Special Issue "Thin Films and Coatings by Sol-Gel Chemistry: Synthesis, Characterization and Applications"

A special issue of Coatings (ISSN 2079-6412).

Deadline for manuscript submissions: 31 July 2021.

Special Issue Editor

Prof. Dr. Michelina Catauro
Website
Guest Editor
Department of Engineering, University of Campania “Luigi Vanvitelli”, Via Roma 29, I-81031 Aversa, Italy
Interests: sol-gel technology; biomaterials; bioglass; organic-inorganic hybrid materials; drug delivery; thin films
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Special Issue Information

Dear Colleagues,

Chemical and physical features of material surfaces are closely related to many material properties, such as hydrophilicity and hydrophobia, wear and corrosion resistance, biological performances (e.g., bioactivity and biocompatibility) and optical properties (e.g., refraction index, reflection, photoluminescence). Therefore, the deposition of functional coatings to modify material surfaces nowadays represents a promising strategy to give new properties to the materials or to modify and/or improve some already existing ones. One of the most feasible technology to produce homogeneous and functional coatings with a wide range of properties is the sol-gel technique. It is a method to synthesize glass and ceramic oxides at low temperature. The process involves the hydrolysis of a metal alkoxide precursor dissolved in a water-alcohol solution, and the polycondensation of the formed oligomers which leads to the transition of the system from a mostly colloidal liquid (‘sol’) into a solid wet ‘gel’. Further processing of the sol and the possibility of coupling the sol-gel process with a coating technique (e.g., dip coating, spin coating or spry coating) make it an interesting approach for the preparation of thin film with potential advantages, such as higher purity and homogeneity of the obtained layers, lower processing temperatures, reduced thickness, easy method of preparation and ability to form coatings over large surfaces and substrates with complex geometric shapes, allowing a good control of the composition and properties of the final layers.

For this reason, the sol-gel coatings are usefully used in a wide area of applications, such as biology and medicine, environment, optics, electronics, energy, catalysts, sensors and functional smart coatings.

It is my pleasure to invite you to submit a manuscript for this Special Issue.

In particular, the topics of interest include, but are not limited to:

  • Techniques for coating preparation;
  • Techniques for the characterization of the chemical coating structure and microstructure;
  • Characterization of coating properties (biological performances, mechanical behavior, optical properties, etc.);
  • Applications of sol-gel coatings (protective coatings, optical coatings, coatings for biomedical applications, etc.);
  • Organic–inorganic hybrid coatings and their applications.

Prof. Michelina Catauro
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Coatings is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Published Papers (5 papers)

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Research

Open AccessArticle
A Study of the Optical Properties and Fabrication of Coatings Made of Three-Dimensional Photonic Glass
Coatings 2020, 10(8), 781; https://doi.org/10.3390/coatings10080781 - 12 Aug 2020
Abstract
Photonic crystals employ optical properties based on optical, physical, chemical, and material science. Nanosilica particles have a high specific surface area and are widely used in nanotechnology research and biomedical applications. In this study, nanosilica particles were fabricated by sol–gel methods, and the [...] Read more.
Photonic crystals employ optical properties based on optical, physical, chemical, and material science. Nanosilica particles have a high specific surface area and are widely used in nanotechnology research and biomedical applications. In this study, nanosilica particles were fabricated by sol–gel methods, and the particle sizes of the silica nanoparticles were 280, 232, and 187 nm, based on dynamic light scattering. The silica nanoparticle suspension solution was heated to boiling for fast evaporation processing for self-assembly to fabricate three-dimensional photonic glass for structural color coatings. The sample had an adjustable structural color (red: 640 nm, green: 532 nm, and blue: 432 nm). The microstructures of various structure-colored samples were arranged, but there was a disordered solid arrangement of silica nanoparticles. These were not perfect opal-based photonic crystals. Compared to opal-based photonic crystals, the arrangement of silica nanoparticles was a glassy structure with a short-range order. Due to the accumulation of silica nanoparticle aggregates, samples displayed a stable colloidal film, independent of the viewing angle. In our study, the fast solvent evaporation in the self-assembly process led to the formation of a colloidal amorphous array, and it fitted the requirement for non-iridescence. Non-iridescent photonic glass with various colors was obtained. This type of color coating has wide potential applications, including reflective displays, colorimetric sensors, textiles, and buildings. Full article
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Open AccessFeature PaperArticle
Use of the Sol–Gel Method for the Preparation of Coatings of Titanium Substrates with Hydroxyapatite for Biomedical Application
Coatings 2020, 10(3), 203; https://doi.org/10.3390/coatings10030203 - 26 Feb 2020
Cited by 5
Abstract
Hydroxyapatite (HA) was coated onto the surface of commercially pure titanium grade 4 (a material generally used for implant application) by a dip coating method using HA sol. Hydroxyapatite sol was synthesized via sol–gel using Ca(NO3)2∙4H2O and [...] Read more.
Hydroxyapatite (HA) was coated onto the surface of commercially pure titanium grade 4 (a material generally used for implant application) by a dip coating method using HA sol. Hydroxyapatite sol was synthesized via sol–gel using Ca(NO3)2∙4H2O and P2O5 as precursors. The surface of the HA coating was homogeneous, as determined by scanning electron microscopy (SEM), attenuated total reflectance Fourier transform infrared (ATR-FTIR), and X-ray diffraction (XRD), which allowed the materials to be characterized. The bioactivity of the synthesized materials and their efficiency for use as future bone implants was confirmed by observing the formation of a layer of hydroxyapatite on the surface of the samples soaked in a fluid simulating the composition of human blood plasma. To verify the biocompatibility of the obtained biomaterial, fibroblasts were grown on a glass surface and were tested for viability after 24 h. The results of the WST-8 analysis suggest that the HA systems, prepared by the sol–gel method, are most suitable for modifying the surface of titanium implants and improving their biocompatibility. Full article
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Open AccessArticle
Solution-Processed Mg-Substituted ZnO Thin Films for Metal-Semiconductor-Metal Visible-Blind Photodetectors
Coatings 2019, 9(4), 277; https://doi.org/10.3390/coatings9040277 - 25 Apr 2019
Cited by 8
Abstract
The effects of Mg on the microstructural, optical, and electrical properties of sol-gel derived ZnO transparent semiconductor thin films and the photoelectrical properties of photodetectors based on MgxZn1−xO (where x = 0 to 0.3) thin films with the [...] Read more.
The effects of Mg on the microstructural, optical, and electrical properties of sol-gel derived ZnO transparent semiconductor thin films and the photoelectrical properties of photodetectors based on MgxZn1−xO (where x = 0 to 0.3) thin films with the metal-semiconductor-metal (MSM) configuration were investigated in this study. All the as-synthesized ZnO-based thin films had a single-phase wurtzite structure and showed high average transmittance of 91% in the visible wavelength region. The optical bandgap of MgxZn1−xO thin films increased from 3.25 to 3.56 eV and the electrical resistivity of the films rose from 6.1 × 102 to 1.4 × 104 Ω·cm with an increase in Mg content from x = 0 to x = 0.3. Compared with those of the pure ZnO thin film, the PL emission peaks of the MgZnO thin films showed an apparent blue-shift feature in the UV and visible regions. The photo-detection capability was investigated under visible, UVA, and UVC light illumination. Linear I-V characteristics were obtained in these ZnO-based photodetectors under dark and light illumination conditions, indicating an ohmic contact between the Au electrodes and ZnO-based thin films. It was found that the pure ZnO photodetector exhibited the best photoconductivity gain, percentage of sensitivity, and responsivity under UVA illumination. Under UVC illumination, the photoconductivity gain and percentage of sensitivity of the MgZnO photodetectors were better than those of the pure ZnO photodetector. Full article
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Open AccessFeature PaperArticle
Coating of Titanium Substrates with ZrO2 and ZrO2-SiO2 Composites by Sol-Gel Synthesis for Biomedical Applications: Structural Characterization, Mechanical and Corrosive Behavior
Coatings 2019, 9(3), 200; https://doi.org/10.3390/coatings9030200 - 19 Mar 2019
Cited by 15
Abstract
The use of metallic materials as implants presents some major drawbacks, such as their harmful effects on the living organism, especially those induced by corrosion. To overcome this problem, the implant surface of titanium implants can be improved using a coating of bioactive [...] Read more.
The use of metallic materials as implants presents some major drawbacks, such as their harmful effects on the living organism, especially those induced by corrosion. To overcome this problem, the implant surface of titanium implants can be improved using a coating of bioactive and biocompatible materials. The aim of this work is the synthesis of SiO2/ZrO2 composites with different percentages of zirconia matrix (20, 33 and 50 wt.%), by the sol-gel method to coat commercial Grade 4 titanium disks using a dip coater. Attenuated total reflectance Fourier transform infrared (ATR/FTIR) spectroscopy was used to evaluate the interactions between the inorganic matrices. Furthermore, the mechanical properties and corrosive behavior of the SiO2/ZrO2 coatings were evaluated as a function of the ZrO2 content. The bioactive properties of the substrate coated with different composites were evaluated using simulated body fluid (SBF). The antibacterial activity was tested against gram-negative and gram-positive Escherichia coli and Enterococcus faecalis, respectively, to assess the release of toxic products from the different composites and to evaluate the possibility of using them in the biomedical field. Full article
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Open AccessArticle
Luminescence Properties of Co-Doped Eu3+, Bi3+ Lu2O3/Polyvinylpyrrolidone Films
Coatings 2018, 8(12), 434; https://doi.org/10.3390/coatings8120434 - 27 Nov 2018
Cited by 2
Abstract
The effect of the polyvinylpyrrolidone (PVP, MW = 130,000) molar content, PVP/Lu = 1, 2.5, 4 and 5; on the photoluminescent and structural properties of sol-gel derived Lu2O3:Eu3+, Bi3+ has been analyzed. Thin hybrid films [...] Read more.
The effect of the polyvinylpyrrolidone (PVP, MW = 130,000) molar content, PVP/Lu = 1, 2.5, 4 and 5; on the photoluminescent and structural properties of sol-gel derived Lu2O3:Eu3+, Bi3+ has been analyzed. Thin hybrid films were deposited by means of the dip-coating technique on silica quartz substrates. Films deposited at 700 °C presented a cubic structure, with non-preferential orientation, even with the presence of PVP. The photoluminescence (PL) spectrum and Comission Internationale de l’Éclairage (CIE) chromaticity diagram of films revealed a reddish Eu3+ emission at 612 nm (5D07F2) with an excitation at 320 nm of the Bi ions (6s2 → 6s6p), showing a highly-effective energy transfer process form Bi3+ to Eu3+ luminescent centers. On the other hand, the color temperature of the samples is strongly dependent on the PVP content, as a consequence of the observed difference on the branching ratios of 5D07FJ transitions of europium ions. Lifetime studies present two different behaviors for the thin films: A non-exponential nature for the lower PVP contents, and a simple exponential nature for the highest PVP one, showing that the PVP tends to promote a better dissolution of segregates and, therefore, increases the lifetime of the Eu3+ emission. Full article
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Planned Papers

The below list represents only planned manuscripts. Some of these manuscripts have not been received by the Editorial Office yet. Papers submitted to MDPI journals are subject to peer-review.

1. Author: Prof. Giuseppina Raffaini;  Politecnico di Milanodisabled, Milan, Italy
   Title: Albumin subdomain adsorption on different crystallographic faces and of an ideal nanocrystal of TiO2 anatase: a molecular dynamics study

2. Author: Prof.  Ignazio Blanco; Università degli Studi di Cataniadisabled, Catania, Italy

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