s ChoiceArticle

Distribution of Characteristic Times: A High-Resolution Spectrum Approach for Visualizing Chemical Relaxation and Resolving Kinetic Parameters of Ionic-Electronic Conducting Ceramic Oxides

by Fuyao Yan, Yiheng Wang, Ying Yang, Lei Zhu, Hui Hu, Zhuofu Tang, Yanxiang Zhang, Mufu Yan, Changrong Xia and Yueming Xu

Coatings 2020, 10(12), 1240; https://doi.org/10.3390/coatings10121240 - 17 Dec 2020

Cited by 5 | Viewed by 3162

Abstract

Surface exchange coefficient (k) and bulk diffusion coefficient (D) are important properties to evaluate the performance of mixed ionic-electronic conducting (MIEC) ceramic oxides for use in energy conversion devices, such as solid oxide fuel cells. The values of k [...] Read more.

Surface exchange coefficient (k) and bulk diffusion coefficient (D) are important properties to evaluate the performance of mixed ionic-electronic conducting (MIEC) ceramic oxides for use in energy conversion devices, such as solid oxide fuel cells. The values of k and D are usually estimated by a non-linear curve fitting procedure based on electrical conductivity relaxation (ECR) measurement. However, the rate-limiting mechanism (or the availability of k and D) and the experimental imperfections (such as flush delay for gaseous composition change, τ_f) are not reflected explicitly in the time–domain ECR data, and the accuracy of k and D demands a careful sensitivity analysis of the fitting error. Here, the distribution of characteristic times (DCT) converted from time–domain ECR data is proposed to overcome the above challenges. It is demonstrated that, from the DCT spectrum, the rate-limiting mechanism and the effect of τ_f are easily recognized, and the values of k, D and τ_f can be determined conjunctly. A strong robustness of determination of k and D is verified using noise-containing ECR data. The DCT spectrum opens up a way towards visible and credible determination of kinetic parameters of MIEC ceramic oxides. Full article

(This article belongs to the Special Issue Surface Engineering of C/N/O Functionalized Materials)

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10 pages, 3980 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Strong Coupling between Tamm and Surface Plasmons for Advanced Optical Bio-Sensing

by Zigmas Balevičius

Coatings 2020, 10(12), 1187; https://doi.org/10.3390/coatings10121187 - 5 Dec 2020

Cited by 27 | Viewed by 4660

Abstract

The total internal reflection ellipsometry method was used to analyse the angular spectra of the hybrid Tamm and surface plasmon modes and to compare their results with those obtained using the conventional single SPR method. As such type of measurement is quite common [...] Read more.

The total internal reflection ellipsometry method was used to analyse the angular spectra of the hybrid Tamm and surface plasmon modes and to compare their results with those obtained using the conventional single SPR method. As such type of measurement is quite common in commercial SPR devices, more detailed attention was paid to the analysis of the p-polarization reflection intensity dependence. The conducted study showed that the presence of strong coupling in the hybrid plasmonic modes increases the sensitivity of the plasmonic-based sensors due to the reduced losses in the metal layer. The experimental results and analysis of the optical responses of three different plasmonic-based samples indicated that the optimized Tamm plasmons

Δ R_{p (T P)}

and optimized surface plasmons

Δ R_{p (S P)}

samples produce a response that is about five and six times greater than the conventional surface plasmon resonance

Δ R_{p (S P R)}

in angular spectra. The sensitivity of the refractive index unit of the spectroscopic measurements for the optimized Tamm plasmon samples was 1.5 times higher than for conventional SPR, while for wavelength scanning, the SPR overcame the optimized TP by 1.5 times. Full article

(This article belongs to the Special Issue Thin Films and Surface Optics)

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