Electrochemical synthesis and anticorrosive properties of Nafion-poly(aniline-co-o-aminophenol) coatings on stainless steel

The objective of this work was to compare the electrochemical behavior and possible anticorrosive properties of composite with Nafion^®, poly(aniline-co-o-aminophenol) (P(An-co-OAP)) and polyaniline (PAn) films with those of corresponding simple films. The electrochemical synthesis of polymer films was carried out on stainless steel AISI 304 (SS) surfaces by using the cyclic potential sweep (CPS) deposition. Scanning electron microscopy (SEM) was used for the characterization of the structure and morphology of deposited films. Evaluation of anticorrosive properties of films in 0.5 M H₂SO₄ without and with chlorides was achieved by monitoring the open circuit potential (E_OC) of coated SS electrodes as well as by tracing the anodic current-potential polarization curves. These studies have shown that the SS remains in its passive state in the presence of polymer coatings. Composite with Nafion^®, P(An-co-OAP) and PAn films, keep their redox activity in chloride-containing acid solutions providing almost a complete protection of the SS substrate against pitting corrosion. These films prevent chloride exchange with solution because of the cation permselectivity of the Nafion^® membrane. The charge compensation during redox reactions occurs mainly by protons since sulfonate groups of Nafion^® act as dopants in composite films. The redox behavior of the Nafion^®-P(An-co-OAP) film is improved as compared with that of the Nafion^®-PAn film in both Cl⁻-free and Cl⁻-containing solutions. This behavior may be ascribed to the functional group -OH that facilitates charge compensation through proton during redox reactions.     

Pool boiling fouling and corrosion properties on liquid‐phase‐deposition TiO2 coatings with copper substrate

Fouling on the heat transfer surfaces of industrial heat exchangers is an intractable problem, and several techniques have been suggested to inhibit fouling. Surface coatings are of such techniques by which the adhesion force between fouling and heat transfer surface can be reduced with low surface free energy thin films. In this article, liquid phase deposition was applied to coat titanium dioxide thin films on the red copper substrates with film thickness in micro‐ or nano‐meter scale. Coating thickness, contact angle, roughness, surface topography, and components were measured with X‐ray diffraction, contact angle analyzer, stylus roughmeter, scanning electron microscopy, and energy dispersive X‐ray spectroscopy, respectively. Surface free energy of coating layers was calculated based on the contact angle. Heat transfer and fouling characteristics in pool boiling of distilled water and calcium carbonate solution on coated surfaces were investigated. Heat transfer enhancement was observed on coated surfaces compared with untreated or polished surfaces due to the micro‐ and nano‐structured surfaces which may increase the number of nucleation sites. The nonfouling time on the coated surfaces is extended than that on the untreated or polished surfaces due to the reducing of the surface free energy of coated surfaces. Corrosion behavior of coated surfaces soaked in the corrosive media of hydrochloric acid, sodium hydroxide alkali, and sodium chloride salt solutions with high concentration at room temperature a few hours was also explored qualitatively. Anticorrosion results of the coated surfaces were obtained. The coatings resisted alkali corrosion within 7.2 × 10⁵ s, acidic corrosion within 3.6 × 10⁵ s and salt corrosion within 2.16 × 10⁶ s. The present work may open a new coating route to avoid fouling deposition and corrosion on the heat transfer surfaces of industry evaporators, which is very important for energy saving in the related industries. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Effects of casting and post casting annealing on xylene isomer transport properties of Torlon 4000T films

Procedures for Torlon^® 4000T membrane formation were developed to provide attractive and repeatable xylene separation properties. Torlon^® 4000T membrane films cast by our method were investigated in terms of thermally induced imidization, molecular weight enhancement, and solvent removal. After development of the Torlon^® 4000T casting procedure, pervaporation of a xylene mixture (i.e. 30% para-xylene, 30% meta-xylene, 30% ortho-xylene, and 10% ethylbenzene) was performed in both Torlon^® 4000T and post casting annealed Torlon^® 4000T films. The xylene pervaporation in annealed Torlon^® 4000T film at 200 °C gave a permeability of 0.25 Barrer and a selectivity of 3.1 (para/ortho) and 2.1 (para/meta) respectively. A so-called “permeability collapse” reflecting an accelerated reduction in the free volume is consistent with significant temperature-induced changes in the films observed after thermal annealing at 300 °C. This conditioning effect is induced by a combination of heat treatment and the presence of the interacting aromatic penetrants. Optical methods were used to verify that the density of annealed samples exposed to xylene for 5 days eventually increased, suggesting that the membrane is originally swollen upon initial xylene exposure, and then relaxes to a more densified, and more discriminating state.     

An Electrochemical and XPS Study of Ag–Pb Binary Alloys incorporated in Nafion® Coatings

Glassy carbon electrodes coated with thin films of Nafion^® metalized with silver and lead species were investigated by cyclic voltammetry, chronoamperometry and X-ray photoelectron spectroscopy (XPS). Metalization of Nafion^® film was accomplished by dipping the coated electrodes in 3 mM AgNO₃ + 3mM Pb(NO₃)₂ solution for 10 min. The resulting chemically modified electrodes were electrochemically characterized toward the oxidation of amino compounds in carbonate solutions buffered at pH 10. Under chronoamperometric experiments carried out at a constant applied potential of 0.95 V vs SCE, the linear range (r ²>0.995) was determined to be at least three decades and the limit of detection range from 26M (ethylamine) and 65M (tert-butylamine), for the investigated amino compounds. The perm-selective properties of the Nafion^® film with respect to anion species were investigated toward the electrooxidation of ethylamine in presence of large concentration of chloride ions. The XPS analysis revealed heterogeneous distribution of the catalytic species dispersed in the metalized Nafion^® film. Thus, a comparison of the spectra of Ag3d and Pb4f acquired at various take-off angles, indicates an increase in the atomic ratio Ag:Pb and a notable enrichment of lead oxide species in the outer surface of the film when compared with the bulk membrane coated electrode.     

Electrocatalytic Oxidation of Hydrogen Peroxide by Poly(NiIIteta) modified Electrodes§

[Ni^II(teta)]²⁺ (teta=C-meso-(5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane) was electropolymerized on glassy carbon (GC) and Nafion^® coated GC electrodes (GC/Nf). These poly(Ni^IIteta) modified electrodes showed 70 mV shift per pH unit and electrocatalysed the oxidation of H₂O₂. The thickness of the Nafion^® film was found to influence the rate of the electrocatalytic reaction. A rate constant of 1.77 × 10³ dm³ mol^–1 s^–1 was observed at 1.0 × 10^–5 cm thick Nafion^® film, whereas a rate constant of 0.08 × 10³ dm³ mol^–1 s^–1 was observed at 3.6 × 10^–5 cm thick film. At a plain GC electrode, a rate constant of 1.29 × 10³ dm³ mol^–1 s^–1 was observed. The poly(Ni^IIteta) is stabilized in the Nafion^® film when compared to the poly(Ni^IIteta) coated on plain electrode.     

Structure characterisation and mechanical properties of crystalline alumina coatings on stainless steel fabricated via sol–gel technology and fibre laser processing

The surface modification of stainless steel by coating with alumina (Al₂O₃) was carried out using sol–gel coating technology in combination with laser processing. Alumina coatings have been synthesised via a sol–gel route and deposited on stainless steel substrates by dip coating. The coated substrates were then treated with pulsed ytterbium fibre laser radiation (λ = 1064 nm) in continuous wave mode with different specific energies. The composition and structure of the coated surfaces after laser processing were characterised by ATR-FTIR, XRD, SEM and contact angle measurements, whilst the mechanical properties of modified surfaces were determined using nano-indentation. The results showed that the alumina xerogel films coated on the substrates are successfully converted into crystalline alumina ceramic coatings by the laser irradiation, the structure of resulting coatings being dependent on the irradiation conditions, with increase of laser specific energy leading to the formation of initially γ-Al₂O₃ with increasing amounts of α-Al₂O₃ at higher energy. Nano-indentation results reveal that the laser processing results in significant improvement in hardness and Young's modulus of the alumina-coated surface and, at optimum, can achieve the mechanical properties at the same level as pure α-alumina ceramic, much higher than those of the as-dried xerogel coating.     

Investigation of anti-corrosion behavior of waterborne organosilane–polyester coatings for AA6011 aluminum alloy

Thermal-cured, sol–gel derived, waterborne organosilane–polyester coatings (SiE) have been developed using methyltrimethoxysilane, 3-glycidoxytrimethoxysilane and polyester resin for corrosion protection of aluminum AA6011. The structural and morphological features of the coatings were analyzed by Fourier transform infrared spectroscopy (FT-IR) and atomic force microscopy (AFM). Results show that the coatings on aluminum were smooth, continuous and defect-free. Performance of the SiE coatings were investigated and compared with pure organosilane coating and polyester coating using potentiodynamic polarization studies, contact angle measurement and pencil hardness test. Results from polarization studies have shown that the SiE coated substrate (4.6–13.1 × 10⁻⁷ A/cm²) provided a better corrosion protection than the polyester coated substrate (7.8 × 10⁻⁶ A/cm²) due formation of aluminum–oxygen–silicon covalent bond at aluminum-coating interface. Furthermore, SiE coatings provided better hydrophobicity and hardness than the polyester coating.     

Corrosion inhibition by Nafion-polyaniline composite films deposited on stainless steel in a two-step process

The inhibition of pitting corrosion of stainless steel (SS) is addressed in this paper by using a new type of anticorrosive coatings consisting of Nafion^®-polyaniline (PAn) composite films electrodeposited on stainless steel in a two-step process. The anticorrosive strategy presented here is based on the interfacial modification of SS with a Nafion^® film, which as a cationic selective membrane prevents chloride ions to reach the SS surface. In addition, chloride insertion to the composite Nafion^®-PAn film becomes less likely since sulfonate groups of the Nafion^® contribute to the charge compensation of PAn and therefore charge transport processes involve proton expulsion than anion insertion. Nafion^® films were pre-deposited at the surface of the SS electrode and the PAn films were formed on the SS|Nafion^® electrode by cyclic voltammetry in 0.5 M H₂SO₄ solutions containing 0.1 M aniline. Open circuit potential and potentiodynamic measurements were used for the evaluation of the corrosion protection properties of the Nafion^®-PAn composites.     

Influence of bias voltage on diamond like carbon (DLC) film deposited on polyethylene terephthalate (PET) film surfaces using PECVD and its blood compatibility

In this paper, diamond like carbon (DLC) films were coated on polyethylene terephthalate (PET) film substrate as a function of biasing voltage using plasma enhanced chemical vapour deposition. The surface morphology of the DLC films was analyzed by scanning electron microscopy and atomic force microscopy. The chemical state and structure of the films were analyzed by X-ray photoelectrons spectroscopy and Raman spectroscopy. The micro hardness of the DLC films was also studied. The surface energy of interfacial tension between the DLC and blood protein was investigated using contact angle measurements. In addition, the blood compatibility of the films was examined by in vitro tests. For a higher fraction of sp³ content, maximum hardness and surface smoothness of the DLC films were obtained at an optimized biasing potential of ? 300 V. The in vitro results showed that the blood compatibility of the DLC coated PET film surfaces got enhanced significantly.     

Electrooxidation of acetaldehyde on platinum-modified Ti/Ru0.3Ti0.7O2 electrodes

In this study, the electrochemical oxidation of acetaldehyde was investigated at activated massive DSA^® electrodes in acid medium, using differential electrochemical mass spectrometry (DEMS) and high-performance liquid chromatography (HPLC). The electrodes were prepared either by platinum electrodeposition or by depositing a highly nanodispersive-supported catalyst (Pt and Pt-Ni) over electrode surfaces with a Ti/Ru_0.3Ti_0.7O₂ nominal composition. Bulk electrolysis shows evidence of CO₂ and acetic acid formation. The electrocatalytic efficiency of the electrode material was also investigated as a function of the amount of catalyst added over the DSA^® electrode surface. The presence of RuO₂-active sites on the DSA^® substrate plays an important role in the reaction overall efficiency. The addition of platinum to DSA^® enhances the oxidation of acetaldehyde to CO₂. The role of the substrate on the direct activation of acetaldehyde oxidation is discussed on the basis of the direct application of the metal nanoparticle catalyst over conductive oxide surface based on Magneli phase (mixture of Ti_nO_2n−1 and other phases) from Ebonex^®.     

7-Octenyltrimethoxysilane,a model coupling molecule to study the adhesion promotion of a silicone elastomer on an Al 2024 alloy

Ultra-thin layers of 7-octenyltrimethoxysilane (7-OTMS) and of 7-OTMS mixed with n-octyltrimethoxysilane (n-OTMS) (1/1 and 1/10 v/v) have been prepared as adhesion primers for silicone coatings on mechanically polished AA2024 aluminum alloy. The characterization of the silane grafting has been carried out by X-ray photoelectron spectroscopy (XPS), polarization modulation-infrared reflection-adsorption spectroscopy (PM-IRRAS) and water contact angle measurements. Sylgard^®184 silicone has been spin-coated and cured on bare and modified aluminum to form 15 μm polymer films. Qualitative peel tests (ASTM D3359) and scanning electron microscopy (SEM) point to the beneficial effect of the 7-OTMS layer to the adhesion whereas mixed layers show comparatively poor adhesion.     

Structure–property correlation study of hyperbranched polyurethane–urea (HBPU) coatings

This paper deals with the structure–property relation of different HBPU coatings based on the variation of parameters like, NCO/OH ratio, generation number and type of diisocyanates used. For this, the NCO terminated HBPU prepolymers were synthesized first by reacting the different generation hyperbranched polyesters (HBPs) with excess diisocyanates. In the next step, these HBPU prepolymer coated films were completely moisture cured to get the desired HBPU coatings. The synthesized polymers were confirmed by ¹H, ¹³C NMR and FT-IR spectroscopy methods whereas structure–property relation was drawn from the FT-IR peak deconvolution technique. The degree of branching (DB) and percent composition of different structural units present in the HBPs were calculated from the ¹H and ¹³C NMR data by using Fretch equation. The melt viscosity study of different HBP samples suggests that most polyester sample showed Newtonian behavior. The coating film properties were studied by DMTA, TGA, UTM, and contact angle measurement instruments. DMTA and TGA data shows that the increase of NCO/OH ratio and generation number had a favorable impact on storage modulus (E′), glass transition temperature (T_g), onset degradation temperature (T_1ON) and char residue values of the coatings. The contact angle and UTM data suggest that the hydrophobicity and tensile strength increases but flexibility decreases with increasing the NCO/OH ratio.     

Encapsulation of cinnamaldehyde into nanostructured chitosan films

Recently, bioactive chitosan films featuring naturally derived essential oils have attracted much attention due to their intrinsic antimicrobial properties and applicability to a broad range of applications. Previously, the ability to form thick (t > 100 µm), chitosan‐essential oil films via solution casting has been demonstrated. However, the fabrication of well characterized ultrathin films (t < 200 nm) that contain essential oils remain unreported. Here, we systematically investigate increasing the incorporation of an essential oil, cinnamaldehyde (CIN) into ultrathin chitosan films. Films with and without the surfactant Span^®80 were spin‐coated. Qualitatively, films exhibited well‐defined structural color, which quantitatively ranged from 145 to 345 nm thick. Release studies confirmed that a 6× higher release of CIN was enabled by Span^®80 versus the chitosan control films, 30 µg versus 5 µg, respectively. These results suggest that nanostructured chitosan‐CIN coatings hold potential to delay bacterial colonization on a range of surfaces, from indwelling medical device to food processing surfaces. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41739.     

Proton conducting membranes based on semi-interpenetrating polymer network of Nafion and polybenzimidazole

A new strategy to prepare the reinforced composite membranes for polymer electrolyte membrane fuel cells (PEMFCs), which can work both in humidified and anhydrous state, was proposed via constructing semi-interpenetrating polymer network (semi-IPN) structure from polybenzimidazole (PBI) and Nafion^®212, with N-vinylimidazole as the crosslinker. The crosslinkable PBI was synthesized from poly(2,2′-(m-phenylene)-5,5′-bibenzimidazole) and p-vinylbenzyl chloride. The semi-IPN structure was formed during the membrane preparation. The composite membranes exhibit excellent thermal stability, high-dimensional stability, and significantly improved mechanical properties compared with Nafion^®212. The proton transport in the hydrated composite membranes is mainly contributed by the vehicle mechanism, with proton conductivity from ∼10⁻² S/cm to ∼10⁻¹ S/cm. When the temperature exceeds 100 °C, the proton conductivity of the semi-IPN membranes decreases quickly due to the dehydration of the membranes. Under anhydrous condition, the proton conductivity of the membranes will drop to ∼10⁻⁴ S/cm, which is also useful for intermediate temperature (100-200 °C) PEMFCs. The benzimidazole structure of PBI and the acidic component of Nafion^® provide the possibility for the proton mobility via structure diffusion involving proton transfer between the heterocycles with a corresponding reorganization of the hydrogen bonded network.     

New performance of a modified poly(amide-12-b-ethyleneoxide)

The purpose of this work was the investigation of the water vapour transport through thermoplastic dense films of a poly(amide-12-b-ethylenoxide) such as Pebax^®2533. Similar polymers have gained a unique position in many technologies for different reasons, such as their good physical properties, high processability, notable strength and transport properties to gases and vapours. Moreover, a rising demand of materials with specific characteristics in terms of water vapour transport comes from various market niches (i.e. textiles, building trade, packaging). For these reasons in this work particular attention has been paid to an elastomeric polymer such as the Pebax^®2533, an easily processable material with good transport properties. Previous studies have pointed out that Pebax^® copolymers can be used as precursors of membranes for separation processes of condensable vapours and gases. In this work a further investigation of the water transport properties through Pebax^®2533 and derivative films allowed an understanding of their potential applications. The efficiency of these films has been tested by means of vapour permeability, solubility, diffusivity, and hydrophobicity/hydrophilicity measurements.     

Hybrid sol–gel coatings for corrosion protection of galvanized steel in simulated concrete pore solution

The aim of this experimental research was to study the electrochemical behavior of organic–inorganic hybrid (OIH) coatings for corrosion protection of hot-dip galvanized steel (HDGS) in the first instants of immersion in simulated concrete pore solution (SCPS) (pH > 12.5). The electrochemical performance of the OIH coatings was assessed by electrochemical impedance spectroscopy, potentiodynamic polarization curves, macrocell current density, and polarization resistance. The OIH coatings were prepared via the sol–gel method and were deposited on HDGS surfaces by dip-coating using one or three dip steps. The electrochemical results obtained for HDGS samples coated with OIH matrices in SCPS showed higher corrosion resistance than bare HDGS; as the molecular weight (MW) of Jeffamine^® increased the barrier protection of the coating decreased. The lowest protection efficiency was found for HDGS samples synthesized with oligopolymers with an MW of 2000. Coatings produced with an oligopolymer of 230 MW conferred the highest protection. The surface morphology of the OIH coatings deposited on HDGS surfaces was studied by atomic force microscopy. The results show that the roughness of the OIH films depends on the MW of Jeffamine^® and on the number of dip-coating steps used. Thermogravimetry results show that the Jeffamine^® MW affected the thermal properties of the prepared OIH samples. The prepared OIH materials are thermally stable within the range of 20–80°C.     

Response of 45S5 Bioglass foams to tensile loading

The tensile strength test of highly porous ceramic foams has been developed and first results have been obtained on bioactive glass foams. The tested material was a 45S5 Bioglass^® derived foam-like scaffold intended for use in bone tissue engineering which was manufactured by Bioglass^® slurry coating of polyurethane foam and subsequent sintering. The Bioglass^® foam structure was investigated in two states: uncoated (as fabricated) and with a PDLLA polymer coating. The tensile testing procedure is based on fixation of the foam into aluminium pots by a suitable adhesive. Tensile test samples having cross-section of 10×10 mm² and a length of 30 mm were used for the experiments. Basic fractographic analysis was applied to get relevant information about specimens' behaviour during tensile loading. In Bioglass^® based scaffolds, the presence of PDLLA coating led to a significant increase of the fracture strength, which is attributed to the interaction of the polymer phase with propagating cracks, e.g. enabling a crack bridging mechanism to take place.     

Crystallisation of Foturan glass-ceramics

Photostructurable glass-ceramics are suitable for 3-dimensional microfabrication and, in some instances, can be used as an alternative material to silicon in the microfabrication of micro-electro-mechanical-system (MEMS) devices. Foturan^® is a photosensitive lithium-aluminium-silicate glass that can be structured by an exposure to UV light, followed by a thermal treatment and an etching step. In this work, the crystallisation kinetics and microstructure evolution of unexposed and UV-exposed Foturan^® are investigated by means of differential scanning calorimetry, X-ray diffraction and scanning electron microscopy. The glass transition temperature T_g, the apparent activation energy of crystallisation E_a and the colour of UV-exposed Foturan^® are discussed. It is shown that nucleation and crystallisation of UV-exposed Foturan^® can be steered either as a function of temperature (non-isothermal) or as a function of time (isothermal). This is essential for the photostructuring and etching of Foturan^® regarding the achievable feature sizes of 25 μm for MEMS applications.     

Stretchable conductive films based on carbon nanomaterials prepared by spray coating

Stretchable conductive films consisting of a layer of carbon nanomaterials, that is, carbon nanotubes (CNTs), mechanically exfoliated graphene (GE), or chemically reduced graphene oxide (rGO), deposited on polydimethylsiloxane (PDMS) films were prepared by spray coating. The correlations among the concentration of the carbon nanomaterials, the electrical resistance and the optical transmittance of the spray‐coated films were investigated. The results show that the conductivity of the CNT coatings was better than that of the GE‐based coatings. When the CNT concentration of the dispersion for spraying increased from 0.01 to 0.075 mg/mL, the surface electrical resistance decreased from 7.8 × 10³ to 6.7 × 10² Ω, whereas for the GE or rGO coatings, the electrical resistance was several orders higher than that of the CNT coatings. The CNT spray‐coated films exhibited an optical transmittance of about 60% at a wavelength of 550 nm; this was higher than that of the GE or rGO spray‐coated films. The electric heating behaviors of the stretchable conductive films as functions of the applied voltage and the concentration of carbon nanomaterials and the electrical conductivity under tensile and bending strains were also investigated. The surface temperature of the CNT‐coated films rose rapidly up to 200°C within about 40 s when the applied voltage was 110 V. The stretchable conductive films have potential as electric heating elements because of their excellent conductive properties. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43243.     

Kevlar-functionalized graphene nanoribbon for polymer reinforcement

Multiwalled carbon nanotubes (MWCNTs) have been widely used as reinforcement fillers in past decades. However, the reinforcement effect has been greatly hindered by the limited available interface area (AIA) with polymer matrices for polymer composites. Successively, the method of oxidative unzipping MWCNTs into graphene nanoribbons (GNRs) was demonstrated to be the effective way for addressing the inherent drawback of MWCNTs. However, the GNRs are easy to agglomerate in polymer matrix even at relatively low loading amount. In this paper, we found that the functionalization of GNRs with Kevlar^® can significantly improve the dispersion state of GNRs in polymer matrix. Consequently, Kevlar^®-functionalized graphene nanoribbons (KGNRs) were successfully prepared through non-covalent functionalization of π–π stacking interaction between the aromatic area of Kevlar^® and the graphitic surface of GNRs. As-prepared KGNRs were characterized by FT-IR, TGA, XRD and TEM measurements. Poly(vinyl chloride) (PVC) and poly(methyl methacrylate) (PMMA) were selected as model polymers to investigate the reinforcement effect of KGNRs. The KGNRs could be well dispersed in PVC and PMMA matrices at relatively high loading level. Meantime, the ultimate tensile strengths and Young's modulus of KGNRs/PVC and KGNRs/PMMA composite films were significantly improved. Based on the observations above, KGNRs hold great promise in many potential applications in the future.