Search Results (69)

Electroless nickel deposition (ELD) is an autocatalytic technique extensively used to impart conductive, protective, and mechanical functionalities to inherently non-conductive synthetic substrates. This review systematically explores the fundamental mechanisms of electroless nickel deposition, emphasising recent advancements in surface activation methods, solvent systems, and microstructural control. Critical analysis reveals that bio-inspired activation methods, such as polydopamine (PDA) and tannic acid (TA), significantly enhance coating adhesion and durability compared to traditional chemical etching and plasma treatments. Additionally, solvent engineering, particularly using polar aprotic solvents like dimethyl sulfoxide (DMSO) and ethanol-based systems, emerges as a key strategy for achieving uniform, dense, and flexible coatings, overcoming limitations associated with traditional aqueous baths. The review also highlights that microstructural tailoring, specifically the development of amorphous-nanocrystalline hybrid nickel coatings, effectively balances mechanical robustness (hardness exceeding 800 HV), flexibility, and corrosion resistance, making these coatings particularly suitable for wearable electronic textiles and smart materials. Furthermore, commercial examples demonstrate the real-world applicability and market readiness of nickel-coated synthetic fibres. Despite significant progress, persistent challenges remain, including reliable long-term adhesion, internal stress management, and environmental sustainability. Future research should prioritise environmentally benign plating baths, standardised surface activation protocols, and scalable deposition processes to fully realise the industrial potential of electroless nickel coatings. Full article

Thiol–epoxy photopolymerization offers exceptional advantages for high-performance protective coatings, yet efficiently curing thick formulations remains a significant challenge due to the limited penetration depth of conventional UV light. Herein, we report a novel near-infrared (NIR) light-activated photopolymerization system for deep-curing applications, strategically integrating upconversion nanoparticles (UCNPs) as NIR-to-UV converters, isopropylthioxanthone (ITX) as a photosensitizer, and a liquid N-phenylglycine-based photobase generator (NPG-TBD) with enhanced resin solubility. Upon 980 nm NIR irradiation, photogenerated TBD efficiently catalyzes thiol–epoxy polymerization through an anionic mechanism, enabling uniform network formation with epoxy and thiol functional group conversions greater than 90% throughout samples exceeding 2.5 cm in thickness. The resulting coatings exhibit excellent mechanical properties including 3H pencil hardness, strong adhesion (0 grade), and good flexibility (2 mm), significantly outperforming conventional UV systems limited to approximately 1.5 mm. Additionally, the cured materials demonstrate multifunctional characteristics including distinctive upconversion luminescence and dual-responsive shape memory behavior. This approach addresses critical limitations in deep-photocuring technology while offering significant potential for applications in protective coatings for marine infrastructure, chemical storage facilities, and smart materials requiring both substantial barrier properties and programmable responsiveness. Full article

Hard, flexible, transparent, and hydrophobic multifunctional coatings have a wide range of applications, but they do not adequately protect against harsh conditions, especially photoaging. In this study, SiO₂ and Al₂O₃ nanoparticles were first modified by silazane and epoxy-functionalized silanes and then reacted with a polyetheramine curing agent to prepare highly crosslinked multifunctional hybrid coatings at room temperature. Due to the integration of siloxane nanoparticles and a polymer network, the multifunctional coatings presented outstanding hardness (4H), flexibility (bending diameter of 10 mm), and transmittance (>97%). The introduction of low-surface-energy PDMS and methyl-rich HMDS endowed the coatings with good hydrophobicity (water contact angle = 141.37°). The high reflectivity of SiO₂ and Al₂O₃ in the solar spectral region can help prevent photoaging of the coatings, improve their heat-shielding effect, and broaden their application scenarios. Compared with the traditional manufacturing methods, this study did not need ultraviolet irradiation, and the multifunctional transparent coatings could be prepared through a simple and efficient step-by-step strategy. Full article

Polyester-based polyurethane coatings were widely used in automotive, industrial, construction, and plastics industries due to their excellent mechanical properties, adhesion, and relatively outstanding oil and chemical resistance. In these coatings, the type and ratio of polyester and isocyanate curing agents influenced the cohesion energy, hydrogen bonding, crystallinity, crosslinking density, molecular weight, and morphology of the polyurethane at the microscopic level, thereby affecting the macroscopic mechanical properties, electrical performance, and environmental resistance of the material. However, there was limited systematic research on the effect of crosslinking density on the properties of polyester-based polyurethanes. In this study, an HTP-1 system was composed of neopentyl glycol (NPG) and phthalic anhydride (PA), and an HTP-2 system was composed of neopentyl glycol (NPG), hexahydrophthalic anhydride (HHPA), and adipic acid (AA). A series of polyesters (HTPs) were synthesized by adding polyols with different functional groups and adjusting their proportions in the system. The synthesized polyester was characterized using FT-IR, GPC, and DSC, and then cured with polyisocyanate curing agent N3390 to prepare the coating. The following properties of the films were evaluated: adhesion, impact resistance, pencil hardness, gloss, flexibility, oil resistance, and weather resistance. The results showed that in the HTP-1 system, the introduction of dipentaerythritol resulted in a polyester with a broad molecular weight distribution at high hydroxyl values, with a maximum PDI of 12.66 and a glass transition temperature (Tg) reaching 40.19 °C. The polyesters prepared by introducing three types of multifunctional polyols into the HTP-1 system exhibited good impact resistance, adhesion, and hardness. At low hydroxyl values, the coatings demonstrated good flexibility, but due to the lower crosslinking density, the oil resistance was poor. As the hydroxyl value increased, flexibility decreased, while oil resistance improved. In the HTP-2 system, coatings prepared with three different multifunctional polyols showed good impact resistance, flexibility, and hardness at low hydroxyl values but poor adhesion and oil resistance. As the hydroxyl value increased, adhesion improved from grade 1 to grade 0, and oil resistance improved for coatings prepared with trimethylolpropane and ditrimethylolpropane. However, the oil resistance of coatings prepared with dipentaerythritol decreased. Regarding weather resistance, the HTP-1-series resins primarily exhibited the cleavage of -CH₂ groups, while the HTP-2-series resins showed the cleavage of C-N bonds. Overall, the HTP-2 series resins demonstrated better weather resistance. In the high-hydroxyl-value HTP-2 system, the incorporation of trimethylolpropane or ditrimethylolpropane has been shown to produce coatings that achieve a balance among mechanical properties, flexibility, and oil resistance. This finding provides valuable insights for the design and development of high-performance polyester-based polyurethane coatings. Full article

Urushiol is recognized as a sustainable coating material with superior properties; however, it faces significant challenges in applications such as petrochemicals and marine engineering due to surface oil contamination. This study aimed to enhance the cleanability of urushiol-based coatings through hydrophilic modification. Polyethylene glycol monooleate (PEGMO) was identified as an appropriate hydrophilic macromonomer and utilized as a modifier to develop a novel urushiol-based coating, termed P(U-PEGMO), via thermal curing. The results indicated that copolymerization occurred between urushiol and PEGMO during the curing process, forming a stable urushiol copolymer with favorable compatibility. The incorporation of PEGMO greatly improved the surface hydrophilicity of the coatings, as evidenced by a reduction in the water contact angle to below 30° when the modifier content reached 30% or higher, demonstrating a high degree of surface hydrophilicity. This enhanced property imparted the modified coating with underwater superoleophobicity and reduced oil adhesion, thereby facilitating the removal of oil. The cleaning performance was evaluated using a simple water rinsing method, after which, less than 2.5 wt% of oil residues remained on the surface of the modified coating. The high hydrophilicity is considered responsible for the coating’s easy-cleaning capability. In addition, the modified coatings exhibited improved flexibility and impact resistance, albeit with a slight decrease in hardness. Full article

Artificial antireflective nanostructured surfaces, inspired by moth eyes, effectively reduce optical losses at interfaces, offering significant advantages in enhancing optical performance in various optoelectronic applications, including solar cells, light-emitting diodes, and cameras. However, their limited flexibility and low surface hardness constrain their broader use. In this study, we introduce a universal antireflective film by integrating nanostructures on both sides of a thin polycarbonate film. One side was thinly coated with Al₂O₃ for its high hardness, enhancing surface durability while maintaining flexibility. The opposite side was coated with SiO₂ to optimize antireflective properties, making the film suitable for diverse environments (i.e., air, water, and adhesives). This dual-coating strategy resulted in a mechanically robust and flexible antireflective film with superior optical properties in various conditions. We demonstrated the universal capabilities of our antireflective film via optical simulations and experiments with the fabricated film in different environments. Full article

Vibration sensors are widely applied in the detection of faults and analysis of operational states in engineering machinery and equipment. However, commercial vibration sensors with a feature of high hardness hinder their usage in some practical applications where the measured objects have irregular surfaces that are difficult to install. Moreover, as the operating environments of machinery become increasingly complex, there is a growing demand for sensors capable of working in wet and humid conditions. Here, we present a flexible, superhydrophobic vibration sensor with parallel microcracks. The sensor is fabricated using a femtosecond laser direct writing ablation strategy to create the parallel cracks on a PDMS film, followed by spray-coating with a conductive ink composed of MWCNTs, CB, and PDMS. The results demonstrate that the developed flexible sensor exhibits a high-frequency response of up to 2000 Hz, a high acceleration response of up to 100 m/s², a water contact angle as high as 159.61°, and a linearity of 0.9812 between the voltage signal and acceleration. The results indicate that the sensor can be employed for underwater vibration, sound recognition, and vibration monitoring in fields such as shield cutters, holding significant potential for mechanical equipment vibration monitoring and speech-based human–machine interaction. Full article

As the information age progresses, the electronics industry is evolving towards smaller and more sophisticated products. However, electrostatic potentials easily penetrate these components, causing damage. This underscores the urgent need for materials with superior antistatic properties to safeguard electronic devices from such damage. Antistatic coatings typically rely on polymers as the primary material, enhanced with conductive fillers and additives to improve performance. Despite significant progress, these coatings still face challenges related to advanced processing technologies and the integration of electrical and mechanical properties. Among various conductive fillers, the conducting polymer PEDOT:PSS stands out for its exceptional conductivity, environmental stability, and long cycle life. Additionally, epoxy resin (EP) is widely utilized in polymer coatings due to its strong adhesion to diverse substrates during curing. Here, we develop highly conductive and strongly adhesive PEDOT:PSS inks by combining PEDOT:PSS with EP using a composite engineering approach. These inks are used to fabricate PEDOT:PSS coatings by direct ink writing (DIW). We systematically evaluate the DIW of PEDOT:PSS-EP coatings, which show high electrical conductivity (ranging from 0.59 ± 0.07 to 41.50 ± 3.26 S cm⁻¹), strong adhesion (ranging from 15.84 ± 2.18 to 99.3 ± 9.06 kPa), and robust mechanical strength (8 MPa). Additionally, we examine the surface morphology, wettability, and hardness of the coatings with varying PEDOT:PSS content. The resultant coatings demonstrate significant potential for applications in antistatic protection, electromagnetic shielding, and other flexible electronic technologies. Full article

The aim of this study was to develop functional composite edible films or coatings for fruit preservation by the addition of bioactive components in combinations that have not yet been thoroughly studied, according to the relevant literature. Edible films were initially composed of (i) chitosan (CH), cellulose nanocrystals (CNC) and beta-cyclodextrin (CD) (50%-37.5%-12.5% ratio), and (ii) hydroxypropyl methylcellulose (HPMC), cellulose nanocrystals (CNC) and beta-cyclodextrin (CD) (50%-37.5%-12.5% ratio). The bioactive components incorporated (5, 10 and 15% v/v) were as follows: (i) pomace oil-based nanoemulsion (NE) aiming to enhance barrier properties, and (ii) caffeine (C), aiming to enhance the antioxidant activity of films, respectively. Indeed, NE addition led to very high barrier properties (low oxygen and water vapor permeability), increased flexibility and reduced color. Furthermore, the contribution of these coatings to fresh strawberries’ preservation under cold storage was investigated, with very promising results concerning weight loss, color difference, and preservation of fruit moisture and quantity of O₂ and CO₂ inside the packages. Additionally, C addition led to very high antioxidant activity, reduced color and improved barrier properties. Finally, the contribution of these coatings to avocado’s preservation under cold storage was investigated, with very encouraging results for color difference, hardness and peroxide value of the fruit samples. Full article

This paper describes studies on the preparation of an o–cresol–furfural–formaldehyde resin in the presence of an alkaline catalyst and its modification with n-butanol or 2-ethylhexanol. The novelty of this research is to obtain a furfural-based resin of the resole type and its etherification. Such resins are not described in the literature and also are not available on the market. The obtained resin based on furfural, which can be obtained from agricultural waste, had a low minimum content of free o–cresol < 1 wt.%, furfural < 0.1 wt.%, and formaldehyde < 0.1 wt.%. The resin structure was characterized by mass spectrometry (ESI-MS), FT-IR, and NMR spectroscopy, which showed the presence of hydroxymethylene groups in the resin before modification and alkyl groups derived from n-butanol and 2-ethylhexanol after modification. The etherified resins had a lower viscosity and were more flexible (DSC) than the resin before modification and they can be used as an environmentally friendly, safe, and sustainable alternative to traditional phenol–formaldehyde resins in the paint industry. They demonstrate the ability to create a protective coating with good adherence to metal substrates and an excellent balance of flexibility and hardness. Full article

Additive manufacturing (AM) or 3D printing of metals is gaining popularity due to its flexibility when fabricating parts with highly complex designs, as well as when simplifying manufacturing steps and optimizing process times. In this investigation, 17-4 PH stainless steel was additively manufactured using Laser Powder Bed Fusion (L-PBF), followed by functionalization through a DUPLEX treatment. This treatment involved a plasma-assisted nitriding process, followed by the deposition of an arc-PVD c-Al_0.7Cr_0.3N hard coating. The microstructural modifications resulting from plasma nitriding (such as the formation of Fe_2,3N and Fe₄N and the αN or expanded martensite phases) and the surface improvements with the c-Al_0.7Cr_0.3N coating on the 3D-printed 17-4 PH steel are evaluated in comparison to conventionally manufactured 17-4 PH steel. These microstructural characteristics are correlated with the mechanical response of the treated surfaces. As a result of the plasma nitriding process, the hardness of the 3D-printed 17-4 PH SS increased by approximately 260%. The wear, measured through dynamic and static scratch testing, was reduced by approximately 31%. This improvement was attributed to the modification of adhesive failure mechanisms, leading to a reduction in wear volume, improved coating adhesion, and enhanced scratch resistance. Full article

The low toughness of epoxy resin can influence its shielding performance against a corrosive medium and strength of adhesion to metal surfaces. Extensive efforts have been made to modify epoxy resin. In this research, acrylic resin was synthesized by the solution method, and 1 wt.%, 2.5 wt.%, and 5 wt.% were added to epoxy resin (E44 brand) to prepare coatings on the surface of AZ31B magnesium alloy. The effects of acrylic resin on the mechanical and protective properties of epoxy coatings were investigated via experiments measuring impact resistance, flexibility, and adhesion as well as the electrochemical impedance technique. Compared with the pure epoxy coating, the adhesion between the coating and the substrate increases by 1.37 MPa after the addition of 2.5 wt.% acrylic resin. Meanwhile, the pencil hardness has a slight change from 5B to 6B, and the flexibility significantly improves. Therefore, the epoxy coating exhibits enhanced anticorrosive properties after the addition of 2.5 wt.% acrylic resin. Full article

Using a stainless shadow mask combined with a magnetron-ion-assisted deposition (IAD) sputtering system, we investigate the surface morphologies and optical properties of microfilms. Optimal color-filter (CF) coating microfilms with niobium pent-oxide (Nb₂O₅)/silicon dioxide (SiO₂) multilayers on a hard polycarbonate (HPC) substrate, grown at 85 °C and 50 SCCM oxygen flow, can obtain a fairly uniform thickness (with an average roughness of 0.083 and 0.106 nm respectively for Nb₂O₅ and SiO₂ films) through all positions. On a flexible HPC substrate with the Nb₂O₅/SiO₂ microfilms, meanwhile, the peak transmittances measured in the visible range are 95.70% and 91.47%, respectively, for coatings with and without a shadow mask for this new-tech system. For the optimal CF application with a shadow mask, transmittance on each 100 nm band-pass wavelength is enhanced by 4.04% absolute (blue), 2.96% absolute (green), and 2.12% absolute (red). Moreover, the developed new-tech system not only enhances the quality of the films by achieving smoother and uniform surfaces but also reduces deposition time, thereby improving overall process efficiency. For the with-shadow-mask condition, there is little shift at 50% transmittance (T50%), and high transmittance (~97%) is maintained after high-temperature (200 °C) baking for 12 h. These results are well above the commercial CF standard (larger than 90%) and demonstrate reliability and good durability for flexible optical applications. Full article

The three-dimensional (3D) force sensor has become essential in industrial and medical applications. The existing conventional 3D force sensors quantify the three-direction force components at a point of interest or extended contact area. However, they are typically made of rigid, complex structures and expensive materials, making them hard to implement in different soft or fixable industrial and medical applications. In this work, a new flexible 3D force sensor based on polymer nanocomposite (PNC) sensing elements was proposed and tested for its sensitivity to forces in the 3D space. Multi-walled carbon nanotube/polyvinylidene fluoride (MWCNT/PVDF) sensing element films were fabricated using the spray coating technique. The MWCNTs play an essential role in strain sensitivity in the sensing elements. They have been utilized for internal strain measurements of the fixable 3D force sensor’s structure in response to 3D forces. The MWCNT/PVDF was selected for its high sensitivity and capability to measure high and low-frequency forces. Four sensing elements were distributed into a cross-beam structure configuration, the most typically used solid 3D force sensor. Then, the sensing elements were inserted between two silicone rubber layers to enhance the sensor’s flexibility. The developed sensor was tested under different static and dynamic loading scenarios and exhibited excellent sensitivity and ability to distinguish between tension and compression force directions. The proposed sensor can be implemented in vast applications, including soft robotics and prostheses’ internal forces of patients with limb amputations. Full article

The emergence of novel e-textile materials that combine the inherent qualities of the textile substrate (lightweight, soft, breathable, durable, etc.) with the functionality of micro/nano-electronic materials (conductive, dielectric, sensing, etc.) has resulted in a trend toward miniaturization, integration, and intelligence in new electronic devices. However, the formation of a conductive network by micro/nano-conductive materials on textiles necessitates high-temperature sintering, which inevitably causes substrate aging and component damage. Herein, a bis-hydroxy-imidazolium chloride salt as a hard segment to synthesize a waterborne polyurethane (WPU) adhesive is designed and prepared. When used in nano-silver-based printing coatings, it offers strong adherence for coatings, reaching 16 N cm⁻¹; on the other hand, the introduction of chloride ions enables low-temperature (60 °C) chemical sintering to address the challenge of secondary treatment and high-temperature sintering (>150 °C). Printed into flexible circuits, the resistivity can be controlled by the content of imidazolium salts anchored in the molecular chain of the WPU from a maximum resistivity of 3.1 × 10⁷ down to 5.8 × 10⁻⁵ Ω m, and it can conduct a Bluetooth-type finger pulse detector with such low resistivity. As a flexible circuit, it also offers high stability against washing and adhesion, which the resistivity only reduces less than 20% after washing 10 times and adhesion. Owing to the adjustability of the resistivity, we fabricated an all-textile flexible pressure sensor that accurately differentiates different external pressures (min. 10 g, ~29 Pa), recognizes forms, and detects joint motions (finger bending and wrist flexion). Full article