Special Issue "Active Organic and Organic-Inorganic Hybrid Coatings and Thin Films: Challenges, Developments, Perspectives"

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

Deadline for manuscript submissions: closed (30 June 2018)

Special Issue Editors

Guest Editor
Prof. Assunta Marrocchi

Department of Chemistry, Biology and Biotechnology, University of Perugia, 06123 Perugia, Italy
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Interests: materials design and sustainable synthesis, organic photovoltaics, flexible electronics, renewable resources
Guest Editor
Prof. Maria Laura Santarelli

Department of Chemical Materials Environmental Engineering, University of Rome Sapienza, via Eudossiana 18, 00184 Rome, Italy
Website | E-Mail
Interests: characterization techniques, polymer science, photovoltaics, photocatalytic materials, nanomaterials, protective coatings

Special Issue Information

Dear Colleagues,

During the last decade, active (also called “smart”) coatings and thin films have been  extensively explored in terms of structure material properties, processing, morphology and performance. Several types of surface-functional coatings/thin films are known to perform their functions through peculiar physical properties of their top surface, thereby achieving, e.g., good resistance to chemicals, light and temperature, excellent mechanical properties, as well as tuneable free surface energy parameters. In some cases, covering of the protected surface with such smart systems also provides active properties that may enable continuous physical/chemical protection, even after partial mechanical damage of the coverage, by self-healing effects. Further, the active properties may hint at biological effects, e.g., the release of drugs, or at photoelectric effects, as a consequence of surface doping through the use of appropriate elements. Notably, the synergic combination of organic and inorganic components in one (hybrid) material to create unique properties is considered to date among the most promising strategy towards technological innovation in the field.

This Special Issue aims at report original research and reviews focusing specifically on active organic and organic-inorganic hybrid coatings and thin films to provide the readers with a reference concerning the most updated findings in the field.   

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

• Design, synthesis and characterization; 
• Novel deposition techniques;
• Optically active organic and organic–inorganic hybrid thin films;
• Catalytically and photocatalytically active organics and hybrids;
• Active organic/organic–inorganic hybrid coatings and thin films from renewable resources;
• Bioactive and biomimetic coatings;
• Enhanced coatings performances on different substrates.

Prof. Assunta Marrocchi
Prof. Maria Laura Santarelli
Guest Editors

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 1200 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 (10 papers)

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Research

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Open AccessArticle Waterborne Acrylate-Based Hybrid Coatings with Enhanced Resistance Properties on Stone Surfaces
Coatings 2018, 8(8), 283; https://doi.org/10.3390/coatings8080283
Received: 10 July 2018 / Revised: 2 August 2018 / Accepted: 11 August 2018 / Published: 15 August 2018
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Abstract
The application of coating polymers to building materials is a simple and cheap way to preserve and protect surfaces from weathering phenomena. Due to its environmentally friendly character, waterborne coating is the most popular type of coating, and improving its performance is an
[...] Read more.
The application of coating polymers to building materials is a simple and cheap way to preserve and protect surfaces from weathering phenomena. Due to its environmentally friendly character, waterborne coating is the most popular type of coating, and improving its performance is an important key of research. The study presents the results regarding the mechanical and photo-oxidation resistance of some water-based acrylic coatings containing SiO2 nanoparticles obtained by batch miniemulsion polymerization. Coating materials have been characterized in terms of hydrophobic/hydrophilic behavior, mechanical resistance and surface morphology by means of water-contact angle, and scrub resistance and atomic force microscopy (AFM) measurements depending on silica-nanoparticle content. Moreover, accelerated weathering tests were performed to estimate the photo-oxidation resistance of the coatings. The chemical and color changes were assessed by Fourier-transform infrared spectroscopy (FTIR) and colorimetric measurements. Furthermore, the nanofilled coatings were applied on two different calcareous lithotypes (Lecce stone and Carrara Marble). Its properties, such as capillary water absorption and color modification, before and after accelerated aging tests, were assessed. The properties acquired by the addition of silica nanoparticles in the acrylic matrix can ensure good protection against weathering of stone-based materials. Full article
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Open AccessArticle Poly(Phenylene Methylene): A Multifunctional Material for Thermally Stable, Hydrophobic, Fluorescent, Corrosion-Protective Coatings
Coatings 2018, 8(8), 274; https://doi.org/10.3390/coatings8080274
Received: 29 June 2018 / Revised: 20 July 2018 / Accepted: 25 July 2018 / Published: 7 August 2018
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Abstract
Poly(phenylene methylene) (PPM) is a thermally stable, hydrophobic, fluorescent hydrocarbon polymer. PPM has been proposed earlier to be useful as a coating material but this polymer was isolated in relevant molar masses only recently, and in large quantities. Accordingly, the preparation of coatings
[...] Read more.
Poly(phenylene methylene) (PPM) is a thermally stable, hydrophobic, fluorescent hydrocarbon polymer. PPM has been proposed earlier to be useful as a coating material but this polymer was isolated in relevant molar masses only recently, and in large quantities. Accordingly, the preparation of coatings based on PPM and their behavior was explored in this study, with the example of the metal alloy AA2024 as a common substrate for corrosion tests. Coatings free of bubbles and cracks were obtained by hot pressing and application of the following steps: Coating on AA2024 with a layer of polybenzylsiloxane to improve the adhesion between PPM and the metal surface, the addition of polybenzylsiloxane to PPM in order to enhance the viscosity of the molten PPM, and the addition of benzyl butyl phthalate as a plasticizer. Electrochemical corrosion tests showed good protection of the metal surface towards a NaCl solution, thanks to a passive-like behavior in a wide potential window and a very low current density. Remarkably, the PPM coating also exhibited self-healing towards localized attacks, which inhibits the propagation of corrosion. Full article
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Open AccessFeature PaperArticle A Ladder-Type Organosilicate Copolymer Gate Dielectric Materials for Organic Thin-Film Transistors
Coatings 2018, 8(7), 236; https://doi.org/10.3390/coatings8070236
Received: 31 May 2018 / Revised: 27 June 2018 / Accepted: 2 July 2018 / Published: 3 July 2018
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Abstract
A ladder-type organosilicate copolymer based on trimethoxymethylsilane (MTMS) and 1,2-bis(triethoxysilyl)alkane (BTESn: n = 2–4) were synthesized for use as gate dielectrics in organic thin-film transistors (OTFTs). For the BTESn, the number of carbon chains (2–4) was varied to elucidate
[...] Read more.
A ladder-type organosilicate copolymer based on trimethoxymethylsilane (MTMS) and 1,2-bis(triethoxysilyl)alkane (BTESn: n = 2–4) were synthesized for use as gate dielectrics in organic thin-film transistors (OTFTs). For the BTESn, the number of carbon chains (2–4) was varied to elucidate the relationship between the chemical structure of the monomer and the resulting dielectric properties. The developed copolymer films require a low curing temperature (≈150 °C) and exhibit good insulating properties (leakage current density of ≈10−8–10−7 A·cm−2 at 1 MV·cm−1). Copolymer films were employed as dielectric materials for use in top-contact/bottom-gate organic thin-film transistors and the resulting devices exhibited decent electrical performance for both p- and n-channel organic semiconductors with mobility as high as 0.15 cm2·V−1·s−1 and an Ion/Ioff of >105. Furthermore, dielectric films were used for the fabrication of TFTs on flexible substrates. Full article
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Open AccessArticle The Potential of Functionalized Ceramic Particles in Coatings for Improved Scratch Resistance
Coatings 2018, 8(6), 224; https://doi.org/10.3390/coatings8060224
Received: 28 May 2018 / Revised: 15 June 2018 / Accepted: 16 June 2018 / Published: 19 June 2018
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Abstract
The top layer of a typical high pressure floor laminate (HPL) consists of a melamine formaldehyde (MF) impregnated special wear layer (overlay) with alumina particles. This top layer plays a crucial role in determining the mechanical properties of the laminate. For HPLs, scratch
[...] Read more.
The top layer of a typical high pressure floor laminate (HPL) consists of a melamine formaldehyde (MF) impregnated special wear layer (overlay) with alumina particles. This top layer plays a crucial role in determining the mechanical properties of the laminate. For HPLs, scratch resistance and scratch visibility are particularly important properties. This study aimed to improve the mechanical properties, particularly the scratch resistance, by adjusting the composition of the overlay. Laminates containing alumina particles were prepared and tested. These alumina particles were additionally functionalized with a silane coupling agent to ensure better adhesion between the particles and the resin. The functionalized particles led to enhanced scratch resistance of the laminates as well as improved dispersion of the particles within the resin. Micro scratch testing revealed that by using functionalized particles, the scratch surface damage was reduced and the recovery characteristics of the surface layer were improved. Higher scratch resistance and scratch hardness were thus obtained, along with a reduced scratch visibility. Full article
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Open AccessArticle Omnidirectional SiO2 AR Coatings
Coatings 2018, 8(6), 210; https://doi.org/10.3390/coatings8060210
Received: 18 April 2018 / Revised: 17 May 2018 / Accepted: 26 May 2018 / Published: 1 June 2018
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Abstract
It is of great importance to develop antireflective (AR) coatings and techniques because improved optical performance has been progressively prerequisite for wide-ranging applications such as flat panel displays, optoelectronic devices or solar cells. Natural surroundings inspire researchers considerably to impersonate in order to
[...] Read more.
It is of great importance to develop antireflective (AR) coatings and techniques because improved optical performance has been progressively prerequisite for wide-ranging applications such as flat panel displays, optoelectronic devices or solar cells. Natural surroundings inspire researchers considerably to impersonate in order to provoke analogous characteristics via artificial approaches, which provide the opportunity for emerging techniques and development in material engineering. Herein, SiO2 antireflective (AR) coatings comprised of two layers were fabricated using a physical vapour deposition method via glancing angle. The top layer fabricated at an oblique angle of 80° and the bottom layer close to the substrate was deposited at a deposition angle of 0°. The experimental outcomes demonstrate that there is a slight influence on the refractive index of thin films by changing the morphology of nanostructures keeping deposition angles the same. The top layer shows a periodic arrangement of SiO2 nanostructures while the bottom stratum represents a SiO2 compact dense layer. The assembled bilayer SiO2 AR coating retains omnidirectional AR efficiency and tunability at a preferred wavelength range displaying <1% reflectance. Moreover, the fabricated omnidirectional SiO2 AR coatings have thermal stability up to 300 °C. These SiO2 AR coatings also possess negative temperature resistivity to withstand different cold storage conditions. Hence, the flexible and environmental adaptive SiO2 AR coating offers an intriguing route for imminent research in optics. Full article
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Open AccessFeature PaperArticle Stabilized SPEEK Membranes with a High Degree of Sulfonation for Enthalpy Heat Exchangers
Coatings 2018, 8(5), 190; https://doi.org/10.3390/coatings8050190
Received: 18 April 2018 / Revised: 10 May 2018 / Accepted: 16 May 2018 / Published: 19 May 2018
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Abstract
In this investigation, we explored for the first time the use of cross-linked sulfonated poly (ether ether ketone) (SPEEK) membranes in the fabrication of enthalpy heat exchangers. SPEEK is very sensitive to changes in relative humidity, especially when featuring high degrees of sulfonation
[...] Read more.
In this investigation, we explored for the first time the use of cross-linked sulfonated poly (ether ether ketone) (SPEEK) membranes in the fabrication of enthalpy heat exchangers. SPEEK is very sensitive to changes in relative humidity, especially when featuring high degrees of sulfonation (DS), though a poor mechanical stability may be observed in the latter case. Cross-linking is crucial in overcoming this issue, and here, we firstly employed the INCA method (ionomer counter-elastic pressure “nc” analysis) to assess the improvements in the mechanical properties. The cross-link was achieved following a simple thermal-assisted process that occurs directly on the performed membranes. After an initial screening, a degree of cross-link = 0.1 was selected as the better compromise between absorption of water vapor and mechanical properties. When implemented in the enthalpy heat exchanger system, these cross-linked SPEEK membranes enabled a high level of sensible heat exchange, as well as a remarkable variation in the mass (water vapor) transfer between the individual air flows. The performances resulted in being better than those for the system based on a benchmark commercially available perfluorinated Nafion membrane. Full article
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Open AccessArticle Corrosion Inhibition Properties of Waterborne Polyurethane/Cerium Nitrate Coatings on Mild Steel
Received: 26 September 2017 / Revised: 2 January 2018 / Accepted: 10 January 2018 / Published: 15 January 2018
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Abstract
Waterborne polyurethane (WBPU)/cerium nitrate (Ce(NO3)3) dispersions were synthesized with different defined Ce(NO3)3 content. All pristine dispersions were stable with different poly(tetramethylene oxide) glycol (PTMG) number average molecular weights (Mn) of 650, 1000, and 2000. The interaction
[...] Read more.
Waterborne polyurethane (WBPU)/cerium nitrate (Ce(NO3)3) dispersions were synthesized with different defined Ce(NO3)3 content. All pristine dispersions were stable with different poly(tetramethylene oxide) glycol (PTMG) number average molecular weights (Mn) of 650, 1000, and 2000. The interaction between the carboxyl acid salt group and Ce(NO3)3 was analyzed by Fourier-transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) techniques. Coating hydrophilicity, water swelling (%), water contact angle, leaching, and corrosion protection efficiency were all affected when using different Ce(NO3)3 content and PTMG molecular weights. The maximal corrosion protection of the WBPU coating was recorded using a higher molecular weight of PTMG with 0.016 mole Ce(NO3)3 content. Full article
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Open AccessArticle Anti-Corrosive and Scale Inhibiting Polymer-Based Functional Coating with Internal and External Regulation of TiO2 Whiskers
Received: 21 November 2017 / Revised: 12 December 2017 / Accepted: 2 January 2018 / Published: 9 January 2018
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Abstract
A novel multi-functional carrier of mesoporous titanium dioxide whiskers (TiO2(w)) modified by ethylenediamine tetra (methylene phosphonic acid) (EDTMPA) and imidazoline was devised in epoxy coating to improve the anti-corrosion and scale inhibition properties of metal surface. Rigorous characterization using analytical techniques
[...] Read more.
A novel multi-functional carrier of mesoporous titanium dioxide whiskers (TiO2(w)) modified by ethylenediamine tetra (methylene phosphonic acid) (EDTMPA) and imidazoline was devised in epoxy coating to improve the anti-corrosion and scale inhibition properties of metal surface. Rigorous characterization using analytical techniques showed that a mesoporous structure was developed on the TiO2(w). EDTMPA and imidazoline were successfully grafted on the outer and inner surfaces of mesoporous TiO2(w) to synthesize iETiO2(w). The results demonstrated that the corrosion resistance of the final iETiO2(w) epoxy coating is 40 times higher than that of the conventional unmodified OTiO2(w) epoxy coating. The enhanced corrosion resistance of the iETiO2(w) functional coating is due to the chelation of the scaling cations by EDTMPA and electron sharing between imidazoline and Fe. Scale formation on the iETiO2(w) coating is 35 times lower than that on the unmodified OTiO2(w) epoxy coating. In addition, EDTMPA and imidazoline act synergistically in promoting the barrier property of mesoporous TiO2(w) in epoxy coating. It is believed that this novel, simple, and inexpensive route for fabricating functional surface protective coatings on various metallic materials will have a wide range of practical applications. Full article
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Open AccessArticle IPN Polysiloxane-Epoxy Resin for High Temperature Coatings: Structure Effects on Layer Performance after 450 °C Treatment
Coatings 2017, 7(12), 213; https://doi.org/10.3390/coatings7120213
Received: 23 October 2017 / Revised: 21 November 2017 / Accepted: 22 November 2017 / Published: 28 November 2017
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Abstract
Coatings for high temperatures (HT > 400 °C) are obtained from interpenetrating polymer network (IPN) binders formed by simultaneous polymerization of silicone and epoxide pre-polymers. A ceramic layer; mainly composed of silica and fillers; remains on the metal surface after a thermal treatment
[...] Read more.
Coatings for high temperatures (HT > 400 °C) are obtained from interpenetrating polymer network (IPN) binders formed by simultaneous polymerization of silicone and epoxide pre-polymers. A ceramic layer; mainly composed of silica and fillers; remains on the metal surface after a thermal treatment at 450 °C. The layer adhesion and the inorganic filler’s distribution have been investigated by, firstly, exchanging the organic substituents (methyl and phenyl) of the silicone chains and, secondly, by adding conductive graphene nanoplatelets with the aim to assure a uniform distribution of heat during the thermal treatment. The results are evidence that different substituent ratios affect the polymer initial layout. The adhesion tests of paint formulations are analysed and were related to instrumental analyses performed using glow discharge optical emission spectroscopy (GDOES); thermal analyses (TG/DTA and DSC); electron microscopy with energy dispersive X-ray analysis (SEM-EDX). A greater resistance to powdering using phenyl groups instead of methyl ones; and an improved distribution of fillers due to graphene nanoplatelet addition; is evidenced. Full article
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Review

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Open AccessReview Novel Attribute of Organic–Inorganic Hybrid Coatings for Protection and Preservation of Materials (Stone and Wood) Belonging to Cultural Heritage
Coatings 2018, 8(9), 319; https://doi.org/10.3390/coatings8090319
Received: 4 July 2018 / Revised: 5 September 2018 / Accepted: 6 September 2018 / Published: 10 September 2018
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Abstract
In order to protect a material belonging to Cultural Heritage (i.e., stone, wood) from weathering, and in turn to preserve its beauty and historical value for the future generations, the contact with external harmful agents, particularly water, must be avoided, or at least
[...] Read more.
In order to protect a material belonging to Cultural Heritage (i.e., stone, wood) from weathering, and in turn to preserve its beauty and historical value for the future generations, the contact with external harmful agents, particularly water, must be avoided, or at least limited. This task can be successfully obtained with the use of a protective organic coating. The use of nano-metric reinforcing agents in conventional polymeric coatings demonstrated to be a successful route in achieving better protective performance of the films and improved physical properties, even in extreme environments. The present paper would, therefore, review the more recent findings in this field. Generally speaking, when a hydrophobic product is applied on its surface, the stone material will absorb less water and consequently, less substances which may be harmful to it. An efficient organic coating should also supply wear and abrasion resistance, resistance to aggressive chemicals, excellent bond to the substrate; finally, it should be also able to guarantee vapor exchange between the environment and the material interior, i.e., the material should keep the same water vapor permeability as if it was un-protected. To regard to the conservation of wood artifacts, protective treatments for wood will preserve the material from environmental agents and biological attack. Hence, potential advantages of hybrid (organic–inorganic) nano-composite coatings for stone/wood have been found to be: Enhanced mechanical properties in comparison to the pure polymeric matrix, due to the reinforcing effect of the nano-filler; superior barrier properties (the presence of the nano-filler hinders the ingress of water and/or potentially harmful chemicals); optical clarity and transparency. It has been found that the efficacy of a nano-filled coating strongly depends on the effectiveness of the method used to uniformly disperse the nano-filler in the polymeric matrix. Furthermore, the presence of nano-particles should not impair the viscosity of the organic matrix, in order to employ the conventional techniques of application for coatings. Full article
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