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Coatings, Volume 10, Issue 3 (March 2020) – 108 articles

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Cover Story (view full-size image) The preservation of prehistoric cave paintings in the Magura cave (Bulgaria) is a very challenging [...] Read more.
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Open AccessFeature PaperArticle
Metallurgical Soldering of Duplex CrN Coating in Contact with Aluminum Alloy
Coatings 2020, 10(3), 303; https://doi.org/10.3390/coatings10030303 - 24 Mar 2020
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Abstract
Coatings deposited by physical vapor deposition (PVD) significantly reduce the wear of high pressure die casting tools; however, cast alloy soldering still has a strong negative effect on production efficiency. Although a lot of research has been already done in this field, the [...] Read more.
Coatings deposited by physical vapor deposition (PVD) significantly reduce the wear of high pressure die casting tools; however, cast alloy soldering still has a strong negative effect on production efficiency. Although a lot of research has been already done in this field, the fundamental understanding of aluminum alloy soldering toward PVD coatings is still scarce. Therefore, in this work the performance of CrN duplex coatings with different roughness is evaluated by a modified ejection test performed with delayed (DS) and conventional casting solidification (CS). After the ejection tests, sample surfaces and layers were subjected to comprehensive characterizations of their morphological and chemical characteristics. Considerably lower values of the ejection force were recorded in DS experiments than in CS experiments. Surface roughness played an important role in the CS experiments, while samples with different surface topographies in the DS experiments performed in a similar fashion. The decrease in the ejection force, observed in DS tests, is attributed to the formation of a thick Cr–O layer on CrN coating which reduced soldering and sliding friction against thick Al–O casting scale. The Cr–O layer formed in DS experiments suffered from diffusion wear by cast alloy. The observed oxidation phenomena of nitride coatings may be utilized in a design of non-sticking coatings. Full article
(This article belongs to the Special Issue Surface Topography Effects on Functional Properties of PVD Coatings)
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Open AccessCommunication
Formulation of Lipoprotein Microencapsulated Beadlets by Ionic Complexes in Algae-Based Carbohydrates
Coatings 2020, 10(3), 302; https://doi.org/10.3390/coatings10030302 - 24 Mar 2020
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Abstract
The present study aims to produce sustained-release algae-based carbohydrate microbeadlets of lipoproteins rich-in carotenoids extracted from organic sea buckthorn fruits. β-carotene represented the major compound of the lipoproteins extracts. Emulsification and algae-based carbohydrates, such as sodium-alginate and kappa-carrageenan, provide an inert environment, allowing [...] Read more.
The present study aims to produce sustained-release algae-based carbohydrate microbeadlets of lipoproteins rich-in carotenoids extracted from organic sea buckthorn fruits. β-carotene represented the major compound of the lipoproteins extracts. Emulsification and algae-based carbohydrates, such as sodium-alginate and kappa-carrageenan, provide an inert environment, allowing the embedded targeted bioactive compounds—lipoproteins rich in carotenoids in our case—to maintain greater biological activity and to have a better shelf life. Furthermore, the microbeadlets prepared from sodium-alginate–kappa-carrageenan (0.75%:0.75% w/v) crosslinked with calcium ions showing 90% encapsulation efficiency have been utilized in HPMC capsules using beadlets-in-a-capsule technology, to use as a delivery system for the finished product. The GI simulated tests performed under laboratory conditions suggested that the sodium-alginate–kappa–carrageenan combination could be useful for the formulation-controlled release of microbeadlets containing lipoproteins rich in carotenoids. Full article
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Open AccessArticle
Multilayer Nanoimprinting to Create Hierarchical Stamp Masters for Nanoimprinting of Optical Micro- and Nanostructures
Coatings 2020, 10(3), 301; https://doi.org/10.3390/coatings10030301 - 24 Mar 2020
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Abstract
Nanoimprinting is a well-established replication technology for optical elements, with the capability to replicate highly complex micro- and nanostructures. One of the main challenges, however, is the generation of the master structures necessary for stamp fabrication. We used UV-based Nanoimprint Lithography to prepare [...] Read more.
Nanoimprinting is a well-established replication technology for optical elements, with the capability to replicate highly complex micro- and nanostructures. One of the main challenges, however, is the generation of the master structures necessary for stamp fabrication. We used UV-based Nanoimprint Lithography to prepare hierarchical master structures. To realize structures with two different length scales, conventional nanoimprinting of larger structures and conformal reversal nanoimprinting to print smaller structures on top of the larger structures was performed. Liquid transfer imprint lithography proved to be well suited for this purpose. We used the sample prepared in such a way as a master for further nanoimprinting, where the hierarchical structures can then be imprinted in one single nanoimprinting step. As an example, we presented a diffusor structure with a diffraction-grating structure on top. Full article
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Open AccessArticle
Microstructures and Wear Resistance of FeCoCrNi-Mo High Entropy Alloy/Diamond Composite Coatings by High Speed Laser Cladding
Coatings 2020, 10(3), 300; https://doi.org/10.3390/coatings10030300 - 24 Mar 2020
Viewed by 270
Abstract
FeCoCrNi-Mo high entropy alloy/diamond composite coatings were successfully prepared by high speed laser cladding. A high scanning speed was adopted (>30 mm/s), and the effects of laser power, scanning speed, and diamond content on the microstructure and wear resistance of the composite coating [...] Read more.
FeCoCrNi-Mo high entropy alloy/diamond composite coatings were successfully prepared by high speed laser cladding. A high scanning speed was adopted (>30 mm/s), and the effects of laser power, scanning speed, and diamond content on the microstructure and wear resistance of the composite coating were studied. The processing parameters of laser cladding had significant influence on the dilution ratio, graphitization of diamond, and wear resistance of the composite coatings. When the laser cladding parameters were 3000 W of laser power and the high scanning speed of 50 mm/s, the composite coating exhibited a uniform microstructure, the lowest dilution ratio, and the best wear resistance. The wear resistance of the composite coating was enhanced with the addition of diamond, but microcracks also increased. When the amount of diamond was 15 wt.%, the best combination of microstructures and wear resistance was obtained. Full article
(This article belongs to the Special Issue Surface Treatment by Laser-Assisted Techniques)
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Open AccessFeature PaperArticle
Electron-Beam Domain Patterning in Sr0.61Ba0.39Nb2O6 Crystals
Coatings 2020, 10(3), 299; https://doi.org/10.3390/coatings10030299 - 23 Mar 2020
Viewed by 303
Abstract
The characteristics of electron-beam domain writing (EBDW) on the polar and nonpolar surfaces of the field-cooled (FC) and zero-field cooled (ZFC) Sr0.61Ba0.39Nb2O6 (SBN) crystals are presented in the range of accelerating voltage U from 10 to [...] Read more.
The characteristics of electron-beam domain writing (EBDW) on the polar and nonpolar surfaces of the field-cooled (FC) and zero-field cooled (ZFC) Sr0.61Ba0.39Nb2O6 (SBN) crystals are presented in the range of accelerating voltage U from 10 to 25 kV. The exposure characteristics of the domain diameter d and length Ld (when writing on the polar and nonpolar surfaces, respectively) were measured. With increasing exposure time, d tends to a saturation value, whereas Ld grows linearly, the frontal velocity Vf being of 40 μm/s. At U = 25 kV the achieved d and Ld are of 7 and 40 µm, respectively. The observed peculiar features of EBDW—specifically the domain widening with exposure times and the effect of the polarization state of the crystal on the domain stability—are accounted for by the relaxor features inherent to this material. The effects of electron-beam (EB) irradiation on the local hysteresis loops is evidence of a domain fixation. Full article
(This article belongs to the Special Issue Ferroelectric Thin Films and Devices)
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Open AccessArticle
Effect of Addition of Mo or V on the Structure and Cutting Performance of AlCrN-Based Coatings
Coatings 2020, 10(3), 298; https://doi.org/10.3390/coatings10030298 - 23 Mar 2020
Viewed by 289
Abstract
This study focuses on a comparative analysis of AlCrXN (X = Mo or V) coatings with the reference AlCrN coating via arc ion plating technique (AIP). The XRD and XPS results showed that the AlCrXN coatings were mainly composed of fcc-(Cr,Al)N solid solution [...] Read more.
This study focuses on a comparative analysis of AlCrXN (X = Mo or V) coatings with the reference AlCrN coating via arc ion plating technique (AIP). The XRD and XPS results showed that the AlCrXN coatings were mainly composed of fcc-(Cr,Al)N solid solution phases. Both the AlCrMoN and AlCrVN coatings exhibited much higher hardness and adhesive strength than the AlCrN coating. The addition of Mo or V decreased the coefficient of friction (COF) and wear rate, which was due to the formation of lubricant oxides containing Mo or V on the coating surfaces. The cutting results showed that abrasive wear, adhesive wear, and oxidation wear were the main wear mechanisms for the coated tools at the cutting speeds of 60 m/min and 94 m/min. The addition of Mo or V dramatically improved the cutting performance of AlCrXN-coated tools by increasing the anti-wear ability due to the high hardness and the formed lubricant VOx or MoOx films. Full article
(This article belongs to the Section Corrosion, Wear and Erosion)
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Open AccessArticle
Investigation on Stranski–Krastanow (SK) Growth Mode of Ag Coating in Cu/Ag Core-Shell Composites
Coatings 2020, 10(3), 297; https://doi.org/10.3390/coatings10030297 - 23 Mar 2020
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Abstract
Cu/Ag core-shell composite was synthesized by the replacement-reduction method and was applied to the catalytic field. The specimens were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscope (TEM). The growth mechanism was investigated by the first-principles calculation, including [...] Read more.
Cu/Ag core-shell composite was synthesized by the replacement-reduction method and was applied to the catalytic field. The specimens were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscope (TEM). The growth mechanism was investigated by the first-principles calculation, including the density of states, Mulliken population, and electronic structures. By comparing the calculation and characterization, it is concluded that the difference in interfacial properties leads to the growth of silver on the copper surface in the Stranski–Krastanow (SK) mode. Full article
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Open AccessArticle
Flame-Retardant Wood Composites Based on Immobilizing with Chitosan/Sodium Phytate/Nano-TiO2-ZnO Coatings via Layer-by-Layer Self-Assembly
Coatings 2020, 10(3), 296; https://doi.org/10.3390/coatings10030296 - 22 Mar 2020
Viewed by 284
Abstract
Composite coatings of inorganic nanomaterials with polyelectrolytes are promising materials for wood modification. Endowing wood with flame retardancy behavior can not only broaden the range of applications of wood, but also improve the safety of wood products. In this work, chitosan/sodium phytate/TiO2 [...] Read more.
Composite coatings of inorganic nanomaterials with polyelectrolytes are promising materials for wood modification. Endowing wood with flame retardancy behavior can not only broaden the range of applications of wood, but also improve the safety of wood products. In this work, chitosan/sodium phytate/TiO2-ZnO nanoparticle (CH/SP/nano-TiO2-ZnO) composite coatings were coated on wood surface through layer-by-layer self-assembly. The morphology and chemical composition of the modified wood samples were analyzed using scanning electron microscopy and energy dispersive spectrometry. The thermal degradation properties and flame retardancy of the samples treated with different assembly structures were observed by thermogravimetric analysis, limiting oxygen test, and combustion test. Due to the presence of an effective intumescent flame retardant system and a physical barrier, the CH/SP/nano-TiO2-ZnO coatings exhibited the best flame retardant performance and required only approximately six seconds for self-extinguishing. The coated samples had a limiting oxygen index of 8.4% greater than the original wood. Full article
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Open AccessFeature PaperArticle
Phytochemical Compounds as Cleaning Agents on Granite Colonized by Phototrophic Subaerial Biofilms
Coatings 2020, 10(3), 295; https://doi.org/10.3390/coatings10030295 - 22 Mar 2020
Viewed by 311
Abstract
The society has become increasingly interested in using natural products over chemicals for cleaning activities. In this study, the cleaning potential of formulations embedded in a hydrogel matrix and composed respectively of essential oils (EOs) of Origanum vulgare, Thymus vulgaris, and [...] Read more.
The society has become increasingly interested in using natural products over chemicals for cleaning activities. In this study, the cleaning potential of formulations embedded in a hydrogel matrix and composed respectively of essential oils (EOs) of Origanum vulgare, Thymus vulgaris, and Calamintha nepeta, and their respective main active components (EO-ACs), viz., Carvacrol, Thymol, and Pulegone, on a phototropic biofilm growing on granite was investigated. In addition, and for comparative purposes, analysis with the combination of the three EOs, the combination of the three EO-ACs, and Preventol RI-80® (one of the most effective commercial cleaning agents based on quaternary ammonium salts) in all three cases embedded in a hydrogel matrix, as well as only the hydrogel matrix, distilled water, and Preventol RI-80®, in both latter cases applied with brush, were also studied. The cleaning effect of the treatments was assessed immediately after the treatment and after one and two weeks by color spectrophotometry, a reliable tool to evaluate the presence and vitality of the phototrophs and the cleaning effectiveness in granite. C. nepeta and its active component Pulegone proved to be the most effective and yielded similar results, comparable to those of uncolonized granite, and better than those obtained with Preventol RI-80® applied with brush (most common way), especially at the end of the experiment. These promising first results support the suitable use of the phytochemical compounds used on phototrophs field where there are still few published studies and encourage further investigation toward the evaluation of their exhibited biocidal activity. Full article
(This article belongs to the Special Issue Coatings on Built Heritage and New Build)
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Open AccessFeature PaperArticle
Effect of Electrode Covering Composition on the Microstructure, Wear, and Economic Feasibility of Fe-C-Cr Manual Arc-Welded Hardfacings
Coatings 2020, 10(3), 294; https://doi.org/10.3390/coatings10030294 - 21 Mar 2020
Viewed by 372
Abstract
Manual arc-welded hardfacings are widely used for the protection of new or the restoration of worn parts in agriculture, forestry, and mining applications. A study was conducted to investigate the effect of electrode covering composition on the microstructure, wear (low, average stress abrasion; [...] Read more.
Manual arc-welded hardfacings are widely used for the protection of new or the restoration of worn parts in agriculture, forestry, and mining applications. A study was conducted to investigate the effect of electrode covering composition on the microstructure, wear (low, average stress abrasion; erosion at 30, 50, and 80 m s−1), and economic feasibility of Fe–C–Cr manual arc-welded hardfacings. Hardfacings were produced with the carbon and chrome contents varied in the ranges of 0.87–2.95 and 1.3–33.2 wt.%, respectively. The major phases composing the microstructures of the hardfacings were austenite, perlite, ledeburite, and various carbides, including eutectic M7C3. Technical and economic analyses were performed to assess the economic feasibility of hardfacings and reference wear-resistant steel Hardox 400. A wear and economic feasibility map was created to specify various types and facilitate the selection of optimal hardfacings for specific conditions. The produced Fe–C–Cr coatings were the most effective in low-stress abrasive conditions (up to 7.8 times greater than Hardox 400) and quite effective in erosive conditions (up to 2.9 times greater than Hardox 400). Full article
(This article belongs to the Special Issue Manufacturing and Surface Engineering II)
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Open AccessArticle
Low Frictional MoS2/WS2/FineLPN Hybrid Layers on Nodular Iron
Coatings 2020, 10(3), 293; https://doi.org/10.3390/coatings10030293 - 21 Mar 2020
Viewed by 424
Abstract
The paper presents the new concept of low frictional hybrid composite coatings on nodular cast iron. The structure of it is multilayer and consists of MoS2 and/or WS2 nanoinclusions embedded in the iron nitrides’ zone and relatively deep hard diffusion zone. [...] Read more.
The paper presents the new concept of low frictional hybrid composite coatings on nodular cast iron. The structure of it is multilayer and consists of MoS2 and/or WS2 nanoinclusions embedded in the iron nitrides’ zone and relatively deep hard diffusion zone. It offers a low friction coefficient as well as high wear resistance of coated parts. The details of technology as well as the mechanism of layer’s growth have been presented and discussed. The presented technology may be an interesting alternative for chromium-based galvanic coatings of piston rings made of nodular iron using Cr6+. Full article
(This article belongs to the Special Issue Functional Ceramic Coatings)
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Open AccessCorrection
Correction: Wen et al. Fabrication of Dense Gadolinia-Doped Ceria Coatings via Very-Low-Pressure Plasma Spray and Plasma Spray–Physical Vapor Deposition Process. Coatings 2019, 9, 717
Coatings 2020, 10(3), 292; https://doi.org/10.3390/coatings10030292 - 20 Mar 2020
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Abstract
The author wishes to make the following correction to this paper [...] Full article
Open AccessArticle
Improved Thermal Processing of Polylactic Acid/Oxidized Starch Composites and Flame-Retardant Behavior of Intumescent Non-Wovens
Coatings 2020, 10(3), 291; https://doi.org/10.3390/coatings10030291 - 20 Mar 2020
Viewed by 295
Abstract
Thermoplastic processing and spinning of native starch is very challenging due to (a) the linear and branched polymers (amylose and amylopectin) present in its structure and (b) the presence of inter-and-intramolecular hydrogen bond linkages in its macromolecules that restrict the molecular chain mobility. [...] Read more.
Thermoplastic processing and spinning of native starch is very challenging due to (a) the linear and branched polymers (amylose and amylopectin) present in its structure and (b) the presence of inter-and-intramolecular hydrogen bond linkages in its macromolecules that restrict the molecular chain mobility. Therefore, in this study, oxidized starch (OS) (obtained after oxidation of native starch with sodium perborate) was melt-blended with polylactic acid (PLA) polymer to prepare PLA/OS blends that were then mixed together with ammonium polyphosphate (APP), a halogen-free flame retardant (FR) used as acid donor in intumescent formulations on twin-screw extruder to prepare PLA/OS/APP composites. OS with different concentrations also served as bio-based carbonic source in intumescent formulations. PLA/OS/APP composites were melt spun to multifilament fibers on pilot scale melt-spinning machine and their crystallinity and mechanical properties were optimized by varying spinning parameters. The crystallinity of the fibers was studied by differential scanning calorimetry and thermal stabilities were analyzed by thermogravimetric analysis. Scanning electron microscopy was used to investigate the surface morphology and dispersion of the additives in the fibers. Needle-punched non-woven fabrics from as prepared melt-spun PLA/OS/APP fibers were developed and their fire properties such as heat release rate, total heat release, time to ignition, residual mass % etc. by cone calorimetry test were measured. It was found that PLA/OS/APP composites can be melt spun to multifilament fibers and non-woven flame-retardant fabrics produced thereof can be used in industrial FR applications. Full article
(This article belongs to the Special Issue Flame Retardant Coatings for Plastics and Textiles)
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Open AccessArticle
Hard Quasicrystalline Coatings Deposited by HVOF Thermal Spray to Reduce Ice Accretion in Aero-Structures Components
Coatings 2020, 10(3), 290; https://doi.org/10.3390/coatings10030290 - 20 Mar 2020
Viewed by 340
Abstract
Weather hazards, in particular icing conditions, are an important contributing factor in aviation accidents and incidents worldwide. Many different anti-icing strategies are currently being explored to find suitable long-lasting solutions, such as surface engineering, which can contribute to reduce ice accumulation. Quasicrystals (QCs) [...] Read more.
Weather hazards, in particular icing conditions, are an important contributing factor in aviation accidents and incidents worldwide. Many different anti-icing strategies are currently being explored to find suitable long-lasting solutions, such as surface engineering, which can contribute to reduce ice accumulation. Quasicrystals (QCs) are metallic materials, but with similar properties to those of ceramic materials, such as low thermal and electrical conductivities, and high hardness. In particular, QCs that have low surface energy are commercially used as coatings to replace polytetrafluoroethylene (PTFE), also known as Teflon, on frying pans, as they do not scratch easily. PTFE exhibits excellent anti-wetting and anti-icing properties and therefore QCs appear as good candidates to be employed as ice-phobic coatings. Al-based QCs have been applied by High Velocity Oxyfuel (HVOF) thermal spray on typically used aeronautic materials, such as Ti and Al alloys, as well as steels. The coatings have been characterized and evaluated, including the measurement of hardness, roughness, wetting properties, ice accretion behavior in an icing wind tunnel (IWT), and ice adhesion by a double lap shear test. The coatings were studied, both as-deposited, as well as after grinding, in order to study the effect of the surface roughness and morphology on the ice accretion and adhesion properties. The QC coating was compared with PTFE and two polyurethane (PU)-based commercial paints, one of them known to have anti-icing properties, and the results indicate an ice accretion reduction relative to these two materials, and ice adhesion lower than bare AA6061-T6, or the PU paint in the ground version of one of the two QCs. Since the QC coatings are hard (GPa Vickers hardness > 5), a durable behavior is expected. Full article
(This article belongs to the Special Issue Anti-Icing Coatings and Surfaces)
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Open AccessFeature PaperArticle
Molecular Dynamics Simulations of DNA Adsorption on Graphene Oxide and Reduced Graphene Oxide-PEG-NH2 in the Presence of Mg2+ and Cl ions
Coatings 2020, 10(3), 289; https://doi.org/10.3390/coatings10030289 - 20 Mar 2020
Viewed by 315
Abstract
Graphene and its functionalised derivatives are transforming the development of biosensors that are capable of detecting nucleic acid hybridization. Using a Molecular Dynamics (MD) approach, we explored single-stranded or double-stranded deoxyribose nucleic acid (ssDNA or dsDNA) adsorption on two graphenic species: graphene oxide [...] Read more.
Graphene and its functionalised derivatives are transforming the development of biosensors that are capable of detecting nucleic acid hybridization. Using a Molecular Dynamics (MD) approach, we explored single-stranded or double-stranded deoxyribose nucleic acid (ssDNA or dsDNA) adsorption on two graphenic species: graphene oxide (GO) and reduced graphene oxide functionalized with aminated polyethylene glycol (rGO-PEG-NH2). Innovatively, we included chloride (Cl) and magnesium (Mg2+) ions that influenced both the ssDNA and dsDNA adsorption on GO and rGO-PEG-NH2 surfaces. Unlike Cl, divalent Mg2+ ions formed bridges between the GO surface and DNA molecules, promoting adsorption through electrostatic interactions. For rGO-PEG-NH2, the Mg2+ ions were repulsed from the graphenic surface. The subsequent ssDNA adsorption, mainly influenced by electrostatic forces and hydrogen bonds, could be supported by π–π stacking interactions that were absent in the case of dsDNA. We provide a novel insight for guiding biosensor development. Full article
(This article belongs to the Special Issue Advances in Polymer/Graphene Composite for Bio-Applications)
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Open AccessArticle
SERS Activity of Silver Nanosphere, Triangular Nanoplates, Hexagonal Nanoplates and Quasi-Spherical Nanoparticles: Effect of Shape and Morphology
Coatings 2020, 10(3), 288; https://doi.org/10.3390/coatings10030288 - 20 Mar 2020
Viewed by 301
Abstract
In this work, we prepared different morphologies of silver nanoparticles: nanosphere, triangular nanoplates, hexagonal nanoplates, and quasi-spherical shapes, through one-step synthesis. Hydrogen peroxide was used as the oxidizing agent during the reduction of silver nitrate by sodium borohydride, in the presence of tri-sodium [...] Read more.
In this work, we prepared different morphologies of silver nanoparticles: nanosphere, triangular nanoplates, hexagonal nanoplates, and quasi-spherical shapes, through one-step synthesis. Hydrogen peroxide was used as the oxidizing agent during the reduction of silver nitrate by sodium borohydride, in the presence of tri-sodium citrate and poly-vinyl-pyrrolidone. The obtained silver nanoparticles were fully characterized by UV-Vis spectroscopy, Dynamic Light Scattering and Scanning Electron Microscopy, and successfully used as Surface Enhanced Raman Scattering (SERS) substrates. The effect of shape and morphology on the Raman scattering enhancement was evaluated by using methylene blue as target molecules. The Raman measurements demonstrated that the prepared substrates are reliable and sensitive with analytical enhancement factors, estimated to be around 105 with a concentration of methylene blue 1 μM. When triangular and hexagonal nanoplates were tested with different concentrations of analyte, they demonstrated a good linearity in Raman intensity with a good detection of methylene blue 0.1 μM. Full article
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Open AccessFeature PaperArticle
XPS and FTIR Studies of DC Reactive Magnetron Sputtered TiO2 Thin Films on Natural Based-Cellulose Fibers
Coatings 2020, 10(3), 287; https://doi.org/10.3390/coatings10030287 - 20 Mar 2020
Viewed by 298
Abstract
Natural based-cellulosic fibers are trending due to the global awareness regarding environmental health and because their properties make them a great alternative to the synthetic fibers. However, these fibers also have some hindrances that can be solved with their functionalization. The present study [...] Read more.
Natural based-cellulosic fibers are trending due to the global awareness regarding environmental health and because their properties make them a great alternative to the synthetic fibers. However, these fibers also have some hindrances that can be solved with their functionalization. The present study concerns modification of the surface of natural based-cellulosic fibers extracted from stems of the ginger lily plant (Hedychium gardnerianum) with TiO2 films deposited by DC magnetron sputtering using a titanium (Ti) target. A detailed characterization of the TiO2-coated fibers was investigated by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The results revealed that the sputtered TiO2 films can be attached to the ginger lily fibers mainly by their OH groups. XPS analysis further shows that C–OH group is not dominant, which means that no pure cellulose is present at the surface. Full article
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Open AccessFeature PaperArticle
Composite Ferroelectric Coatings Based on a Heat-Resistant Polybenzoxazole Polymer Matrix
Coatings 2020, 10(3), 286; https://doi.org/10.3390/coatings10030286 - 19 Mar 2020
Viewed by 344
Abstract
The polycondensation of 5,5-methylene bis(2-aminophenol) and the mixture of diamines 5,5-methylene bis(2-aminophenol) and 4,4-(hexafluoroisopropylidene)dianiline (molar ratio 0.8:0.2) with isophthaloyl dichloride was used to synthesize a new heat resistant binder of the composites for microelectronics: poly(o-hydroxyamide) (POA) and poly(amido-o-hydroxy amide) [...] Read more.
The polycondensation of 5,5-methylene bis(2-aminophenol) and the mixture of diamines 5,5-methylene bis(2-aminophenol) and 4,4-(hexafluoroisopropylidene)dianiline (molar ratio 0.8:0.2) with isophthaloyl dichloride was used to synthesize a new heat resistant binder of the composites for microelectronics: poly(o-hydroxyamide) (POA) and poly(amido-o-hydroxy amide) (POA-F). The thermal stability of synthesized polymer coatings, as well as based on them photosensitive compositions with a naphthoquinondiazide photosensitive component were studied in the temperature range from 100 to 500 °C. Ferroelectric composites with nanodispersed lead titanate zirconate powder filler were formed based on these polymer matrices. By manipulating the conditions of the polymer formation, we obtained matrices with different stiffnesses, which reflected on the properties of the composite. The electrophysical parameters of the synthesized polymer and ferroelectric composite coatings were measured in the frequency range from 0.1 Hz to 1.5 GHz and the temperature range from 0 to 300 °C. The frequency and temperature stability of the dielectric constant of ferroelectric composite coatings up to 10 MHz and 300 °C, respectively, are noted. The influence of the composition and structure of the polymer matrix and the grain/matrix interfaces on the thermal stability of the dielectric parameters of composite films is estimated. The shift of the phase transition region toward higher temperatures in the composite structure, as well as the sufficient rigidity of the poly(benzoxazole) matrix, provide high temperature and frequency stability of the dielectric constant of the studied composites. Full article
(This article belongs to the Special Issue Ferroelectric Thin Films and Devices)
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Open AccessArticle
Electrospun Bilayer PAN/Chitosan Nanofiber Membranes Incorporated with Metal Oxide Nanoparticles for Heavy Metal Ion Adsorption
Coatings 2020, 10(3), 285; https://doi.org/10.3390/coatings10030285 - 19 Mar 2020
Viewed by 331
Abstract
Bilayer nanofiber membranes with enhanced adsorption and mechanical properties were produced by combining a layer of polyacrylonitrile (PAN) functionalized with metal oxides (MO) of ZnO or TiO2 with a layer of chitosan (CS) via consecutive electrospinning. The adsorption properties of the bilayer [...] Read more.
Bilayer nanofiber membranes with enhanced adsorption and mechanical properties were produced by combining a layer of polyacrylonitrile (PAN) functionalized with metal oxides (MO) of ZnO or TiO2 with a layer of chitosan (CS) via consecutive electrospinning. The adsorption properties of the bilayer PAN/MO–CS nanofiber membranes against lead (Pb(II)) and cadmium (Cd(II)) ions were investigated, including the effects of the solution pH, initial ion concentrations, and interaction time. The integration of a CS layer into PAN/MO nanofibers increased the adsorption capacity of lead by 102% and cadmium by 405%, compared to PAN/MO single layer. The nonlinear optimization method showed that the pseudo-second-order kinetic model and Langmuir isotherm equation better described the adsorption results. More importantly, the incorporation of a supportive CS nanofiber layer enhanced the tensile strength of PAN/MO–CS bilayer by approximately 68% compared to the PAN/MO single layer, owing to the strong interaction between the fibers at the interface of the two layers. Full article
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Open AccessArticle
Trap State and Charge Recombination in Nanocrystalline Passivized Conductive and Photoelectrode Interface of Dye-Sensitized Solar Cell
Coatings 2020, 10(3), 284; https://doi.org/10.3390/coatings10030284 - 19 Mar 2020
Viewed by 291
Abstract
The dynamic competition between electron generation and recombination was found to be a bottleneck restricting the development of high-performance dye-sensitized solar cells (DSSCs). Introducing a passivation layer on the surface of the TiO2 photoelectrode material plays a crucial role in separating the [...] Read more.
The dynamic competition between electron generation and recombination was found to be a bottleneck restricting the development of high-performance dye-sensitized solar cells (DSSCs). Introducing a passivation layer on the surface of the TiO2 photoelectrode material plays a crucial role in separating the charge by preventing the recombination of photogenerated electrons with the oxidized species. This study aims to understand in detail the kinetics of the electron recombination process of a DSSC fabricated with a conductive substrate and photoelectrode film, both passivized with a layer of nanocrystalline TiO2. Interestingly, the coating, which acted as a passivation layer, suppressed the back-electron transfer and improved the overall performance of the integrated DSSC. The passivation layer reduced the exposed site of the fluorine-doped tin oxide (FTO)–electrolyte interface, thereby reducing the dark current phenomenon. In addition, the presence of the passivation layer reduced the rate of electron recombination related to the surface state recombination, as well as the trapping/de-trapping phenomenon. The photovoltaic properties of the nanocrystalline-coated DSSC, such as short-circuit current, open-circuit voltage, and fill factor, showed significant improvement compared to the un-coated photoelectrode film. The overall performance efficiency improved by about 22% compared to the un-coated photoelectrode-based DSSC. Full article
(This article belongs to the Special Issue Coatings for Solar Cell Applications)
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Open AccessArticle
Novel Synthesis of Core-Shell Biomaterials from Polymeric Filaments with a Bioceramic Coating for Biomedical Applications
Coatings 2020, 10(3), 283; https://doi.org/10.3390/coatings10030283 - 18 Mar 2020
Viewed by 332
Abstract
Bone tissue engineering is constantly in need of new material development with improved biocompatibility or mechanical features closer to those of natural bone. Other important factors are the sustainability, cost, and origin of the natural precursors involved in the technological process. This study [...] Read more.
Bone tissue engineering is constantly in need of new material development with improved biocompatibility or mechanical features closer to those of natural bone. Other important factors are the sustainability, cost, and origin of the natural precursors involved in the technological process. This study focused on two widely used polymers in tissue engineering, namely polylactic acid (PLA) and thermoplastic polyurethane (TPU), as well as bovine-bone-derived hydroxyapatite (HA) for the manufacturing of core-shell structures. In order to embed the ceramic particles on the polymeric filaments surface, the materials were introduced in an electrical oven at various temperatures and exposure times and under various pressing forces. The obtained core-shell structures were characterized in terms of morphology and composition, and a pull-out test was used to demonstrate the particles adhesion on the polymeric filaments structure. Thermal properties (modulated temperature and exposure time) and the pressing force’s influence upon HA particles’ insertion degree were evaluated. More to the point, the form variation factor and the mass variation led to the optimal technological parameters for the synthesis of core-shell materials for prospect additive manufacturing and regenerative medicine applications. Full article
(This article belongs to the Special Issue Recent Advances in Nanostructured Polymer and Inorganic Coatings)
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Open AccessArticle
Zirconium-Aluminum-Oxide Dielectric Layer with High Dielectric and Relatively Low Leakage Prepared by Spin-Coating and the Application in Thin-Film Transistor
Coatings 2020, 10(3), 282; https://doi.org/10.3390/coatings10030282 - 18 Mar 2020
Viewed by 328
Abstract
In this paper, zirconium–aluminum–oxide (ZAO) dielectric layers were prepared by a solution method with intent to combine the high dielectric constant with a low leakage current density. As a result, dielectric layers with improved electrical properties as expected can be obtained by spin-coating [...] Read more.
In this paper, zirconium–aluminum–oxide (ZAO) dielectric layers were prepared by a solution method with intent to combine the high dielectric constant with a low leakage current density. As a result, dielectric layers with improved electrical properties as expected can be obtained by spin-coating the mixed precursor. The chemical and physical properties of the films were measured by thermogravimetric differential scanning calorimetry (TG-DSC), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and a UV spectrometer. It is observed that the oxygen defects and the hydroxide in the films are reduced with the addition of high-bond-energy zirconia, while the films can remain large optical bond gaps thanks to the presence of alumina. The metal-insulator-metal (MIM) devices were fabricated, and it was seen that with a molar ratio of Zr:Al = 3:1 and an annealing temperature of 500 °C, the dielectric layer afforded the highest dielectric constant of 21.1, as well as a relatively low leakage current of 2.5 106 A/cm2@1MV/cm. Furthermore, the indium–gallium–zinc oxide thin-film transistors (IGZO-TFTs) with an optimal ZAO dielectric layer were prepared by the solution method and a mobility of 14.89 cm2/Vs, and a threshold voltage swing of 0.11 V/dec and a 6.1 106 on/off ratio were achieved at an annealing temperature of 500 °C. Full article
(This article belongs to the Special Issue Thin Films for Electronic Applications)
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Open AccessFeature PaperArticle
Insight into the Release Agents/PVD Coatings Interaction for Plastic Mold Technology
Coatings 2020, 10(3), 281; https://doi.org/10.3390/coatings10030281 - 18 Mar 2020
Viewed by 360
Abstract
In polymer processing, the formation of undesired fouling hinders the plastic manufacturing processes. Hence, the use of emulsions as releasing agents is mandatory and their affinity to the mold substrates plays a crucial role. Therefore, this research work has been focused on the [...] Read more.
In polymer processing, the formation of undesired fouling hinders the plastic manufacturing processes. Hence, the use of emulsions as releasing agents is mandatory and their affinity to the mold substrates plays a crucial role. Therefore, this research work has been focused on the wetting properties of commercial water-based release agents (namely Marbocote® W2140, EP, EV-333) towards different Physical Vapor Deposition (PVD) nitride coatings (AlTiN, NbN, ZrN and TiN), usually adopted in the industrial manufacture of Hydrogenated Nitrile Butadiene Rubber (HNBR). The investigated solid substrates were characterized by means of profilometry, SEM/EDX and Surface Free Energy (SFE) analyses, whereas, tensiometric determinations were acquired on the commercial pure and diluted emulsions. The release agents/mold substrates wettability features were studied by means of the work of adhesion and the spreading coefficient. Finally, nitride-coated mold seals were directly tested in an industrial plant with the most performing release agent in terms of adhesive features; for the first time, a deep correlation between the service life, in terms of number of molded seals, and surface (contact angles, work of adhesion and spreading coefficient)/electrochemical (OCP) features was drawn. Full article
(This article belongs to the Special Issue Physical Vapor Deposition)
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Open AccessArticle
Development of Polylactic Acid Films with Selenium Microparticles and Its Application for Food Packaging
Coatings 2020, 10(3), 280; https://doi.org/10.3390/coatings10030280 - 18 Mar 2020
Viewed by 307
Abstract
Selenium is a natural element which exists in the human body and plays an important role in metabolism. Along with this, selenium also possesses antibacterial and antioxidant properties. Using selenium microparticles (SeMPs) in food packaging films is exceptional. In this experiment, a solution [...] Read more.
Selenium is a natural element which exists in the human body and plays an important role in metabolism. Along with this, selenium also possesses antibacterial and antioxidant properties. Using selenium microparticles (SeMPs) in food packaging films is exceptional. In this experiment, a solution casting method was used to make film. For this purpose, we used polylactic acid (PLA) as a substrate for the formation of a film membrane while SeMPs were added with certain ratios to attain antibacterial and antioxidant properties. The effects of SeMPs on the PLA film and the value of SeMPs in food packaging film production were investigated. The effects of the SeMPs contents on the features of the film, such as its mechanical property, solubility, swelling capacity, water vapor permeability, antioxidant activity, and the antibacterial activity of the composite membrane against Staphylococcus aureus (Gram-positive) and Escherichia coli (Gram-negative) strains, were studied. The results manifest that the PLA/SeMPs films showed higher water resistance, UV resistance, antioxidant activity, and antibacterial activity than pure PLA film. When the concentration of SeMPs was 1.5 wt%, the composite membrane showed the best comprehensive performance. Although the tensile strength and elongation at break of the membrane were slightly reduced by the addition of SeMPs, the results show that PLA/SeMPs films are still suitable for food packaging and would be a very promising material for food packaging. Full article
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Open AccessFeature PaperArticle
Cytotoxicity and Mineralization Potential of Four Calcium Silicate-Based Cements on Human Gingiva-Derived Stem Cells
Coatings 2020, 10(3), 279; https://doi.org/10.3390/coatings10030279 - 18 Mar 2020
Viewed by 363
Abstract
The aim of this study was to evaluate the cytotoxicity and mineralization potential of four calcium silicate-based cements on human gingiva-derived stem cells (GDSCs). The materials evaluated in the present study were ProRoot MTA (Dentsply Tulsa Dental Specialties), Biodentine (Septodont), Endocem Zr (Maruchi), [...] Read more.
The aim of this study was to evaluate the cytotoxicity and mineralization potential of four calcium silicate-based cements on human gingiva-derived stem cells (GDSCs). The materials evaluated in the present study were ProRoot MTA (Dentsply Tulsa Dental Specialties), Biodentine (Septodont), Endocem Zr (Maruchi), and RetroMTA (BioMTA). Experimental disks of 6 mm in diameter and 3 mm in height were produced and placed in a 100% humidified atmosphere for 48 h to set. We evaluated the cytotoxic effects of the cements using methyl-thiazoldiphenyl-tetrazolium (MTT) and live/dead staining assays. We used a scratch wound healing assay to evaluate cell migratory ability. Mineralization potential was determined with an Alizarin red S (ARS) staining assay. In the MTT assay, no significant differences were found among the ProRoot MTA, Biodentine, and control groups during the test period (p > 0.05). The Endocem Zr and RetroMTA groups showed relatively lower cell viability than the control group at day 7 (p < 0.05). In the wound healing assay, no significant differences were found among the ProRoot MTA, Biodentine, Endocem Zr, and control groups during the test period (p > 0.05). The RetroMTA group had slower cell migration compared to the control group at days 3 and 4 (p < 0.05). In the ARS assay, the ProRoot MTA, Biodentine, and RetroMTA groups exhibited a significant increase in the formation of mineralized nodules compared to the Endocem Zr and control groups on day 21 (p < 0.05). In conclusion, the four calcium silicate-based cements evaluated in the present study exhibited good biological properties on GDSCs. ProRoot MTA, Biodentine, and RetroMTA showed higher mineralization potential than the Endocem Zr and control groups. Full article
(This article belongs to the Special Issue Recent Advances in Coatings of Implant and Dental Biomaterials)
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Open AccessArticle
TCAD Simulation of the Doping-Less TFET with Ge/SiGe/Si Hetero-Junction and Hetero-Gate Dielectric for the Enhancement of Device Performance
Coatings 2020, 10(3), 278; https://doi.org/10.3390/coatings10030278 - 17 Mar 2020
Viewed by 320
Abstract
The device structure of DLTFET is optimized by the Silvaco TCAD software to solve the problems of lower on-state current and larger miller capacitance of traditional doping-less tunneling field effect transistors (DLTFETs), and the performance can be greatly improved. Different from the traditional [...] Read more.
The device structure of DLTFET is optimized by the Silvaco TCAD software to solve the problems of lower on-state current and larger miller capacitance of traditional doping-less tunneling field effect transistors (DLTFETs), and the performance can be greatly improved. Different from the traditional DLTFETs, the source region and pocket region of the doping-less TFET with the Ge/SiGe/Si hetero-junction and hetero-gate dielectric (H-DLTFET), respectively, use the narrow band-gap semiconductor Ge and SiGe materials, and the channel and drain region both use the silicon material. The H-DLTFET device use the Ge/SiGe hetero-junction engineering to decrease the tunneling barrier width, increase the band-to-band tunneling current, and obtain the higher current switching ratio and ultra-low sub-threshold swing (SS). Besides, the gate dielectric under auxiliary gate uses the low-k dielectric SiO2 material, which can effectively reduce the miller capacitance and improve the capacitance and frequency characteristics. The on-state current, switching ratio, trans-conductance, output current, and output conductance values of H-DLTFET can be increased by two, two, one, one, and one order of magnitude when compared with the DLTFET, respectively. Meanwhile, the point SS and average SS, respectively, decrease from 13 mV/Dec and 31.6 mV/Dec to 5 mV/Dec and 14.3 mV/Dec, and the gate-drain capacitance decrease from 0.99 fF/μm to 0.1 fF/μm. Besides, the cutoff frequency and gain bandwidth product of H-DLTFET are much larger than that of DLTFET, which can be explained by the excellent DC characteristics. The above simulation results show that the H-DLTFET has the better frequency characteristics, so it is more suitable for applications of ultra-low-power integrated circuits. Full article
(This article belongs to the Section Plasma Coatings, Surfaces & Interfaces)
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Open AccessArticle
Organometallic Coatings for Electroluminescence Applications
Coatings 2020, 10(3), 277; https://doi.org/10.3390/coatings10030277 - 17 Mar 2020
Viewed by 333
Abstract
Organometallic compounds embedded in thin films are widely used for Organic Light-Emitting Diodes (OLED), but their functionalities are strongly correlated with the intrinsic properties of those films. Controlling the concentration of the organometallics in the active layers influences the OLED performances through the [...] Read more.
Organometallic compounds embedded in thin films are widely used for Organic Light-Emitting Diodes (OLED), but their functionalities are strongly correlated with the intrinsic properties of those films. Controlling the concentration of the organometallics in the active layers influences the OLED performances through the aggregation processes. These aggregations could lead to crystallization processes that significantly modify the efficiency of light emission in the case of electroluminescent devices. For functional devices with organometallic-based thin films, some improvements, such as the optimization of the charge injection, are needed to increase the light output. One dual emitter IrQ(ppy)2 organometallic compound was chosen for the aggregation correlations from a multitude of macromolecular organometallics that exist on the market for OLED applications. The choice of additional layers like conductive polymers or small molecules as host for the active layer may significantly influence the performances of the OLED based on the IrQ(ppy)2 organometallic compound. The use of the CBP small molecule layer may lead to an increase in the electroluminescence versus the applied voltage. Full article
(This article belongs to the Special Issue Thin Film Coatings for Multifunctional Applications)
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Open AccessArticle
Study on Microstructure and Tribological Performance of Diamond/Cu Composite Coating via Supersonic Laser Deposition
Coatings 2020, 10(3), 276; https://doi.org/10.3390/coatings10030276 - 17 Mar 2020
Viewed by 390
Abstract
The supersonic laser deposition (SLD) of diamond/Cu composite powder is studied over a range of laser power. The deposition efficiency, coating microstructure, cohesive/adhesive bonding, phase composition, micro-hardness, and tribological property of the diamond/Cu composite coating are investigated. The results indicate that, as laser [...] Read more.
The supersonic laser deposition (SLD) of diamond/Cu composite powder is studied over a range of laser power. The deposition efficiency, coating microstructure, cohesive/adhesive bonding, phase composition, micro-hardness, and tribological property of the diamond/Cu composite coating are investigated. The results indicate that, as laser power is increased, deposition efficiency initially increases and then declines. The diamond particles distribute uniformly in the composite coating. Due to the increase of velocity ratio and total energy by laser irradiation, the cohesive/adhesive bonding of the composite coating is improved. The composite coating can preserve the phase composition of the origin powders due to the relatively low heat input during the SLD process. Slight oxidation of the Cu powder can be detected in the coatings prepared with high laser power, which has adverse effects on material deposition. The SLD-diamond/Cu composite coating has superior wear-resistance because of low friction coefficient, high micro-hardness, and uniformly distributed diamond particles. Full article
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Open AccessArticle
WC-Co and WC-Co-Cr Coatings for the Protection of API Pipeline Steel from Corrosion in 4% NaCl Solution
Coatings 2020, 10(3), 275; https://doi.org/10.3390/coatings10030275 - 16 Mar 2020
Viewed by 395
Abstract
Two inorganic coatings, namely 88%WC-12%Co (PSC1) and 86%WC-10%Co-4%Cr (PSC2), were deposited on the surface of an API-2H pipeline steel using high velocity oxy-fuel deposition. The corrosion of the uncoated and coated API-2H steel after their immersion in a solution of 4.0% NaCl for [...] Read more.
Two inorganic coatings, namely 88%WC-12%Co (PSC1) and 86%WC-10%Co-4%Cr (PSC2), were deposited on the surface of an API-2H pipeline steel using high velocity oxy-fuel deposition. The corrosion of the uncoated and coated API-2H steel after their immersion in a solution of 4.0% NaCl for 1 h, 24 h, and 48 h has been studied. Various electrochemical measurements such cyclic potentiodynamic polarization, electrochemical impedance spectroscopy, and potentiostatic current versus time were employed. The surface morphology and analysis were carried out via the use of scanning electron microscopy and energy dispersive X-ray examinations. All experiments have revealed that the deposited coatings decreased the cathodic current, anodic current, corrosion current density (jCorr), absolute current versus time, and the corrosion rate (RCorr) compared to the uncoated API-2H steel. The value of jCorr decreased from 47 µA/cm2 for uncoated steel to 38 µA/cm2 for the PSC1-coated steel and 29 µA/cm2 for the PSC2-coated steel. Moreover, prolonging the time of exposure decreases the jCorr and RCorr values. The jCorr values obtained after 48 h recorded 32, 26, and 20 µA/cm2 for the uncoated, PSC1, and PSC2 samples, respectively. Moreover, applying these coatings also led to increasing the corrosion resistance (RP) after all the exposure periods of time. In addition, the PSC2 coating was found to be more protective against corrosion for the surface of the steel than the PSC1 coating. Full article
(This article belongs to the Special Issue Corrosion and Electrochemical Behavior of Metals Coating)
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Open AccessArticle
Low Energy Implantation of Carbon into Elastic Polyurethane
Coatings 2020, 10(3), 274; https://doi.org/10.3390/coatings10030274 - 16 Mar 2020
Viewed by 354
Abstract
Ion modification of polymeric materials requires gentle regimens and subsequent investigation of mechanical and deformation behavior of the surfaces. Polyurethane is a synthetic block copolymer: A fibrillar hard phase is inhomogeneoulsy distributed in a matrix of soft phase. Implantation of carbon ions into [...] Read more.
Ion modification of polymeric materials requires gentle regimens and subsequent investigation of mechanical and deformation behavior of the surfaces. Polyurethane is a synthetic block copolymer: A fibrillar hard phase is inhomogeneoulsy distributed in a matrix of soft phase. Implantation of carbon ions into this polymer by deep oscillation magnetron sputtering (energy—0.1–1 keV and dose of ions—1014–1015 ion/cm2) forms graphene-like nanolayer and causes heterogeneous changes in structural and mechanical properties of the surface: Topography, elastic modulus and depth of implantation for the hard/soft phase areas are different. As a result, after certain treatment regimens strain-induced defects (nanocracks in the areas of the modified soft phase, or folds in the hard phase) appear on the surfaces of stretched materials. Treated surfaces have increased hydrophobicity and free surface energy, and in some cases show good deformability without any defects. Full article
(This article belongs to the Section Surface Characterization, Deposition and Modification)
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