Enhanced electrical conductivity of anticorrosive coatings by functionalized carbon nanotubes: effect of hydrogen bonding

Carbon nanotubes (CNTs) and nanofibers (CNFs) are well-known nano additives that produce coating materials with high electrical and thermal conductivity and corrosion resistance. In this paper, coating materials incorporating hydrogen bonding offered significantly lower electrical resistance. The hydrogen bonding formed between functionalized carbon nanotubes and ethanol helped create a well-dispersed carbon nanotube network as the electron pathways. Electrical resistivity as low as 6.8 Ω⋅cm has been achieved by adding 4.5 wt.% functionalized multiwalled carbon nanotubes (MWNT-OH) to 75%Polyurethane/25%Ethanol. Moreover, the thermal conductivity of Polyurethane was improved by 332% with 10 wt.% addition of CNF. Electrochemical methods were used to evaluate the anti-corrosion properties of the fabricated coating materials. Polyurethane with the addition of 3 wt.% of MWNT-OH showed an excellent corrosion rate of 5.105×10-3 mm/year, with a protection efficiency of 99.5% against corrosive environments. The adhesion properties of the coating materials were measured following ASTM standard test methods. Polyurethane with 3 wt.% of MWNT-OH belonged to class 5 (ASTM D3359), indicating the outstanding adhesion of the coating to the substrate. These nano coatings with enhanced electrical, thermal, and anti-corrosion properties consist of a choice of traditional coating materials, such as Polyurethane, yielding coating durability with the ability to tailor the electrical and thermal properties to fit the desired application.

Method to determine particle release during long-term loading for assessment of coating durability of cardiovascular stents

Many catheters and vascular implants are coated to increase biocompatibility or to reduce friction during catheter based implantation. Several regulations require assessment of coating durability over the implant’s life time. An in vitro method for stent testing is presented to measure released particulate matter at defined inspection intervals. The method was validated using polystyrene microspheres with a size of 10, 25 and 50 μm to check for particle recovery (n=6). Two cleaning steps followed. Particle counting was performed by light obscuration method. The recovery rate was 103±5% (10μm), 94±4% (25 μm) and 78±12% (50 μm), respectively, meeting the requirements of FDA guidance documents (i.e. FDA 1545). Less than 3% of the particles were found in the cleaning solutions. The method using a fixed volume during stent loading can be adapted to all durability testers where tubes are used to fix the stents (radial pulsatile, bending, axial compression, torsion).

Ultra-thin self-healing vitrimer coatings for durable hydrophobicity

Durable hydrophobic materials have attracted considerable interest in the last century. Currently, the most popular strategy to achieve hydrophobic coating durability is through the combination of a perfluoro-compound with a mechanically robust matrix to form a composite for coating protection. The matrix structure is typically large (thicker than 10 μm), difficult to scale to arbitrary materials, and incompatible with applications requiring nanoscale thickness such as heat transfer, water harvesting, and desalination. Here, we demonstrate durable hydrophobicity and superhydrophobicity with nanoscale-thick, perfluorinated compound-free polydimethylsiloxane vitrimers that are self-healing due to the exchange of network strands. The polydimethylsiloxane vitrimer thin film maintains excellent hydrophobicity and optical transparency after scratching, cutting, and indenting. We show that the polydimethylsiloxane vitrimer thin film can be deposited through scalable dip-coating on a variety of substrates. In contrast to previous work achieving thick durable hydrophobic coatings by passively stacking protective structures, this work presents a pathway to achieving ultra-thin (thinner than 100 nm) durable hydrophobic films.

Durable anti-oil-fouling superhydrophilic membranes for oil-in-water emulsion separation

Marine mussel-inspired polydopamine (PDA) coatings show excellent hydrophilicity and substrate-independent adhesion ability, but low stability, especially in a harsh environment such as strong acid or strong base, significantly restricts their applications. In this work, we prepare a novel superhydrophilic and underwater superoleophobic coating based on a modified PDA. Diglycidyl resorcinol ether (DGRE) polyethyleneimine (PEI) and iron ions were incorporated into PDA to strengthen the cross-linking and coating durability. By using three chemically inert hydrophobic membranes, polytetrafluoroethylene (PTFE), poly(vinylidene fluoride), and polypropylene, as substrates, we showed that PDA/PEI/DGRE-coated membranes had a water contact angle (CA) of 0° and underwater oil CA above 157°, and their underwater oil SAs were <7°. The coating is durable against both physical and chemical damages including ultrasound and heat treatments, as well as acid/alkaline etching. After ultrasound treatment in water for 60 min, and heating treatment for 3 h, or acid/alkaline etching for 3 h, the coated PTFE membrane still showed water CAs of ∼0° in air and underwater oil CAs of ∼150°. The coated membranes can efficiently separate oil-in-water emulsions, even in strong acid and base environments. The water flux was above 1500 L m−2 h−1, and the oil rejection was above 99%.

Improved Tribological Performance of Polydopamine/Polytetrafluoroethylene Thin Coatings With Silica Nanoparticles Incorporated into the Polydopamine Underlayer

Polytetrafluoroethylene (PTFE) is a solid lubricant with low friction coefficient. However, it lacks durability as a thin coating. Prior studies have shown that a polydopamine (PDA) underlayer enhances the coating durability. In this study, 100, 200, and 300 µL of aqueous silica nanoparticle (NP) dispersions were added to a 15 mL PDA deposition solution. Stainless steel substrates were coated with PDA + silica in the mixed dispersions and then coated with PTFE layers to form thin PDA + silica/PTFE coatings. The coatings were tested in ball-on-flat linear reciprocating motion under dry contact conditions. The durability of the PDA/PTFE coating was improved by 70% when 100 µL of aqueous silica NP dispersion was added. The significant improvement in the durability was attributed to the increased adhesion of the PTFE coating to the PDA underlayer, the fragmented wear debris, and the enhanced counterface transfer film. These samples also showed enhanced resistance under linearly increasing load scratch testing with lower coefficient of friction (COF) and higher delamination resistance when compared to samples without silica.

Nanoindentation Hardness and Practical Scratch Resistance in Mechanically Tunable Anti-Reflection Coatings

This work presents fundamental understanding of the correlation between nanoindentation hardness and practical scratch resistance for mechanically tunable anti-reflective (AR) hardcoatings. These coatings exhibit a unique design freedom, allowing quasi-continuous variation in the thickness of a central hardcoat layer in the multilayer design, with minimal impact on anti-reflective optical performance. This allows detailed study of anti-reflection coating durability based on variations in hardness vs. depth profiles, without the durability results being confounded by variations in optics. Finite element modeling is shown to be a useful tool for the design and analysis of hardness vs. depth profiles in these multilayer films. Using samples fabricated by reactive sputtering, nanoindentation hardness depth profiles were correlated with practical scratch resistance using three different scratch and abrasion test methods, simulating real world scratch events. Scratch depths from these experiments are shown to correlate to scratches observed in the field from consumer electronics devices with chemically strengthened glass covers. For high practical scratch resistance, coating designs with hardness >15 GPa maintained over depths of 200–800 nm were found to be particularly excellent, which is a substantially greater depth of high hardness than can be achieved using previously common AR coating designs.

Evaluation of the antithrombogenicity of poly-2-methoxyethylacrylate-coated catheters

Background and objectives: The blood compatibility of indwelling intravascular catheters is facilitated by the use of antithrombogenic materials. Heparin has typically been used for this purpose; however, since heparin-coated catheters are considered combination products, difficulties meeting the relevant Food and Drug Administration safety recommendations have disrupted commercialization. Other issues include coating durability and the occurrence of heparin-induced thrombocytopenia. Polymer coatings are a potential alternative; however, polymer antithrombogenicity in circulating human blood has yet to be demonstrated. The present study aimed to establish the ex vivo antithrombogenicity of a poly-2-methoxyethylacrylate (PMEA) polymer coating applied to a central venous catheter using an artificial human blood circulation system. Methods: The present study used an artificial human blood circulation system to conduct an ex vivo evaluation of the antithrombogenicity of poly-2-methoxyethylacrylate (PMEA)-coated catheters. Human blood samples obtained from volunteer donors were loaded into a circulation system fitted with either a PMEA-coated or uncoated catheter. After 3-h, the catheter was removed and examined using scanning electron microscopy. Protein adsorption on the catheter surface was investigated by shredding the catheter that had contacted the blood inside the circulation system and immersing the pieces in 1 mL of 0.5 N NaOH for 2 days. The amount of protein in the 0.5 N NaOH was determined according to the Lowry method. Results: Adherent fibrin, which forms a sheath on the catheter surface, was observed on uncoated, but not PMEA-coated catheters. Furthermore, the amount of protein adsorption was significantly less with PMEA-coated than uncoated catheters ( p = 0.043). Conclusions: The present findings demonstrated the antithrombogenicity of PMEA-coated catheters in circulating human blood.

Environmental Barrier Coating Oxidation and Adhesion Strength

Plasma Spray- Physical Vapor Deposition (PS-PVD) environmental barrier coatings (EBCs) of Yb2Si2O7 were deposited on SiC and exposed in a steam environment (90% H2O/O2) at 1426°C to form a thermally grown oxide (TGO) layer between the substrate and EBC. In advanced ceramic material systems such as coated ceramic matrix composites (CMCs), the TGO layer is the weak interface in coated CMC systems and directly influences component lifetimes. The effect of surface roughness and TGO thickness on the adhesion strength were evaluated by mechanical testing of the coatings after exposure. Morphology and oxide layer thickness were analyzed with electron microscopy while the composition and crystal structure were tracked with X-ray diffraction. The strength of the system is evaluated with respect to oxidation rate to give a qualitative understanding of coating durability.

Environmental Barrier Coating Oxidation and Adhesion Strength

Plasma Spray-Physical Vapor Deposition (PS-PVD) environmental barrier coatings (EBCs) of Yb2Si2O7 were deposited on SiC and exposed in a steam environment (90% H2O/O2) at 1426°C to form a thermally grown oxide (TGO) layer between the substrate and EBC. In advanced ceramic material systems such as coated ceramic matrix composites (CMCs), the TGO layer is the weak interface in coated CMC systems and directly influences component lifetimes. The effect of surface roughness and TGO thickness on the adhesion strength were evaluated by mechanical testing of the coatings after exposure. Morphology and oxide layer thickness were analyzed with electron microscopy while the composition and crystal structure were tracked with X-ray diffraction. The strength of the system is evaluated with respect to oxidation rate to give a qualitative understanding of coating durability.