Spray-coating Technique Research Articles

Spectral Imaging of UV-Blocking Carbon Dot-Based Coatings for Food Packaging Applications

Nowadays, there is an increased demand to develop alternative non-plastic packaging to be used in the food industry. The most popular biodegradable films are cellulose and poly(lactic acid) (PLA); however, there is still the need to increase their UV absorption to protect the packaging content. In this work, we have covered those biodegradable films with thin coatings based on carbon dots (CDs) dispersed in polyvinyl alcohol (PVA) deposited by spin- or spray-coating techniques. We report a strong increase in the UV light-absorbing properties, together with a detailed morphological characterization; moreover, we show the results of a new microscopy and spectral imaging technique applied to the coated samples. The scientific and technological novelty of this approach is the possibility of characterizing large areas of the material surface by the simultaneous detection of PL spectra in all the pixels of a highly spatially-resolved two-dimensional (2D) map of the surface. We report UV-excited PL maps whose detailed information allows us to clearly identify regions with different spectral behaviors and to compare their characteristic signals for different CDs:PVA deposition techniques.

Single-walled carbon nanotube (SWCNT) thin film for optoelectronics device prepared by spray coating technique.

CNT is a novel material with exceptional properties. SWCNT thin films have been used in many different applications. To fabricate the SWCNT film, various methodologies have been introduced, however, the problem of fabricating uniform SWCNT thin film remains unsolved. Spray coating technique (SCT) is the most effective method for producing a uniform SWCNT thin film. The CNT thin films were deposited on glass substrates via SCT with different nozzle distances (from 2.5 cm to 12.5 cm). The morphological, topological, electrical and optical properties of CNT thin films were characterized using appropriate techniques. The electrical analysis depicted that the sheet resistance of thin films reduced from 40220 Ω/sq. to 1330 Ω/sq. as the spray nozzle distance was increased from 2.5 cm to 10 cm sheet resistance reached 2133 Ω/sq. for 12.5 cm which confirmed the concentration of CNT was highest at 10 cm nozzle distance. The optical analysis of the CNT thin films gave transmittance values in percentage of 64%, 60%, 52%, 43%, and 46%, respectively for the nozzle distance of 2.5 cm, 5 cm, 7.5 cm, 10 cm, and 12.5 cm. Transmittance percentage decreased from 2.5 cm to 10 cm nozzle distance, indicative of an uniform film coverage of CNT layer. The findings of this study could be a platform for producing an optimized CNT thin film using a SCT for optoelectronic devices.

Simple, Scalable Route to Produce Transparent Superhydrophobic/Hydrophilic Film Surfaces

Superhydrophobic coatings are gaining popularity because of their low maintenance requirements, high durability, and wide range of potential uses. Such coatings, for instance, may provide beneficial resistance to fouling, icing, smear, and corrosion, and can separate oil from water. Therefore, the creation of superhydrophobic materials is a topic of great interest to academics all around the world. In this paper, a spray-coating deposition technique is used to deposit silica nanoparticles on glass while using a sol–gel as a base. The applied coating increased the transmittance to 99% at 600 nm. Water contact angle (WCA) and scanning electron microscopy (SEM) observations of the coated layer’s grade index and induced porousness led to superhydrophobic behavior with a water contact angle that was higher than 158°.

Sustainable corrosion-resistant superhydrophobic composite coating with strengthened robustness

In this paper, a superhydrophobic composite coating was developed employing epoxy resin (EP), polydimethylsiloxane (PDMS), and hexadecyltrimethoxysilane (HDTMS) functionalized Al2O3 nanoparticles as raw materials through a versatile and easily-scalable spray-coating technique. The water contact angle (WCA) and sliding angle (SA) of the designed superhydrophobic composite coating were 154.1 ± 0.7°and 3.5 ± 0.3°, respectively. The superhydrophobic composite coating features Cassie-Baxter phase contact, liquids repellency, anti-fouling, and self-cleaning properties for various liquid and solid contaminants. Compared with bare Q235 carbon steel, the charge transfer resistance (Rct) value of superhydrophobic composite coating immersed in the 3.5 wt. % NaCl solution can be remarkably enhanced by more than 7 orders of magnitudes with a corrosion inhibition efficiency of 99.99%. The coating maintain its superhydrophobicity, ultra-low adhesion force, and sustainable corrosion resistance even suffering 150 tape-peeling and 80 abrasion cycles. The improved durable mechanical robustness and interfacial bonding force can be attributed to the cross-linked and polymerized three-dimensional network micro-nano hierarchical structures formed by the combination of EP, PDMS, and embedded Al2O3@HDTMS nanoparticles. Besides, the accelerated salt-spray corrosion test (480 h) and atmospheric corrosion exposure (100 days) of the coating demonstrated superior anti-corrosion performance in both laboratory and real-world corrosive environments.

Structure and Morphology of ZnO Films Co-Doped With Al and Rare Earth Deposited by Spray Coating Technique

"In this work, the influence of co-doping with Al and rare earth ions (RE= Er, Gd, Nd) on the structure and morphology of zinc oxide (ZnO) films is presented. Spray coated thin films were obtained using a mixture of nitrate substances diluted in equal quantities of distilled water and ethanol. The coated films were deposited on quartz glass and Si(100) substrates using a constant concentration of 0.15M, a temperature of 210ºC, pressure of 2 bar and 10 minutes time of deposition. After this step, the coated films were annealed at 3 different temperatures (600ºC, 800ºC and 1000ºC) for 5 minutes each. The influence of dopant and annealing treatment upon crystallographic structure of the films was analyzed by X-ray diffraction (XRD). Microstructural and surface analysis from scanning electron microscopy (SEM) and AFM measurements evidenced that the type of doping and the annealing treatment modify the surface morphology of the films. Keywords: spray coating technique, AZO-RE thin films, XRD, SEM, AFM. "

One-step spraying achieved superhydrophobic fluoroSiO2@epoxy coating with corrosion-wear resistance and anti-wetting stability

Biomimetic superhydrophobic materials with reduced liquid-solid interfacial contact, non-wetting and water repelling properties exhibits promising multi-functional application potentials, but hindered by poor mechanical stability, complex preparation process, expensive reagents, strict equipment requirements, and ecologically environmental pollution. Herein, we developed a corrosion resistant and mechanically stable superhydrophobic coating based on modified fluoroSiO2 and epoxy resin via a facile one-step spray-coating technique. The electrochemical impendence spectroscopy (EIS) and potentiodynamic polarization results confirmed the remarkably enhanced corrosion resistance of the superhydrophobic fluoroSiO2 @epoxy coating with a corrosion inhibition efficiency of 99.86%. More importantly, the created superhydrophobic fluoroSiO2 @epoxy coating maintains its non-wetting Cassie-Baxter state, self-cleaning and anti-fouling properties after continuously tape-peeling cycles, abrasion cycles, self-cleaning cycles and standard cross-cut tape tests, verifying a strengthened coating/substrate binding force and wear resistance. The easy adaptability and scalability of the spray-coating approach and mechanical robustness of the designed superhydrophobic fluoroSiO2 @epoxy coating will greatly expand its real-world application fields.

Effect of Ni-5Al Addition on the Properties of BaAl2O4-Based Coating Deposited with a Novel Explosive Spray Coating Technique

Effect of Ni-5Al Addition on the Properties of BaAl2O4-Based Coating Deposited with a Novel Explosive Spray Coating Technique

A biodegradable and antimicrobial polymer coating for metal implants for the prevention of prosthetic joint infection

The aim of this project is to produce antibiotic-loaded poly (lactic-co-glycolic acid) (PLGA) polymer films by airbrush onto orthopaedic implants to address prosthetic joint infections (PJIs). It covered the development of an airbrush spray-coating technique, the selection and assessment of polymers and antibiotics, sample characterisation and antibacterial studies. The initial results are encouraging as the PLGA coatings exhibited a sustained drug release pattern and antibacterial ability against causative pathogens. Moreover, these PLGA coatings also possessed rapid degradation within 4 weeks which could provide favourable conditions for osseointegration. Furthermore, cytotoxicity assessment of final coatings will need to be conducted to ensure biocompatibility, as well as to determine the effect of each coating on osseointegration. Finally, the development of alternative coating techniques which are more cost-effective and suitable for large-scale production might be the direction of future research. 

Effect of Protonation Doping of Polyaniline Electrodes using Hydrochloric Acid on Its Pseudocapacitor Capacitance

Pseudocapacitor is a supercapacitor that can store charge faradically through a reversible redox reaction. Polyaniline (PANi) is one of the promising active materials for pseudocapacitor electrodes since it can produce theoretical specific capacitance up to 750 F/g. We prepared leucomeraldine base polyaniline (LB-PANi) electrodes by deposition of dissolved LB-PANi powder in N,N-Dimethylformamide (DMF) using spraycoating technique. The LB-PANi electrodes was then doped with 1 M HCl through protonation process to obtain emeraldine salt polyaniline (ES-PANi) electrodes. We used both electrode materials and 1 M KCl to prepare a symmetrical sandwich supercapacitor model of <LB-PANi|KCl|LB-PANi> and <ES-PANi|KCl|ES-PANi>, as well as measured their performance. The results show a significant increase of the specific capacitance of PANi supercapacitor from 15.02 F/kg to 1876.87 F/kg when the electrodes of the LB-PANi were changed with the ES-PANi electrodes.

Reinforced Nafion Membrane with Ultrathin MWCNTs/Ceria Layers for Durable Proton-Exchange Membrane Fuel Cells.

For further commercializing proton-exchange membrane fuel cells, it is crucial to attain long-term durability while achieving high performance. In this study, a strategy for modifying commercial Nafion membranes by introducing ultrathin multiwalled carbon nanotubes (MWCNTs)/CeO2 layers on both sides of the membrane was developed to construct a mechanically and chemically reinforced membrane electrode assembly. The dispersion properties of the MWCNTs were greatly improved through chemical modification with acid treatment, and the mixed solution of MWCNTs/CeO2 was uniformly prepared through a high-energy ball-milling process. By employing a spray-coating technique, the ultrathin MWCNTs/CeO2 layers were introduced onto the membrane surfaces without any agglomeration problem because the solvent rapidly evaporated during the layer-by-layer stacking process. These ultrathin and highly dispersed MWCNTs/CeO2 layers effectively reinforced the mechanical properties and chemical durability of the membrane while minimizing the performance drop despite their non-ion-conducting properties. The characteristics of the MWCNTs/CeO2 layers and the reinforced Nafion membrane were investigated using various in situ and ex situ measurement techniques; in addition, electrochemical measurements for fuel cells were conducted.

Spray-Coated Superhydrophobic Overlayer with Photothermal and Electrothermal Functionalities for All-Weather De/anti-icing Applications.

High-performance de/anti-icing overlayers which can be deposited on diverse surfaces offer great potential in many industrial settings and daily life, yet a versatile overlayer applicable to all-weather conditions (high humidity, low temperature, raining, snowing, etc.) is in high demand for practical applications. This study presents the fabrication and application of a superhydrophobic overlayer with a bioinspired hierarchical surface which additionally possesses photothermal and electrothermal functionalities, so it can operate as a de/anti-icing layer in extreme environments. The overlayer, with a papilla-like microstructure similar to that of a lotus leaf, features polydopamine-decorated layered basic zinc acetate microparticles distributed in the framework of multiwalled carbon nanotubes. Specifically, the overlayer is superhydrophobic, and its capability of suppressing the condensation of water droplets and growth of ice crystals is verified by both in situ environmental scanning electron microscopy observations and freezing experiments. Moreover, the overlayer can be warmed up to 74 and 105 °C under the excitation of sunlight and direct current bias, respectively, which is sufficiently high for deicing in severe weather. It is worth mentioning that the overlayer is produced by a spray-coating technique; therefore, it is suitable for large-scale deployment on arbitrary substrate materials. The findings provide insights into a new strategy for engineering multifunctional overlayers and can lead to expanding applications of composite coatings.

A hybridized nano-porous carbon reinforced 3D graphene-based epidermal patch for precise sweat glucose and lactate analysis

Wearable electrochemical biosensors for perspiration analysis offer a promising non-invasive biomarker monitoring method. Herein, a functionalized hybridized nanoporous carbon (H-NPC)-encapsulated flexible 3D porous graphene-based epidermal patch was firstly fabricated for monitoring sweat glucose, lactate, pH, and temperature using simple, cost-effective, laser-engraved, and spray-coating techniques. The fabricated H-NPC-modified electrode significantly increased electrochemical surface area and electrocatalytic activity. Within the physiological sweat range (0–1.5 mM), the second-generation glucose sensor exhibited an excellent sensitivity of 82.7 μAmM−1cm−2 with 0.025 μM LOD. Moreover, the lactate biosensor exhibited an extraordinary linear range (0–56 mM) response owing to the incorporation of an outer diffusion limiting layer (DLL) that controls the lactate flux reaching the enzyme with comparable sensitivity (204 nAmM−1cm−2) and LOD (4 μM). Finally, we employed an analytical correction approach incorporating pH and temperature adjustments during on-body tests. In addition to connecting various carbon-based materials to limitless metal-organic frameworks as a transduction material, our research also paves the way for enabling these sensors to operate on pH and T correction independently while delivering accurate results.

Durable self-cleaning nano-titanium dioxide superhydrophilic coating with anti-fog property

PurposeThis paper aims to design the nano-titanium dioxide (TiO2) coating system which has superhydrophilic property, self-cleaning mechanism and antifog property as well as strong adhesion on glass substrate.Design/methodology/approachTwo hydrophilic materials have been used such as TiO2 nanoparticles as fillers and hydrophilic copolymer, Pluronic F-127 by using simple sol–gel approach. The prepared solution was applied onto glass through dip- and spray-coating techniques and then left for drying at ambient temperature.FindingsThe nano-TiO2 superhydrophilic coating has achieved the water contact angle of 4.9° ± 0.5°. The superhydrophilic coating showed great self-cleaning effect against concentrated syrup and methylene blue where thin layer of water washes the dirt contaminants away. The nano-TiO2 coating exhibits great antifog performance that maintains high transparency of around 89% when the coated glass is placed above hot-fog vapor for 10 min. The fog droplets were condensed into water film which allowed the transmission of light through the glass. The strong adhesion of coated glass shows no total failure at scratch profile when impacted with scratch load of 500, 800 and 1,200 mN.Research limitations/implicationsFindings will be useful in the development of self-cleaning superhydrophilic coating that is applicable on building glass and photovoltaic panel.Practical implicationsThe developed nano-TiO2 coating is developed by the combination of hydrophilic organic copolymer–inorganic TiO2 network to achieve great superhydrophilic property, optimum self-cleaning ability and supreme antifog performance.Social implicationsThe findings will be useful for residents in building glass window where the application will reduce dust accumulation and keep the glass clean for longer period.Originality/valueThe synthesis of nano-TiO2 superhydrophilic coating which can be sprayed on large glass panel and cured at ambient temperature.

Strain self-sensing capability of a tidal turbine blade fabricated of PU-foam/glass fiber/epoxy composites using MWCNTs

A novel marine composite structure (experimental tidal turbine blade) made up of a polyurethane (PU) foam/glass fiber/epoxy resin composite with multiwall carbon nanotubes (MWCNTs) is proposed herein to self-sense its strain under a structural test scenario. To achieve this, MWCNTs were deposited onto glass fiber fabric by spray-coating technique in order to form an effective electrical percolation network onto the external skin surface of the tidal turbine blade which enables piezoresistive capability. After MWCNT deposition, the blade was manufactured by means of one-shot resin transfer molding (RTM) in a closed and heated metallic mold specially designed with a blade geometry of 67 cm length. The results confirm that the spray coating technique is a viable method to deposit MWCNTs onto glass fiber surface and form electrical networks into the blade at a relatively low MWCNT concentration. Finite element analysis (FEA) predicted a suitable structural blade design with a maximum failure index value of 0.9 attained in the blade shear web. The measured longitudinal strains of the tidal turbine blade were in good agreement with the numerical strain values predicted with FEA. Electromechanical tests carried out on a structural test rig designed and instrumented for tidal turbine blades showed that the electrical resistance change response of carbon nanotube (CNT) network integrated into the blade was capable of following the mechanical curve response up to the blade limit load, confirming its ability to self-sense its strain in real time.

Surface Adsorption-Assisted Visible and Near-Infrared Photodetection in SrTiO3 Nanostructures

Perovskites are relatively less explored materials in the domain of visible and near-infrared (NIR) photodetection. This study represents high-performance visible and NIR photodetection by using SrTiO3 nanostructures. Two nanoforms of SrTiO3, that is, nanograss and hollow spheres, were synthesized by a cost-effective facial hydrothermal route. The SrTiO3 nanoforms were then characterized using various microscopic and spectroscopic techniques to ensure their morphology, structures, crystallinity, and chemical compositions. Thin films of SrTiO3 nanostructures were then deposited on a Au interdigitized electrode-based SiO2/Si substrate by the spray-coating technique to fabricate the photodetectors. Both the SrTiO3 nanostructures, that is, grass- and hollow sphere-based photodetectors, were characterized under visible (532 nm) and NIR (905) light radiation. The grass/hollow sphere showed a responsivity of 1.6/0.4736 mA/W and a detectivity of 13.62 × 109/10.83 × 109 Jones in visible light. Under NIR illumination, responsivity and detectivity were measured as 2.42/0.1936 mA/W and 21.58 × 109/5.32 × 109 Jones for grass/hollow sphere samples, respectively. Overall, the SrTiO3 grass nanostructure showed relatively better photoresponse both in the visible and NIR regions. Both the SrTiO3 nanostructures exhibited highly stable photodetection after a long period of time. The sensors were then tested in vacuum and compared with ambient air to confirm the strong influence of surface adsorption of the oxygen species in photoresponse.

Superhydrophobic starch-based cryogels modified with silylated magnetic nanoparticles for oil spill cleanup

Superhydrophobic smart adsorbents have attracted wide attention for the cleanup of oil spill that endangers the aquatic ecosystem. Herein, a super-water-repellent coating (HOS/Fe3O4) was achieved through hydrolytic condensation of hexadecyltrimethoxysilane and tetraethyl orthosilicate in the presence of Fe3O4 nanoparticles. The coating was then introduced onto the surface of starch cryogel (SC) by spray-coating technique to fabricate the superhydrophobic and magnetic starch-based adsorbent (HOS/Fe3O4@SC). The surface chemical composition and hierarchical micro/nanostructures that contribute to the high water contact angle (>151°) and low sliding angle (<5°) of the as-obtained material were characterized in detail. The HOS/Fe3O4@SC exhibited excellent water repellent, self-cleaning, and anti-fouling properties. The structural support and stable chemical bonding endow the material with good mechanical and chemical durability. The HOS/Fe3O4@SC also possessed reasonable adsorption capacities to various organic solvents, and its oil absorption kinetics was also comprehensively studied. The HOS/Fe3O4@SC can be applied for heavy oil absorption underwater and magnetically guided oil slick cleaning. This novel starch-based absorbent exhibits promising application in tackling oil contamination in complex environments.

Effect of Solvent on Superhydrophobicity Behavior of Tiles Coated with Epoxy/PDMS/SS.

Superhydrophobic coatings are widely applied in various applications due to their water-repelling characteristics. However, producing a durable superhydrophobic coating with less harmful low surface materials and solvents remains a challenge. Therefore, the aim of this work is to study the effects of three different solvents in preparing a durable and less toxic superhydrophobic coating containing polydimethylsiloxane (PDMS), silica solution (SS), and epoxy resin (DGEBA). A simple sol-gel method was used to prepare a superhydrophobic coating, and a spray-coating technique was employed to apply the superhydrophobic coating on tile substrates. The coated tile substrates were characterized for water contact angle (WCA) and tilting angle (TA) measurements, Field-Emission Scanning Electron Microscopy (FESEM), Atomic Force Microscopy (AFM), and Fourier Transform Infrared Spectroscopy (FTIR). Among 3 types of solvent (acetone, hexane, and isopropanol), a tile sample coated with isopropanol-added solution acquires the highest water contact angle of 152 ± 2° with a tilting angle of 7 ± 2° and a surface roughness of 21.80 nm after UV curing for 24 h. The peel off test showed very good adherence of the isopropanol-added solution coating on tiles. A mechanism for reactions that occur in the best optimized solvent is proposed.

Effect of impurities on the Raman spectra of spray-coated β-Ga2O3 thin films

Here, the incorporation of impurities into doped thin β-Ga2O3 films was studied by Raman spectroscopy, and a simple spring model was employed to estimate the impurity concentration from the impurity-modified frequencies of first-order phonon modes. β-Ga2O3 thin film samples were prepared using the spray-coating technique. As impurities, we used rare earth atoms (Er, Sm, and Gd) as well as Mg, Al, and Zn, with the nominal impurity concentrations varying from 0.5% up to 5.0%. As the impurities are expected to predominantly occupy Ga sites in the β-Ga2O3 lattice, heavier and lighter atoms than Ga should have a pronounced influence on Ga-related lattice vibrations. Therefore, in the Raman spectra of the thin films measured using 325-nm excitation, the impurity-induced shifts of the frequencies of vibrations involving Ga and O atoms were employed to estimate the impurity concentration. In addition, a high-impurity concentration can cause the formation of impurity-related oxides, as it is clearly visible for Zn. Besides, the Raman spectra with Mg as the impurity show that Mg most probably occupies interstitial rather than substitutional sites as the Raman modes do not shift with respect to the impurity concentration.

Exploring the Capabilities of a Piezoresistive Graphene-Loaded Waterborne Paint for Discrete Strain and Spatial Sensing.

The development of a piezoresistive coating produced from dispersing graphene nanoplatelets (GNPs) inside a commercial water-based polyurethane paint is presented. The feasibility of its exploitation for realizing highly sensitive discrete strain sensors and to measure spatial strain distribution using linear and two-dimensional depositions was investigated. Firstly, the production process was optimized to achieve the best electromechanical response. The obtained materials were then subjected to different characterizations for structural and functional investigations. Morphological analyses showed a homogenous dispersion of GNPs within the host matrix and an average thickness of about 75 µm of the obtained nanostructured films. By several adhesion tests, it was demonstrated that the presence of the nanostructures inside the paint film lowered the adhesion strength by only 20% in respect to neat paint. Through electrical tests, the percolation curve of the nanomaterial was acquired, showing an effective electrical conductivity ranging from about 10−4 S/m to 3.5 S/m in relation to the different amounts of filler dispersed in the neat paint: in particular, samples with weight fractions of 2, 2.5, 3, 3.5, 4, 5 and 6 wt% of GNPs were produced and characterized. Next, the sensitivity to flexural strain of small piezoresistive sensors deposited by a spray-coating technique on a fiberglass-reinforced epoxy laminate beam was measured: a high gauge factor of 33 was obtained at a maximum strain of 1%. Thus, the sensitivity curve of the piezoresistive material was successively adopted to predict the strain along a multicontact painted strip on the same beam. Finally, for a painted laminate plate subjected to a mechanical flexural load, we demonstrated, through an electrical resistance tomography technique, the feasibility to map the electrical conductivity variations, which are strictly related to the induced strain/stress field. As a further example, we also showed the possibility of using the coating to detect the presence of conducting objects and damage.

3D spray-coated gradient profile ceramic membranes enables improved filtration performance in aerobic submerged membrane bioreactor

Rational design of cross-sectional microstructure in ceramic membranes has shown to improve membrane filtration efficacy without affecting rejection performance. In this work, we adopted 3D spray-coating technique to generate multi-layered membrane layers on macro-porous flat-sheet ceramic supports. The thickness of each layer was controlled by spray-coating cycles, and a gradient membrane layer was rationalized by successively coating three ceramic slurries containing alumina powders of gradually refined particle sizes, followed by co-sintering. Gradient membrane layers on both sides of the various sized flat-sheet ceramic supports were fabricated. Compared to the non-gradient counterpart, the gradient membranes showed both higher pure water flux (at the same TMP) and lower membrane resistance, which clearly evidenced the benefits of gradient profile in the membrane layer. Further, their performance in aerobic membrane bioreactors (AeMBR) was comparably studied for the first time. The treatment performance was not significantly affected by the types of membranes used, while the gradient membrane showed better filtration performance (i.e., a slower rise in TMP). Although the fouling mechanisms were revealed to be similar, the fouling layer in the gradient membrane was composed of a higher percentage of smaller foulants compared to that of the non-gradient counterpart. The observed differences were closely correlated to the larger internal pore structure in the gradient membrane. The present work provides a feasible 3D spray-coating technique for the fabrication of gradient flat-sheet ceramic membranes, and clarifies the benefits in AeMBR for domestic wastewater treatment.