Spray-coating Technique Research Articles

High volumetric-energy-density flexible supercapacitors based on PEDOT:PSS incorporated with carbon quantum dots hybrid electrodes

Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is a highly successful conductive polymer utilized as an electrode material in energy storage units for portable and wearable electronic devices. Nevertheless, employing PEDOT:PSS in supercapacitors (SC) in its pristine state presents challenges due to its suboptimal electrochemical performance and operational instability. To surmount these limitations, PEDOT:PSS has been integrated with carbon-based materials to form flexible electrodes, which exhibit physical and chemical stability during SC operation. We developed a streamlined fabrication process for high-performance SC electrodes composed of PEDOT:PSS and carbon quantum dots (CQDs). The CQDs were synthesized under microwave irradiation, yielding green- and red-light emissions. Through optimizing the ratios of CQDs to PEDOT:PSS, the SC electrodes were prepared using a spray-coating technique, marking a significant improvement in device performance with a high volumetric capacitance (104.10 F cm−3), impressive energy density (19.68 Wh cm−3), and excellent cyclic stability, retaining ∼85% of its original volumetric capacitance after 15,000 repeated GCD cycles. Moreover, the SCs, when utilized as a flexible substrate, demonstrated the ability to maintain up to ∼85% of their electrochemical performance even after 3,000 bending cycles (at a bending angle of 60°). These attributes render this hybrid composite an ideal candidate for a lightweight smart energy storage component in portable and wearable electronic technologies.

Achieving Antibiofouling on Microporous Membranes Prepared with a Green Solvent via Spraying an Aqueous Antifouling Copolymer Solution

This study highlights a comprehensive investigation into the fabrication and characterization of sustainable membranes for antifouling applications. It utilizes γ-valerolactone as a green solvent to obtain microfiltration PVDF membranes, and leverages spray-coating technique to modify these membranes. This research aims to enhance the surface and bulk properties of PVDF membranes while promoting sustainable practices. Chemical analyses of the membranes reveal that the surface and bulk of the membranes were successfully modified. Dynamic water contact angle measurements indicated that a 10 mg/mL coating solution (PVDF_10) resulted in the highest hydrophilicity. Different biofouling tests were conducted using proteins and bacteria. In adhesion tests with BSA, and E. coli, the PVDF_10 membrane demonstrated the highest resistance, reducing adhesion by approximately 83% and 94%, respectively. Additionally, cyclical water/bacterial filtration tests demonstrated that PVDF_10 membrane achieved a higher flux recovery ratio compared to commercial hydrophilic PVDF membranes. The modifications remained stable even after 6 weeks of immersion in water. This study highlights the potential of γ-GVL and the spray-coating technique as environmentally friendly solvents and modification techniques for producing green antifouling PVDF membranes, aligning with sustainable practices and significantly enhancing membrane performance.

Easily Applicable Superhydrophobic Composite Coating with Improved Corrosion Resistance and Delayed Icing Properties

Mitigating the adverse effects of corrosion failure and low-temperature icing on aluminum (Al) alloy materials poses significant research challenges. The facile fabrication of bioinspired superhydrophobic materials offers a promising solution to the issues of corrosion and icing. In this study, we utilized laboratory-collected candle soot (CS), hydrophobic fumed SiO2, and epoxy resin (EP) to create a HF-SiO2@CS@EP superhydrophobic coating on Al alloy surfaces using a spray-coating technique. Various characterization techniques, including contact angle meter, high-speed camera, FE-SEM, EDS, FTIR, and XPS, were employed to investigate surface wettability, morphologies, and chemical compositions. Moreover, a 3.5 wt.% NaCl solution was used as a corrosive medium to evaluate the corrosion resistance of the uncoated and coated samples. The results show that the capacitive arc radius, charge transfer resistance, and low-frequency modulus of the coated Al alloy significantly increased, while the corrosion potential (Ecorr) shifted positively and the corrosion current (Icorr) decreased by two orders of magnitude, indicating improved corrosion resistance. Additionally, an investigation of ice formation on the coated Al alloy at −10 °C revealed that the freezing time was 4.75 times longer and the ice adhesion strength was one-fifth of the uncoated Al alloy substrate, demonstrating superior delayed icing and reduced ice adhesion strength performance.

Improving multifunctional properties of the polyvinylidene fluoride (PVDF) membrane with crosslinked dialdehyde-starch (DAS) and polyethyleneimine (PEI) coating

Dialdehyde-soluble starch (DAS) and polyethyleneimine (PEI) were used to coat the polyvinylidene fluoride (PVDF) membrane for improving its antifouling and multifunctional properties through a combination of dip-coating and spray-coating techniques. The resulting membrane demonstrated excellent hydrophilicity and underwater oleophobicity due to hydrophilic DAS and PEI on its surface. The membrane achieved an impressive oil removal rate of 99.8 % and a flux 1420.8 ± 26.5 L·m−2·h−1 when it was used for oil-water emulsion separation. The hydration layer formed by the DAS and PEI greatly enhanced the membrane antifouling property, and its flux recovery rate was up to 96.6 % in BSA filtration experiments. The positive charge PEI and the negative charge DAS contributed to high separation efficiency of 99.1 % for the anion dye MO with the membrane D10P20, and high separation efficiency of 88.3 % for the cation dye RhB with the membrane P5D20. In addition, the coating layer was stable due to the cross-linked DAS and PEI. This research contributes greatly to the preparation of antifouling and multifunctional membrane using environmentally friendly material including polysaccharide derivatives and water soluble polymer.

Spray-coated PDA-wrapped carboxylic CNT/PES membrane to augment fouling mitigation, organic removal, and membrane stability in electrochemical membrane filtration

This study introduces robust and conductive polydopamine (PDA)-wrapped carboxylic carbon nanotube (C-CNT)-coated polyethersulfone (PES) membrane for electrochemical membrane filtration to treat greywater. Self-polymerized dopamine was prepared directly under oxidative conditions on the CNT strands, followed by their immobilizations on the surface of the PES membrane through a novel spray-coating technique. The spraying coating technique improved both the durability of the coating layer and membrane permeability by 27 % higher than that prepared by the conventional vacuum filtration method. The spraying coating technique enhanced the electroactive properties of the PDA/C-CNT membrane so that the fouling rate was reduced more effectively than the C-CNT membrane or bare PES membrane. Fouling mitigation of the PDA/C-CNT membrane was attributed to the combined effect of electrostatic repulsions between the foulants and the conductive membrane surface along with degradation of organic compounds by electrochemical oxidation. The constant current density profile also confirmed the structural stability of the conductive layer on the membrane under both cathodic and anodic conditions. Furthermore, the fouling layer formed by membrane filtration was removed effectively by in-situ anodic cleaning. Over 80% of water permeability was recovered without losing the membrane integrity up to 3 consecutive anodic cleaning cycles.

Transparent Superhydrophobic and Self-Cleaning Coating.

Surface roughness and low surface energy are key elements for the artificial preparation of biomimetic superhydrophobic materials. However, the presence of micro-/nanostructures and the corresponding increase in roughness can increase light scattering, thereby reducing the surface transparency. Therefore, designing and constructing superhydrophobic surfaces that combine superhydrophobicity with high transparency has been a continuous research focus for researchers and engineers. In this study, a transparent superhydrophobic coating was constructed on glass substrates using hydrophobic fumed silica (HF-SiO2) and waterborne polyurethane (WPU) as raw materials, combined with a simple spray-coating technique, resulting in a water contact angle (WCA) of 158.7 ± 1.5° and a sliding angle (SA) of 6.2 ± 1.8°. Characterization tests including SEM, EDS, LSCM, FTIR, and XPS revealed the presence of micron-scale protrusions and a nano-scale porous network composite structure on the surface. The presence of HF-SiO2 not only provided a certain roughness but also effectively reduced surface energy. More importantly, the coating exhibited excellent water-repellent properties, extremely low interfacial adhesion, self-cleaning ability, and high transparency, with the light transmittance of the coated glass substrate reaching 96.1% of that of the bare glass substrate. The series of functional characteristics demonstrated by the transparent superhydrophobic HF-SiO2@WPU coating designed and constructed in this study will play an important role in various applications such as underwater observation windows, building glass facades, automotive glass, and goggles.

Bilayer coating fabricated on aluminum alloy substrates with superamphiphobicity, corrosion resistance, self-cleaning, and delayed icing properties

To address the functional failure caused by low-surface-tension liquid wetting and adhesion in superhydrophobic materials, in this study, we constructed a bilayer coating with superamphiphobic properties using an epoxy (Ep) bonding layer and an organosilane-grafted attapulgite (OG-ATP) layer through spray-coating technique. The prepared superamphiphobic bilayer coating exhibited high contact angles (CAs) and low sliding angles (SAs) for cold water (25 °C), hot water (85 °C), glycerol, ethylene glycol, peanut oil, and even n-hexadecane (CA = 150.4 ± 0.3° and SA = 7 ± 2°) with surface tension of 27.5 mN m−1. Surface morphology and elemental analysis confirmed the coating's unique micro-nano hierarchical structure and low surface energy characteristics. Electrochemical impedance spectroscopy (EIS) results showed that the surface charge transfer resistance (Rct) and low-frequency modulus (|Z|0.01Hz) were enhanced by 6–7 orders of magnitude compared to the bare aluminum alloy substrate. The anti-corrosion performance remained stable even after 5 days of 3.5 wt% NaCl immersion. Additionally, icing experiments with water droplets at −10 °C and −15 °C revealed a significant delay in ice formation on the substrate protected by the bilayer coating. The development of this protective material, combining superamphiphobicity, self-cleaning, corrosion resistance, and anti-icing functions, will provide advanced technological reserves in areas such as marine, aviation, transportation, and manufacturing.

Low-temperature preparation of nanostructured porous sol-gel anti-reflective coating for near-infrared wavelengths

Anti-reflective coatings are crucial in minimizing reflection between different optical media at the interfaces. This study aims to develop an anti-reflective layer for the near-infrared region using a sol-gel coating method combined with a low-temperature plasma-jet-assisted surfactant extraction. For the deposition of the sol-gel layer on glass and polycarbonate substrates, dip-coating and spray-coating techniques were used. Surfactant removal was carried out using a plasma-jet and solvent exchange. Some of the samples were also annealed at 450 °C. The samples were characterized through light transmission measurements, haze percentage determination, 3D laser scanning microscopy, scanning electron microscopy, profilometry, Fourier transform Infrared spectroscopy, ellipsometry and atomic force microscopy. The results showed that the anti-reflective coating layer treated with a plasma-jet and solvent exchange at room temperature demonstrated broadband anti-reflective properties with high transmission in near-infrared regions (up to 7.6% relative improvements in transmission for two sides). Annealing, performed only on the glass substrate, also showed the maximum relative improvement in transmission up to 8% for two sides. Moreover, in the case of polymer-based substrates, a low-temperature process is essential, which is implemented successfully by a plasma-jet method. These findings highlight the effectiveness of the proposed method for fabricating anti-reflective layers on both glass and polycarbonate substrates, offering potential applications in various industries, e.g. where either low-temperature fabrication or cost-cutting, quick and “simple” production methods play a major role for the feasibility of products as in mass markets.

Ceramic nanoparticle based flexible hydrovoltaic devices for tactile and respiratory signal detection

Devices that utilize water evaporation or moisture to generate electricity have received significant research attention in the field of energy conversion and harvesting. Herein, a device capable of generating electricity through the process of water evaporation has been created, utilizing medical nonwoven fabric as a porous substrate with simple dip-coating and spray-coating techniques. The device constructs a multitude of nanopores on the substrate by employing a blend of Al2O3 nanoparticles of varying dimensions. The electrical output of the device was stable at 0.55 V and 6 μA from a small water supply, as confirmed by the test. The device can easily recognize the click of a finger through the release of minuscule amounts of water during the contact. Furthermore, the device has the ability to recognize various breathing patterns, such as normal breathing, rapid breathing, and wheezing that may induced by diseases. This work developed a flexible device for power generation by water evaporation process and provides a referable idea for human related humidity sensing.

High corrosion resistance of a novel armored super-hydrophobic Fe-Mn-Si-Cr-Ni coating

In this work, ultrasonic-assisted laser cladding technology was employed to fabricate shape memory alloy (SMA) coatings composed of Fe-Mn-Si-Cr-Ni on the surface of 304 stainless steel. Both experimental and simulated results unequivocally demonstrate a substantial improvement in both microhardness and wear resistance of the metal surface. Subsequently, a superhydrophobic coating with an “armor-like” structure was comprehensively prepared by integrating femtosecond laser (FSL) and nano SiO2 spray-coating techniques. The creation of this microstructure on the coating surface efficiently facilitated the high-efficiency embedding of nano SiO2 particles. Notably, the modified SMA coating exhibited stable superhydrophobic properties and exceptional corrosion resistance. This research not only provides novel approaches and methods for the preparation and modification of Fe-based memory alloy coatings but also highlights potential applications in the corrosion-resistant field. The work offers valuable insights for researchers in the field of materials science, emphasizing the synergistic effects of ultrasound-assisted laser cladding technology, femtosecond laser, and nano SiO2 spraying techniques. It provides robust support for the development of new functional coatings.

Assessing Detoxification Performance of Metal Hydroxide@Polymer Composites Prepared via Matrix-Incorporation and Spray-Coating Techniques

Assessing Detoxification Performance of Metal Hydroxide@Polymer Composites Prepared via Matrix-Incorporation and Spray-Coating Techniques

LiFePO4-coated carbon fibers as positive electrodes in structural batteries: Insights from spray coating technique

This study presents the fabrication of LiFePO4 (LFP)-coated carbon fibers (CFs) as a positive electrode component for structural batteries, utilizing a spray coating technique. The successful coating of CFs through this method demonstrated their usefulness as efficient current collectors. The electrodes obtained using this method underwent electrochemical evaluations. Throughout the extended cycling tests at C/7, the maximum specific discharge capacity reached 146 mAh/g, maintaining a 77% capacity retention after 100 cycles. In rate performance assessments at the faster C-rate of 1.5C, the capacity measured 123 mAh/g, with a retention of 96%. The application of spray coating emerges as a promising technique for electrode production in structural batteries, showcasing its potential for optimizing performance in multifunctional energy storage systems.

Innovative mushroom-like hemp-based evaporators enhanced by biochar for efficient seawater desalination

Inadequate access to clean water and wasteful resource consumption during production pose significant challenges in global development. To combat these issues, interfacial solar steam generation (ISSG) has emerged as an energy-efficient solution to mitigate the ongoing water scarcity crisis. However, the application of ISSG is hindered by high costs and intricate fabrication processes associated with synthetic functional materials. In response, this study introduces an innovative approach that repurposes abundant by-products generated from hemp fiber production. Hemp fiber noil are transformed into a nonwoven fabric substrate, onto which hemp stem-derived biochar is seamlessly integrated using a straightforward spray-coating technique, establishing an efficient solar-to-heat conversion evaporator. Leveraging the durability of hemp fibers, this system achieves an impressive seawater evaporation rate of 1.47 kg m−2 h−1 under 1 sun condition, making it highly competitive in seawater desalination research. This pioneering strategy combines waste green materials and their functional counterparts, unlocking practical applications, addressing resource scarcity, and mitigating environmental pollution. This research highlights the potential of sustainable material utilization to tackle pressing global challenges.

Fast-Crosslinking Enabled Self-Roughed Polydimethylsiloxane Transparent Superhydrophobic Coating and Its Application in Anti-Liquid-Interference Electrothermal Device.

Polydimethylsiloxane (PDMS)-based transparent and superhydrophobic coatings have important applications, such as anti-icing, corrosion resistance, self-cleaning, etc. However, their applications are limited by the inevitable introduction of nanoparticles/high-temperature/segmented PDMS to facilitate a raspy surface. In this study, a self-roughed, neat PDMS superhydrophobic coating with high transparency is developed via a one-step spray-coating technique. PDMS suspensions with various droplet sizes are synthesized and used as building blocks for raspy surface formation by controlled curing on the warm substrate. The optimal coating exhibits a large water contact angle of 155.4° and transparency (T550 = 82.3%). Meanwhile, the employed spray-coating technique is applicable to modify a plethora of substrates. For proof-of-concept demonstrations, the use of the PDMS hydrophobic coating for anti-liquid-interference electrothermal devices and further transparent observation window for long-term operation in a sub-zero environment is shown successful. The proposed facile synthesis method of hydrophobic PDMS coating is expected to have great potential for a broad range of applications in the large-scale fabrication of fluorine-free, eco-friendly superhydrophobic surfaces.

Hybrid superamphiphobic anti-corrosion coating with integrated functionalities of liquid repellency, self-cleaning, and anti-icing

Superhydrophobic materials have shown tremendous potential in various fields. However, the adhesion, wetting, and pinning of low-surface-tension liquids greatly limit their multifunctional applications. Therefore, the creation of superamphiphobic coatings that combine superhydrophobic and superoleophobic properties through a simple preparation strategy is desirable. In this study, we successfully developed an organic-inorganic hybrid superamphiphobic coating on Q235 carbon steel using aluminum oxide nanoparticles, organosilanes, and waterborne epoxy resin via a versatile spray-coating technique. The coating exhibited high contact angles (> 151°) and low sliding angles (< 7°) for water and oil liquids, demonstrating excellent superamphiphobic characteristics. Electrochemical tests demonstrated significant improvements in charge transfer resistance and low-frequency modulus for the superamphiphobic coating. The corrosion potential shifted positively by 590 mV, and the corrosion current density decreased by four orders of magnitude. Additionally, the coating endured 480 h of salt spray and 2400 h of outdoor atmospheric exposure, showcasing superior anti-corrosion capacity. Freezing tests of water droplets at –10 °C and –15 °C confirmed that the coating significantly prolonged the freezing time with reduced ice adhesion strength. We believe that the designed superamphiphobic coating with integrated functionalities of self-cleaning, anti-corrosion, anti-icing, and anti-liquid-adhesion can provide important solutions for extending the lifespan of materials in marine and industrial environments.

Ca-Doped Copper (I) Oxide Deposited via the Spray Coating Technique for Heterojunction Solar Cell Application

In this report, the morphological, optical, electrical, and photovoltaic properties of copper oxide and calcium-doped copper oxide thin films produced via the spray coating method were studied. The thermal post treatment at 300 °C in an inert atmosphere allowed us to obtain a single phase of Cu2O with 21 Ωcm of resistivity (ρ). In this study, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, and 10 wt% Ca admixtures with copper oxide were investigated. The determined optimal calcium dopant concentration was 4 wt%. XRD analysis was used to reveal the chemical composition of the produced layers. It was found that a calcium dopant does not change the layer composition but improves its electrical parameters. Based on UV-Vis spectra, the band gap energy and Urbach energy were calculated. The morphology of produced thin films was described as smooth and nanocrystalline, corresponding to a grain size calculated based on the Scherrer equation. Finally, it was shown that the developed protocol of low-resistivity copper oxide deposition via the spray coating technique can be successfully implemented in heterojunction solar cell production. The I–V parameters of Ag/n-type CzSi/REF:CuOx and 4Ca:CuOx/Carbon were collected, and the achieved efficiency was 2.38%.

Biodegradable Conductive Layers Based on a Biopolymer Polyhydroxybutyrate/Polyhydroxyvalerate and Graphene Nanoplatelets Deposited by Spray-Coating Technique

In light of the growing concern for environmental protection and the alarming amount of waste produced due to hygiene regulations, this study suggests a biodegradable and eco-friendly solution that could make a significant contribution to the preservation of our planet. The developed solution was based on a polyhydroxybutyrate/polyhydroxyvalerate biopolymer, which has been tested regarding its physicochemical parameters and possible use in printed electrically conductive structures. Graphene nanoplatelets have been used as the conductive functional phase, due to literature reports of their potential use in biomedical applications and due to the potential of providing cytocompatibility in electrical structures by carbon nanomaterials. Prepared composites have been spray-coated onto PET film and paper substrates and then subjected to electrical, adhesion and optical measurements. In order to establish the conductivity of the developed composite, its resistance, layer thickness and surface topography were measured. Optical parameters have been specified using scanning electron microscopy (SEM) imaging and spectrophotometry. The conducted research opens a wide path for the use of the polyhydroxybutyrate/polyhydroxyvalerate biopolymer with graphene nanoplatelets in biomedical applications, ensuring good conductivity, biocompatibility and stability.

Natural convection in vertical solar heat collector nanotextured with reduced graphene oxide and silver nanowires

In this study, a vertical shaft is coated using silver nanowires (AgNWs) together with reduced graphene oxide (rGO) via the supersonic spray-coating technique to enhance the absorption of solar radiative heat for use in solar air heaters. The rGO/AgNW-coated surface induces multiple light reflections, similar to that in a perfect black body inside a Helmholtz jar, thus enhancing the collection of solar radiation. Air fed into the vertical heated shaft ascends owing to buoyancy. The air temperature difference, ΔT, between the outlet and inlet is measured for various mass flow rates to quantify the heat transferred to the air from the solar-heated vertical shaft. The longitudinal air velocity and temperature distributions inside the shaft are numerically simulated using the fire dynamics simulator. Both two- and three-dimensional simulations are performed, and the results are compared with experimental data for various mass flow rates. The results confirm that the trends observed in both the experiments and simulations agree well for all cases. Multiple metal meshes are installed inside the vertical shaft to induce turbulence, which enhances the heat transfer intensity. This turbulence enhancement is confirmed via smoke visualization and infrared images.

Porous Thin Films with Large Specific Surface Area on the Basis of Spray-Coated Metal Aerogels

The preparation of aerogels in the form of thin films deposited on a substrate (e.g., as an electrode material) is an attractive but challenging task. Such thin films are expected to combine the highly porous gel nanostructure, good mechanical stability, and a remarkably high specific surface area with efficient charge-carrier transport via the interconnected nanoparticle chains. All together, they make them attractive for the fabrication of (electro)catalysts or sensors for microfluidics, flexible electrodes for microelectronics, soft electrodes compatible with a stress-sensitive bioenvironment, etc. In this work, thin aerogel films of colloidal Pd and PtNi building blocks were prepared from the corresponding wet gels using a spray technique. The films were fabricated on substrates of around 1.5 cm2. During the modification of the substrates, the film thickness can be adjusted by controlling the ink content (flow rate, gas pressure, and temperature) and the number of spray cycles. In this way, both the electrical (down to Rs = ∼0.2 kOhm/sq) and optical parameters of the thin porous films can be tuned. Comparative studies of the pore and surface structures of the films have confirmed their integrity and the highly porous structure typical for aerogels. In perspective, spray-coated aerogels can be easily adapted to industrial applications because upscaling is possible and expensive equipment such as supercritical or freeze-dryers is not required. It is important to note that the spray-coating technique is applicable through a mask or can be converted to inkjet printing, which allows for the desired micropatterning of aerogel thin films.

Green fabrication of durable foam composites with asymmetric wettability by an emulsion spray-coating method for photothermally induced crude oil cleanup

Chemical spills, especially oil spills, are becoming an increasingly serious environmental issue. It remains a challenge to develop green techniques to prepare mechanically robust oil–water separation materials, especially those capable of separating high-viscosity crude oils. Herein, we propose an environmentally friendly emulsion spray-coating method to fabricate durable foam composites with asymmetric wettability for oil–water separation. After the emulsion, composed of acidified carbon nanotubes (ACNTs), polydimethylsiloxane (PDMS) and its curing agent, is sprayed onto melamine foam (MF), water in the emulsion is first evaporated, while PDMS and ACNTs are finally deposited on the foam skeleton. The foam composite exhibits gradient wettability and turns from superhydrophobicity of the top surface (the water contact angle reaches as high as 155.2°) to hydrophilicity of the interior region. The foam composite can be used for the separation of oils with different densities and has a 97% separation efficiency for chloroform. In particular, the photothermal conversion-induced temperature rise can reduce the oil viscosity and complete the high-efficiency cleanup of crude oil. This emulsion spray-coating technique and asymmetric wettability show promise for the green and low-cost fabrication of high-performance oil/water separation materials.