Hybrid nanocomposite coatings were prepared by the UV‐curing technique with a methacrylic oligomer and multifunctional methacrylic polyhedral oligomeric silsesquioxane blocks (POSS®). The results obtained from the polyhedral compounds were compared with those of a disordered framework obtained by the condensation of a silica precursor (MEMO). The inorganic domains generated during synthesis created constraints in movement of polymer segments, which reflected in an increase in Tg of the hybrid nanocomposite coatings. The films were transparent. The random structure obtained by the condensation of the MEMO showed a stronger effect on Tg than that observed by introducing POSS®. The effect of inorganic domains reflected on thermal stability, surface hardness and mechanical properties of the hybrid nano‐composite coatings.
An aqueous dispersion of gold nanoparticles was added to an acrylic resin and UV‐cured. The photopolymerization process was followed by means of real‐time FT‐IR spectroscopy. Nanostructured coatings containing a homogeneous dispersion of gold nanoparticles with an average size range of 20–25 nm were achieved. Macroscopic aggregation during polymerization was avoided due to the rapid initiation and kinetic associated with the photopolymerization technique, which allowed the medium to quickly solidify around the dispersion particles.
Nanocomposite UV coatings with adjustable properties for use on wood substrates in outdoor conditions were developed. Nanoscale ZnO was shown to be an efficient light absorber. Coatings were characterized in terms of elongation at brake, residual PI and double bond conversion, universal hardness, transparency, hydrophobicity, and yellowing. Coated samples were artificially weathered and studied with regard to their optical and mechanical properties, as well as to changes in brightness, transparency, hydrophobicity, and water permeability. The prepared wood coatings showed an increased weather fastness and improved optical properties. The suitability for use in outdoor conditions was assured by optimizing the elasticity of the coating and decreasing its water permeability.
Iron‐oxide nanoparticles were functionalized with epoxy groups and were dispersed into a dicyclo‐aliphatic epoxy resin to obtain organic‐inorganic hybrid coatings via cationic ring‐opening photopolymerization. TEM investigations confirmed that the filler has a size‐distribution range between 5 to 20 nm, without the formation of aggregates. The influence of the presence of Fe2O3 on the rate of polymerization was investigated by real time FT‐IR spectroscopy. Increasing the iron‐oxide nanofiller in the photocurable resin induced an increase in the Tg values. By controlling the phase separation it was possible to obtain transparent iron‐oxide nanostructured coatings, characterized by improved hardness.
Acrylate‐based nanocomposite coatings prepared from uniformly sized, nanoscaled inorganic, i.e., BaSO4‐ and CaF2‐ as well as organometallic, i.e., Al‐maleate‐derived nanoparticles were prepared applying photochemical curing. Excellent mechanical and thermal stability as well as high optical transparency was achieved as compared to standard SiO2‐based coatings. The performance of CaF2‐based nanocomposites could be further enhanced by addition of nanocorundum. A comprehensive data set on surface and Martens hardness, the penetration depths, glass transition temperatures, and UV–Vis transparency of the final coatings is presented.
The scientific and industrial history of polyurethane wire enamels during the previous six decades is reviewed. Their main use is as coatings for wires in miniature electrical devices and in electronics, where fast solderability at low temperatures is crucial. Market trends for polyurethane enamels are discussed, and an outlook is provided as to how future developments might influence the industrial use of polyurethane wire enamels.
Nowadays, nanoporous films are widely employed in biochemical applications or in opto‐photonic devices such as displays, solar cells, or light‐guiding systems. In particular, the technological feasibility of nanoporous layers with low refractive indices has recently enabled the development of high‐efficiency anti‐reflection coatings. In this paper, we report on hybrid polymer nanoporous films that can be fabricated in a single coating step with an industrial aqueous‐based method on very large surfaces. Both high transparency and low refractive index are simultaneously achieved over the entire visible spectrum. We eventually demonstrate the potential of such films for broadband AR applications by combining them in a graded‐index multilayer that reduces the surface reflectivity of a polymer substrate from 10% to few ‰.
An easy and robust approach for the production of long‐term‐stable silver nanoparticle dispersions with narrow size distribution (mean diameter ≈3–5 nm) has been developed. Amphiphilic‐modified hyperbranched polyethyleneimines with core/shell architecture were used as macromolecular templates and carriers. We systematically investigated the antibacterial performance and morphology of thin silver‐loaded hyperbranched polymer coatings on poly(ethylene terephthalate) prepared by different wet coating techniques. Furthermore, the influence of the density of the hydrophobic shell, varied by the degree of amidation between 50 and 70%, was studied with respect to the silver release behavior, wetting properties and antibacterial activity of the silver/hbp hybrid surface coatings.
Nano‐sized bis(dihydroxyaluminum)maleate particles (ALMAL) were prepared via a high‐temperature precipitation reaction from different Al‐alkoxides and maleic acid in different solvents. Variations in the reactants were carried out to identify the optimum reaction conditions that lead to particles <30 nm in diameter with narrow particle size distributions and without formation of a secondary amorphous phase. A disc centrifuge was used to characterize the particles in terms of particle size distribution. ALMAL‐containing, epoxy‐based nanocomposites were prepared with ALMAL‐loadings up to 30 wt.‐% and thermally cured. The cured coatings possessed excellent scratch and abrasion resistance, surface hardness and were highly transparent (T>95%). In order to study the effect of the nature of nanoparticles on the final properties of the coatings, aluminum malate (ALMALAT), and aluminum terephthalate (ALTEREPHTHAL) nanoparticles as well as the corresponding composite coatings were prepared and characterized. For comparison, surface‐modified silica nanoparticles were used to evaluate the mechanical and optical behavior of the produced nanocomposite coatings.
Targeting specific aerospace coating applications, highly conductive carbon nanotubes were rigorously dispersed into a commercial topcoat PU matrix to produce nanocomposites for electrostatic dissipation and/or de‐icing coatings. Systematic evaluation on a range of properties that are pertaining to the targeted applications showed that, comparing with pure PU film, an addition of 1 wt.‐% functionalized MWNTs resulted in a significant improvement in the tensile strength and modulus; a 6.5 °C shift in glass transition temperature; a six orders of magnitude decrease in electrical resistivity and 24% improvement in thermal diffusivity. The durable, light color, and flexible nanocomposite with sufficiently low surface resistivity meet the requirements for aerospace coating applications.
A magnetic microrheometer is used to characterize the development of viscosity at different depths in UV‐cured epoxy coatings. Lateral magnetic particle velocities are tracked at different depths to quantify viscosity gradients. In general, viscosity build‐up is faster near the coating surface, tending to produce a “skin”. The effects of process conditions on the viscosity gradient development, on the rate of viscosity increase, and on surface defects are studied. More severe gradients develop in thicker coatings and in those with higher photoinitiator concentration. Under some conditions, the skin layer wrinkles, indicating the development of local compressive stress. Curing at higher temperature, however, increases cure rates while reducing the viscosity gradients and wrinkling defects.
Surface properties of epoxy coatings are modified by PDMS additives in cationic UV curing of a cycloaliphatic epoxy resin. The cured films show a very high hydrophobicity that does not depend on PDMS concentration, indicating that a threshold is reached even at 0.3 wt% additive. A slight increase of the water contact angle as a function of PDMS molecular weight is observed. The additive selectively modified the air‐side of the film, while the glass‐side retains the surface properties of the pure resin. This segregation phenomenon permits to obtain highly hydrophobic films with still good adhesion properties on polar substrates, which is an important advantage over common surface‐modified resins.
A fluorinated acrylic resin was synthesized for use as a co‐monomer with a commercially available epoxy resin for UV‐cured interpenetrating polymer network preparation. Hybrid IPN networks were achieved with morphology ranging from a co‐continuous IPN to complete phase separation simply by changing monomer ratios. Highly hydrophobic coatings with good adhesion properties on glass substrates were obtained.
UV‐cured polysiloxane epoxy coatings containing titanium dioxide were prepared by means of a cationic photopolymerization process. A good distribution of the inorganic filler was achieved within the polymeric network with an average size dimension of around 500 nm. UV‐vis analysis performed on organic dye (methylene blue) stained coatings showed a high efficiency of the titania photocatalytic activity: a complete degradation of the dye on the coating surface is reached after 60 min of UV irradiation without affecting the matrix photo‐degradation.
Nanoparticles based on Al(III) and Zr(IV) melamine phosphate and sulfate, respectively, are prepared. Cone calorimeter measurements reveal that compared to an unfilled polyacrylate matrix the polyacrylate‐based nanocomposites containing the novel nanoparticles display significantly improved flame‐retardant properties as evidenced by the corresponding values for the peak heat release rate, the time‐to‐ignition, the values for the peak rate of heat release, the total heat evolved, the time to the CO peak and the CO yield. Concomitantly, the mechanical properties of the acrylate‐based composite coatings, i.e., the Martens and surface hardness, can also be significantly improved.
Water‐dispersed graphene oxide sheets were used to prepare graphene/poly(ethylene glycol) diacrylate resin composites by photopolymerization. It was found that graphene sheets undergo excellent morphological distribution within the resin system, giving rise to transparent composites with unaltered thermal properties with respect to the neat resin, that are electrically conductive at loading ratios as low as 0.02 wt.‐% of graphene oxide. The proposed strategy based on photopolymerization provides an easy, energy‐saving and environmental friendly technique that can find a wide application in coating technology, mainly for electromagnetic shielding and antistatic coatings.
In this work, polyacrylonitrile (PAN) and carbon nanofibers with controllable nanoporous structures were successfully prepared via electrospinning technique. For the preparation of porous PAN nanofibers, two kinds of polymers of PAN and polyvinylpyrrolidone (PVP) were used as electrospun precursor materials, and then the bicomponent nanofibers of PAN and PVP were extracted with water to remove the PVP in the composite polymer nanofibers. By altering the ratio of PAN/PVP in the precursor, the pore size and pore distribution of porous PAN nanofibers could be easily controlled. By using the porous PAN nanofibers as structures directing template and through heat treatment, carbon nanofibers with nanoporous structures were obtained. The porous nanofibers were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT‐IR), differential thermal analyses (DTA), Brunauer–Emmett–Teller (BET) nitrogen adsorption, X‐ray diffraction (XRD), and Raman spectra.
Castor‐oil‐based anionic PU dispersions are post‐cured using a multiaziridine‐based crosslinker CX‐100. Thermal and mechanical properties of the resulting films are studied by DMA, DSC, TGA, and tensile tests. Mechanical properties are dramatically improved by the crosslinker. For example, the Young's modulus and tensile strength increase from 14.5 to 125 MPa and 13.1 to 18.1 MPa, respectively, when the aziridine fraction increases from 0 to 100%. The onset decomposition temperature of the films, T5, increases from 162 to 209 °C, indicating a significant increase in the thermal stability as the amount of aziridine is increased. This work provides an effective way of curing biorenewable anionic PU dispersions to prepare high performance, environmentally friendly coatings.
UV‐cured photoluminescent coatings emitting in the visible spectral region are obtained by dispersing Gd2O3:4 mol% Eu3+ nanorods in three different commercially available photocurable epoxy resins. The effect of the concentration of the Gd2O3:4 mol% Eu3+ nanorods on the kinetics of the photocuring reaction is followed using real‐time FT‐IR. Thermal and the mechanical properties of the cured films are also investigated. Moreover, the effect of the matrix and nanorod concentration in the composites on the emission and excitation spectra and the 5D0(C2) decay time of Eu3+ is evaluated. The composite materials present original photoluminescence properties and demonstrate the potential of UV curing as a technique to develop smart photoactive coatings.
SBS nanocomposites based on a SBS triblock copolymer containing different weight fractions of a commercial Cloisite 20A organoclay were prepared by melt‐processing. Extensive electron microscopy as well as WAXS and static tensile and tensile creep tests were used to evaluate the resulting morphological and mechanical properties of the nanocomposites. The nanocomposite morphology is characterized by a combination of intercalated and partly exfoliated clay platelets with occasional clay aggregates present at higher clay contents; nanocomposite features that are reflected by the results of both the static tensile as well as the tensile creep tests at room temperature. For this particular thermoplastic elastomer nanocomposite system, well dispersed nanoclays lead to an enhanced stiffness and ductility; effects that induce promising improvements in nanocomposite creep performance.
