Dip-coating Procedure Research Articles

Dextran-Thyme Magnesium-Doped Hydroxyapatite Composite Antimicrobial Coatings

The dextran-thyme magnesium-doped hydroxyapatite (10MgHAp-Dex-thyme) composite layers were prepared by a dip-coating procedure from stable suspensions and further analyzed for the first time. Different characterization techniques were employed to explore the physical-chemical features of the 10MgHAp-Dex-thyme suspensions and derived coatings. Information regarding the 10MgHAp-Dex-thyme suspensions was extracted on the basis of dynamic light scattering, zeta potential, and ultrasound measurements. The crystalline quality of the biocomposite powders—resulting after the centrifugation of suspensions—and the layers deposited on glass was assessed by X-ray diffraction in symmetric and grazing incidence geometries, respectively. The chemical structure and presence of functional groups were evaluated for both powder and coating by Fourier transform infrared spectroscopy in attenuated total reflectance mode. The extent of the antimicrobial effect range of the biocomposite suspensions and coatings was tested against different Gram-positive and Gram-negative bacteria (Staphylococcus aureus, Enterococcus faecalis, Escherichia coli, and Pseudomonas aeruginosa) and fungus (Candida albicans) strains with promising results.

Improving Performance of Fibriform Supercapacitor Based on Cotton Thread by Uncoiling Dip-Coating Procedure

Fibriform supercapacitor (FSC) based on cotton thread (CT) produced by dip-coating presents great potential in wearable electronics. However, active materials especially for reduced graphene oxide (RGO) sheets tend to restack on the surface of CT and are difficult to permeate into the inside of CT, thus fading performance. In this work, each cotton yarn (CY) obtained by uncoiling CT is uniformly covered by GO (GO-CY) and RGO coated CT (RGO-UCDCT) is obtained through twisting these GOCYs, followed by subsequent reduction. Uncoiling dip-coating alleviates the restacking of RGO sheets on the surface of CT. Thus, the FSC based on RGO-UCDCTs exhibits superior performance including high volumetric capacitance of 1.85 mF cm-3 and good rate capability. The findings provide a cost-effective procedure of uncoiling dip-coating for improving performance of CT based FSC.

Combined dip-coating/spin-coating depositions on ceramic honeycomb monoliths for structured catalysts preparation

This work focuses on the investigation of a combined dip-coating/spin-coating technique as novel deposition procedure for structured catalysts production; it consists in the use of a spin-coater device to remove the excess slurry entrapped in structured supports porosity after the dip-coating procedure, by centrifugation. In particular, ceramic monoliths (500 cells per square inch, diameter 1 cm, length 1.5 cm) were chosen as a model support and cerium oxide as a catalyst carrier. The support was selected based on its potential in the syngas production field. A preliminary analysis of the deposition conditions was performed by using water/glycerol solutions of various compositions to investigate a broad range of model liquid viscosities. The influence of coating parameters, such as rotation speed and rotation time, on coating thickness was assessed and optimal conditions for washcoat deposition were identified. Then, a cerium oxide carrier layer was deposited by means of slurry coating route. In particular, an acid-free formulation based on water, glycerol and polyvinyl alcohol was used as liquid medium for the ceramic particles dispersion. Washcoat loads in the 10 wt.% range were obtained after four consecutive depositions. Results were evaluated in terms of coating load and adhesion performance. Moreover, a comparison with similar samples obtained by solely using dip-coating was carried out. Washcoat layers of 11 and 5 μm were found for dip-coated and spin-coated samples, respectively. Additionally, the use of spin coating allowed an improvement in both results reproducibility and washcoat adhesion.

Honeycomb Structured Catalysts for H2 Production via H2S Oxidative Decomposition

Cordierite honeycomb structured catalysts were studied for the reaction of H2S decomposition in the presence of oxygen to obtain H2 and sulphur. An Al2O3-based washcoat was deposited on the honeycomb monolith by a dip-coating procedure. In particular, three different washcoat percentages (15, 20 and 30 wt%) were deposited on the structured carrier and the obtained samples were characterized by N2 adsorption and SEM analysis. The evaluation of the catalytic performance of the three samples was carried out at two different temperatures (1000 °C and 1100 °C). The sample with 30 wt% washcoat content showed the lowest SO2 selectivity at 1000 °C (<0.4%), whereas the H2S conversion and H2 yield values were very similar to those achieved for the samples at 15 and 20 wt% washcoat loading. Based on these results, additional tests were carried out on the catalyst with 30 wt% Al2O3-based washcoat loading, varying the contact time and the H2S inlet concentration to identify the operating conditions that minimize the SO2 formation, obtaining good H2S conversion and H2 yield. The comparison of the structured catalyst with the powder alumina sample has shown the same catalytic performance, exhibiting lower SO2 selectivity.

Ultralow Fouling Surfaces from Self-Assembly of Copolymers with Sticky Biomimic Functional Groups

In this work, a new strategy for preparing antifouling surfaces by a simple dip-coating procedure is reported. Copolymers containing catechol and antifouling pendant side groups were synthesized via the free radical polymerization of a catechol-containing methacrylate monomer N-(3,4-dihydroxyphenyl) ethyl methacrylamide and three kinds of antifouling monomers separately using α,α’-azobisisobutyronitrile (AIBN) as initiator. These copolymers can assemble onto variety of materials surfaces including metals, oxides, and polymers such as PTFE using catechol groups via multivalent complex bonding. The catechol groups are helpful for adhesion of the copolymers onto the surfaces, while the other side chains endow the coatings with antifouling activity. Modification on the substrates with copolymers were verified by X-ray photoelectron spectroscopy (XPS), the images of microalgaes and zoospores setting on the substrates were taken by microscope and scanning electron microscope (SEM). The copolymer-coated surfaces, especially the surface modified by copolymer with 3-sulfopropyl methacrylate potassium salt (SPMA(K)), displayed excellent antifouling activity and fouling-release properties in settlement assay with microalgaes and zoospores.

Layer-by-layer assembly of iron oxide-decorated few-layer graphene/PANI:PSS composite films for high performance supercapacitors operating in neutral aqueous electrolytes

The layer-by-layer assembly of polyaniline-PSS (PANI:PSS) complexes and iron oxide nanoparticles-decorated few-layer graphene (Fe-FLG) from aqueous dispersions, yielding an electrode material with excellent electrochemical capacitive performance in simple neutral aqueous electrolyte is presented. The simple dip-coating procedure allows the effective incorporation of both materials and the control of the film nanoarchitectonics. The resulting composite coating was characterized by XPS and Raman spectroscopies. A linear dependence of the capacitance on the film mass indicates that both building blocks are efficiently (and electrochemically) connected within the films. The electrochemical performance of the film-coated electrodes was tested in both acidic (0.1 M HCl) and neutral (0.1 M KCl) aqueous electrolytes. Electrodes constituted of 15 self-assembled bilayers showed the best performance with a high capacitance of 768.6 F g−1 and 659.2 F g−1 in 0.1 M HCl and 0.1 M KCl, respectively, at the current density of 1 A g−1. Moreover, a high stability to continuous cycling was observed, even in aqueous neutral solution (86% capacitance retention after 1600 cycles at 3 A g−1). This ternary material then constitutes a promising candidate for the construction of environmentally friendly supercapacitors.

Bioinert Control of Zwitterionic Poly(ethylene terephtalate) Fibrous Membranes.

Poly(ethylene terephtalate) (PET)-based materials face general biofouling issues that we addressed by grafting a copolymer of glycidyl methacrylate and sulfobetaine methacrylate, poly(GMA- r-SBMA). The grafting procedure involved a dip-coating step followed by UV-exposure and led to successful grafting of the copolymer as evidenced by X-ray photoelectron spectroscopy and zeta potential measurements. It did not modify the pore size nor the porosity of the PET membranes. In addition, their surface hydrophilicity was considerably improved, with a water contact angle falling to 30° in less than 20 s and 0° in less than 1 min. The effect of copolymer concentration in the coating bath (dip-coating procedure) and UV exposure time (UV step) were scrutinized during biofouling studies involving several bacteria such as Escherichia coli and Stenotrophomonas maltophilia, but also whole blood and HT1080 fibroblasts cells. The results indicate that if all conditions led to improved biofouling mitigation, due to the efficiency of the zwitterionic copolymer and grafting procedure, a higher concentration (15 mg/mL) and longer UV exposure time (at least 10 min) enhanced the grafting density which reflected on the biofouling results and permitted a better general biofouling control regardless of the nature of the biofoulant (bacteria, blood cells, fibroblasts).

Gas permeation properties of a metallic ion-cross-linked PIM-1 thin-film composite membrane supported on a UV-cross-linked porous substrate

Abstract Metallic ion-cross-linked polymer of intrinsic microporosity (PIM-1) thin-film composite (TFC) membranes supported on an ultraviolet (UV)-cross-linked porous substrate were fabricated. The UV-cross-linked porous substrate was prepared via polymerization-induced phase separation. The PIM-1 TFC membranes were fabricated via a dip-coating procedure. Metallic ion-cross-linked PIM-1 TFC membranes were fabricated by hydrolyzing the PIM-1 TFC membrane in an alkali solution and then cross-linking it in a multivalent metallic ion solution. The pore size and porous structures were evaluated by low-temperature N2 adsorption–desorption analysis. The membrane structure was investigated by field-emission scanning electron microscopy. The effects of heat treatment and pore-forming additives on the gas permeance of the UV-cross-linked porous substrate are reported. The effects of different pre-coating treatments on the gas permeance of the metallic ion-cross-linked PIM-1 TFC membrane are also discussed. The metallic ion-cross-linked PIM-1 TFC membrane displayed high CO2/N2 selectivity (23) and good CO2 permeance (1058 GPU).

Engineering Nitroxide Functional Surfaces Using Bioinspired Adhesion.

We pioneer a versatile surface modification strategy based on mussel-inspired oxidative catecholamine polymerization for the design of nitroxide-containing thin polymer films. A 3,4-dihydroxy-l-phenylalanine (l-DOPA) monomer equipped with a 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-derived oxidation-labile hydroxylamine functional group is employed as a universal coating agent to generate polymer scaffolds with persistent radical character. Various types of materials including silicon, titanium, ceramic alumina, and inert poly(tetrafluoroethylene) (PTFE) were successfully coated with poly(DOPA-TEMPO) thin films in a one-step dip-coating procedure under aerobic, slightly alkaline (pH 8.5) conditions. Steadily growing polymer films (∼1.1 nm h-1) were monitored by ellipsometry, and their thicknesses were critically compared with those obtained from atomic force microscopic cross-sectional profiles. The heterogeneous composition of surface-adherent nitroxide scaffolds examined by X-ray photoelectron spectroscopy was correlated to that examined by in-solution polymer analysis via high-resolution electrospray ionization mass spectrometry, revealing oligomeric structures with up to six repeating units, mainly composed of covalently linked dihydroxyindole along the polymer backbone. Critically, the reversible redox-active character of the nitroxide-containing polymer scaffolds was investigated by cyclic voltammetric measurements, revealing a convenient and facile access route to electrochemically active nitroxide polymer coatings with potential application in electronic devices such as organic radical batteries.

LSPR based optical fiber sensors treated with nanosecond laser irradiation for refractive index sensing

This article reports on the application of localized surface plasmon resonance (LSPR) based optical fiber probes in the form of U-shape geometry, as refraction index (RI) sensors in sucrose and alcohol solutions. For their fabrication, the immobilization of gold nanoparticles (AuNP) on the probe’s active area was achieved by a dip-coating procedure and the formed AuNP decoration was tailored by ns laser irradiation at 532nm. The procedure was monitored and controlled in real time by recording the induced changes into the optical fiber extinction spectra. For the optimization of the fabrication technique, an irradiation protocol is established while the dependence of RI sensitivity on the AuNP size and their abundance on the fiber have been explored. Sensors with RI sensitivities, comparable to the best reported in the literature (up to ΔΕ/ΔRI=45.2) were developed from mono-dispersed colloidal solutions of AuNP. Finally, it should be stressed that following the same procedure, sensors with similar RI sensitivity (ΔΕ/ΔRI=33.9) were fabricated by using a mixture of different size (20–100nm) AuNP bypassing the necessity of mono-dispersed solutions.

A facile and scalable coating technique of carbon fibers with carbon nanoparticles for surface adhesion enhancement of fibers and resin in 2D C/C composites

Abstract In order to improve mechanical properties of 2D carbon-carbon composite via increasing fiber/matrix interfacial adhesion, we have developed a simple, low cost and scalable method for carbon fibers (CFs) coating. This method is inspired to ink printing process in which pigments/dyes are transferred and set on the different surfaces via proper chemical bindings. For this purpose, we have used colloidal suspension of carbon nanoparticles in printing ink solution and coated the surfaces through dip-coating procedure. The results of SEM observations showed that colloidal suspension of nano-carbon particles in ink solution could be successfully used as a coating solution for preparing a uniform, well distributed and defect-free coating. Also water wettability measurement test has been conducted in order to evaluate the carbon coating on the surface chemistry of carbon nanofibers. The results revealed significant improvement on wettability of CFs after coating owing to abundant hydrophilic groups introduced from ink solution onto the surface of CFs (approved by FTIR spectroscopy). Finally, the mechanical properties of 2D C/C composites prepared by as-received and nano-coated CFs have been evaluated. The result of mechanical properties showed remarkable improvement in both flexural and shear strength of final composite by 15% and 18%, respectively.

Sol–gel processing of calcium hydroxyapatite thin films on silicon nitride (Si3N4) substrate

Calcium hydroxyapatite (Ca10(PO4)6(OH)2, CHAp) films were obtained on silicon nitride (Si3N4) substrate by a sol–gel method using a dip-coating technique. In the sol–gel process, ethylendiamintetraacetic acid and 1,2-ethandiol, triethanolamine, and polyvinyl alcohol were used as complexing agents and gel network forming agents, respectively. Calcium acetate monohydrate was used as Ca source. The samples were annealed at 650 °C for 5 h in air after each dip-coating procedure which was repeated 10, 20, and 30 times. The coatings were characterized using X-ray diffraction, scanning electron microscopy, atomic force microscopy, Raman spectroscopy, and contact angle measurements. Monophasic CHAp layers on silicon nitride (Si3N4) substrate were fabricated and characterized for the first time to the best our knowledge.

In-VitroDevelopment and Characterisation of a Superoxide Dismutase-Based Biosensor.

A first generation amperometric biosensor for the detection of superoxide (O2−) was constructed utilising a dip-coating approach for immobilising the enzyme superoxide dismutase (SOD, 200 U/mL) onto a Pt electrode. Several dip-coating procedures were investigated, incorporating styrene, glutaraldehyde, bovine serum albumin and polyethylenimine at various concentrations, in order to develop a simple and reproducible coating method to maximise the sensitivity of the sensor to O2−. The optimised design was produced using 5 dip-coatings and a composite containing 200 U/mL SOD, 0.5 % glutaraldehyde and 2 % polyethylenimine (Sty-(SOD-0.5 %GA-2 %PEI)5). This sensor displayed excellent permselective characteristics with negligible signals produced by 12 of the most common electroactive species present in brain extracellular fluid, including uric acid (UA) which is produced as a by-product of the O2− generating xanthine-xanthine oxidase calibration method. In addition, it had a response time of ca. 1 s, high sensitivity to O2− (0.91 ± 0.02 nA/μM), and an in-vitro limit of detection of ca. 0.063 μM, thus suggesting potential use for neurochemical monitoring of O2− in-vivo.

The reinforcing effect of polydopamine functionalized graphene nanoplatelets on the mechanical properties of epoxy resins at cryogenic temperature

In order to obtain epoxy nanocomposites with excellent mechanical properties at cryogenic temperature, an efficient method to functionalize graphene nanoplatelets (GNPs) is proposed. Through a simple dip-coating procedure, the GNPs were first functionalized with deposition of polydopamine coating (PDA@GNPs). Then, using polydopamine as a bridge, the PDA@GNPs were modified with amine groups after polyetheramine T403 grafting (T403-PDA@GNPs). Fourier transform infrared spectroscopy, thermogravimetric analysis and X-ray photoelectron spectroscopy analyses proved the successful functionalization of PDA and polyetheramine T403 on the surface of GNPs. Adding 0.1 wt% T403-PDA@GNPs significantly improved the cryogenic tensile strength and impact strength of the epoxy nanocomposites by 34.5% and 64.5%, which showed greater reinforcing effect than the pristine GNPs (12.6% and 19.1%) and PDA@GNPs (26.3% and 50.1%). The results of dynamic mechanical analysis and scanning electron microscopy observations indicated that the PDA and further polyetheramine T403 functionalization improved the interfacial interactions between GNPs and matrix, which ensured the much improved mechanical properties.

Surface Modification of Aramid Fibers by Catechol/Polyamine Codeposition Followed by Silane Grafting for Enhanced Interfacial Adhesion to Rubber Matrix

In this work, we develop a modified mussel-inspired method to enhance interfacial adhesion of aramid fiber to a rubber matrix. Through a simple dip-coating procedure, catechol and polyamine could initially codeposit as a poly(catechol-polyamine) (PCPA) coating on the surface of the aramid fiber. Then, the PCPA layer could be further grafted with silane coupling agent γ-(glycidyloxypropyltrimethoxysilane) (GPTMS). Results indicated that GPTMS was successfully grafted onto the aramid fiber surface via the bridging of the PCPA layer. The interfacial adhesion between the aramid fibers and the rubber matrix was improved compared to that achieved by polydopamine in our previous study. In addition, this method is more applicable to the rubber industry than polydopamine coating because of its cost-effectiveness and short reaction time.

Development of fluorescent thermoresponsive nanoparticles for temperature monitoring on membrane surfaces

In this work, tris(phenantroline)ruthenium(II) chloride (Ru(phen)3) was immobilized in silica nanoparticles prepared according to the Stöber method. Efforts were devoted on the optimization of the nano-thermometer in terms of size, polydispersity, intensity of the emission and temperature sensitivity. In particular, the immobilization of the luminophore in an external thin shell made of silica grown in a second step on bare silica nanoparticles allowed producing fluorescent monodisperse silica nanoparticles (420±20nm). A systematic study was addressed to maximize the intensity of the emission of the fluorescent nanoparticles by adjusting the concentration of Ru(phen)32+ in the shell from 0.2 to 24wt.%, whereas the thickness of the shell is affected by the amount of silica precursor employed.The luminescent activity of the doped nanoparticles was found to be sensitive to the temperature. In fact, the intensity of the emission linearly decreased by increasing the temperature from 20°C to 65°C. The thermoresponsive nanoparticles were functionalized with long aliphatic chains in order to obtain hydrophobic nanoparticles. The developed nanoparticles were immobilized via dip-coating procedure on the surface of hydrophobic porous membranes, such as Polyvinylidene fluoride (PVDF) prepared via Non-Solvent Induced Phase Separation (NIPS), providing local information about the membrane surface temperature.

Use of an electrochemical room temperature ionic liquid-based microprobe for measurements in gaseous atmospheres

A simple electrochemical microprobe (EMP) is proposed for the detection of analytes in gaseous atmospheres. The EMP consists of two platinum fibres of 25 and 300μm in diameter encased into a theta glass pipette to form an electrochemical cell in a two-electrode configuration. Ion conductivity between the two electrodes is ensured by a thin film of the room temperature ionic liquid (RTIL), 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, which is applied onto the EMP tip surface by a simple dip-coating procedure. The ionic liquid-coated microprobe (RTIL-EMP) was preliminarily investigated by using ferrocene as an electroactive species to ascertain the mass transport properties of the analytes that influence the voltammetric responses as well as the stability and reproducibility of the RTIL-EMP in the gas phase. The performance of the RTIL-EMP to gas analysis was afterward evaluated by using oxygen as electroactive species. The RTIL-EMP was exposed to different synthetic O2/N2 (v/v) mixtures and current responses were recorded as a function of O2 concentration, using either cyclic voltammetry (CV) or chronoamperometry (CA). Regression analysis of the experimental current against % O2 was linear over the range 0–100% with correlation coefficient and sensitivity of, respectively, 0.996 and 0.29nA/(v/v) % O2 in CV and 0.998 and 0.27nA/(v/v) % O2 in CA measurements. Long term stability, reproducibility of the RTIL-EMP recovery of the RTIL film layers to the initial conditions and effects of humidity on the current responses were investigated in detail.

Poly(polyol sebacate) Elastomers as Coatings for Metallic Coronary Stents

Biocompatible polymeric coatings for metallic stents are desired, as currently used materials present limitations such as deformation during degradation and exponential loss of mechanical properties after implantation. These concerns, together with the present risks of the drug-eluting stents, namely, thrombosis and restenosis, require new materials to be studied. For this purpose, novel poly(polyol sebacate)-derived polymers are investigated as coatings for metallic stents. All pre-polymers reveal a low molecular weight between 3000 and 18 000 g mol-1 . The cured polymers range from flexible to more rigid, with E-modulus between 0.6 and 3.8 MPa. Their advantages include straightforward synthesis, biodegradability, easy processing through different scaffolding techniques, and easy transfer to industrial production. Furthermore, electrospraying and dip-coating procedures are used as proof-of-concept to create coatings on metallic stents. Biocompatibility tests using adipose stem cells lead to promising results for the use of these materials as coatings for metallic coronary stents.

Synergistic photoelectrochemical reduction of Cr(VI) and oxidation of organic pollutants by g-C3N4/TiO2-NTs electrodes

The g-C3N4/TiO2-NTs electrodes were synthesized by a dip-coating procedure followed by high-temperature annealing used in photoelectrochemical process. From the results, a simultaneous and rapid reduction of Cr(VI) and degradation of phenol in Cr(VI)/phenol system was observed with photoelectrocatalytic activity under UV–visible light irradiation than photocatalytic and electrocatalytic activities. The different kinds of Cr(VI)/organic pollutants systems were also investigated systematically. In addition, different scavengers were also added in Cr(VI)/phenol and Cr(VI)/benzyl alcohol systems to indicate that the hydroxyl radicals and superoxide radicals were the most major active species for the denomination of Cr(VI) and organic pollutants. The intermediates of phenol and benzyl alcohol were also detected during the reaction in order to deduce the photoelectrocatalysis mechanism underg-C3N4/TiO2-NTs electrodes that the charge separation was improved and subsequently electron-transfer efficiency was higher.

Tailored Aggregate-Free Au Nanoparticle Decorations with Sharp Plasmonic Peaks on a U-Type Optical Fiber Sensor by Nanosecond Laser Irradiation

A novel experimental methodology is presented for fabricating U-shaped optical fiber probes decorated with aggregate-free Au nanoparticles exhibiting sharp localized surface plasmon resonance (LSPR) spectra. The U-type tip is coated with gold nanoparticles (AuNPs) using a simple and time-efficient dip-coating procedure, without initially taking any care to prevent the formation of nanoparticle aggregates in the coated area. In a second step, the coating was irradiated with a few tens of laser pulses of 5-ns duration at 532 nm with intensities in the range of 2–14 MW/cm2, leading to the formation of aggregate-free LSPR optical fiber probes. The process was monitored and controlled in real time through the changes induced into the fiber’s extinction spectra by the laser irradiation, and the coated fibers were characterized by electron microscopy. The proposed methodology resulted into the fabrication of U-type optical fiber probes coated with AuNPs exhibiting a sharp plasmon peak, which is a perquisite for their application as sensing devices.