Search Results (210)

Epoxy resins are widely used as protective coatings in civil infrastructure, yet sulfate-rich environments accelerate their deterioration. This study evaluates the effectiveness of multi-walled carbon nanotubes (MWCNTs) in enhancing the sulfate resistance of epoxy resins. Neat and MWCNT-reinforced epoxy specimens (0.25 wt.% and 0.5 wt.%) were fabricated, heat cured at 100 °C and exposed to a solution of sulfuric acid and sodium chloride maintaining a pH of less than 3 for 0, 30, and 60 days. Analytical techniques, including scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS), revealed distinct degradation patterns: the neat epoxy exhibited puncture damage and extensive salt deposition, while the MWCNT-reinforced specimens showed crack propagation mitigated by nanotube bridging. Heat curing introduced micro-voids that exacerbated sulfate ingress. The salt deposition surged to 200 times for the MWCNT-reinforced specimens compared to the neat ones, whereas crack width was higher in the MWCNT reinforced specimen compared to their neat counterparts, given that crack-bridging was observed. These findings highlight the potential of MWCNTs to improve epoxy durability in sulfate-prone environments, though the optimization of curing conditions and dispersion methods is critical. Full article

In this work, the critical properties of epoxy resin reinforced with carbon-based nanoparticles were examined in order to improve its performance in protective coating applications. Epoxy resin composites with commercial multi-walled carbon nanotubes (MWCNTs) and graphene (GP) nanoplates were prepared via solution mixing. In addition, hybrid composites with 50:50 w/w MWCNTs/GP were also examined. The characterization of the EMI shielding effectiveness revealed that epoxy resin composites reinforced with MWCNTs presented the best performance. Composites with the same content of graphene exhibited much lower shielding results. As confirmed by electrical conductivity measurements, this outcome can be explained by the fact that the electrical percolation threshold in the composites reinforced with MWCNTs was met (around 5 phr), while the conductive network in the composites with graphene was not completely developed. An analysis of the mechanisms that contributed to EMI shielding for each type of specimen showed that, in the case of MWCNT composites, the main mechanism that determined the response of the material was reflection rather than absorption. It was also observed that by increasing the MWCNT content, the shielding efficiency of the composites was enhanced. In the case of graphene composites, the absorption and reflection remained at low levels, resulting in high transmission and therefore poor shielding. Regarding the examined hybrid composites (MWCNTs:GP at 50:50 w/w), it seemed that the MWCNT content determined their shielding performance. Full article

In this study, multi-walled carbon nanotubes (MWCNTs) were uniformly applied to polyethylene terephthalate (PET) film using a bar-coating method to fabricate conductive thin films, and their transmittance, surface morphology, and effects on the heating and electrical properties of cement composites were analyzed. The experimental parameters considered were the mixing method, MWCNT concentrations, use or absence of coating films, applied voltages, and electrode spacings. Considering these parameters, the cement composites were divided into a total of four groups and then fabricated. Group 1 is a method for fabricating plain cement composites (PCCs), while Group 2 is a method for fabricating PCC using only MWCNT-coated films. Group 3 is a method for fabricating PCC by adding only MWCNT dispersion, and finally, Group 4 is a method for fabricating PCC using both MWCNT dispersion and MWCNT-coated films. Furthermore, field emission scanning electron microscope (FE-SEM) image analysis confirmed that MWCNT were evenly distributed across the entire front surface of the PET film and formed a dense network structure. The experimental results of cement composites using these showed that when both MWCNT dispersion and MWCNT-coated films were used, the electrical resistance was significantly reduced and the heating performance was improved. In particular, when the electrode spacing was 40 mm and the applied voltage was 30 V, the MDCF-0.75 specimen exhibited the highest heating performance and the lowest electrical resistance. Full article

Diblock copolymers (BCP) consisting of poly(methyl methacrylate) (PMMA) and poly(1H,1H,2H,2H-perfluorodecyl methacrylate) (PsfMA) blocks are employed as templates for controlled dispersion and localization of multi-walled carbon nanotubes (MWCNT). Short MWCNT are modified with perfluoroalkyl groups to increase the compatibility between MWCNT and the semifluorinated (PsfMA) phase and to promote a defined arrangement of MWCNT in the BCP morphology. Thin BCP and BCP/MWCNT composite films are prepared by dip-coating using tetrahydrofuran as solvent with dispersed MWCNT. Atomic force microscopy, scanning and transmission electron microscopy reveal a strong tendency of the BCP to form micelle-like domains consisting of a PMMA shell and a semifluorinated PsfMA core, embedded in a soft phase, containing also semifluorinated blocks. MWCNT preferentially localized in the embedding phase outside the micelles. Perfluoroalkyl-modification leads to significant improvement in the dispersion of MWCNT, both in the polymer solution and the resulting nanocomposite film due to increased interaction of MWCNT with the semifluorinated side chains in the soft phase outside the micelle domains. As a result, reliable electrical conductivity is observed in contrast to films with non-modified MWCNT. Thus, well-dispersed, modified MWCNT provide a defined electrical conduction path at the micrometer level, which is interesting for applications in electronics and vapor sensing. Full article

Nanocomposite laminates containing carbon fibers, epoxy, and multiwalled carbon nanotubes were fabricated using a vacuum bag process. Ecofriendly ionic liquid (5 wt%)-treated multiwalled carbon nanotubes (pristine and nickel-coated) were added to the epoxy independently, in amounts ranging from 1 wt% to 3 wt%, in order to tailor the mechanical, electrical, and thermal performance of manufactured carbon fiber epoxy composite laminates. These nanocomposite laminates were later characterized through flexural testing, dynamic mechanical analysis, impedance spectroscopy, thermal conductivity tests, and FTIR spectroscopy to evaluate their suitability for battery pack applications. The findings showed that both types of multiwalled carbon nanotubes exhibited multifaceted effects on the properties of bulk hybrid carbon fiber epoxy nanocomposite laminates. For instance, the flexural strength of the composites containing 3.0 wt% of ionic liquid-treated pristine multiwalled carbon nanotubes reached 802.8 MPa, the flexural modulus was 88.21 GPa, and the storage modulus was 18.2 GPa, while the loss modulus peaked at 1.76 GPa. The thermal conductivity of the composites ranged from 0.38869 W/(m · K) to 0.69772 W/(m · K), and the electrical resistance decreased significantly with the addition of MWCNTs, reaching a minimum of 29.89 Ω for CFRPIP-1.5 wt%. The structural performance of hybrid nanocomposites containing ionic liquid-treated pristine multiwalled carbon nanotubes was higher than that of the hybrid nanocomposite of ionic liquid-treated Ni-coated multiwalled carbon nanotubes, although the latter was found to possess better functional performance. Full article

Maghemite nanoparticles (NPs) were successfully developed using phenolic-rich extracts (cyanidin) from Citrus reticulata peel residues. The 11 nm maghemite NPs, obtained at 3% w/v and at 353 K, presented the optimal synthesis conditions. To improve dye adsorption performance, the synergetic adsorption behavior between these 11 nm NPs and multiwall carbon nanotubes was demonstrated. Prior to the adsorption tests, the aging effect on NPs was carefully assessed using various analytical techniques, which clearly showed the magnetite–maghemite phase transition. However, this had no impact on the cyanidin coating or adsorption properties. A remarkable percentage removal of (93 ± 3)% for methylene blue and (84 ± 3)% for methylene green was achieved in short equilibrium times of 10 and 25 min, respectively, with an optimum pH value of 5.5. Reuse experiments revealed that 90% removal for both dyes was achieved between the second to seventh regeneration cycles. Organic loading during these cycles was effectively confirmed by X-ray photoelectron spectroscopy and magnetic measurements. Dye adsorption involves a two-step mechanism: (i) electrostatic adsorption by the negative surface groups of the adsorbent (isoelectric point of 5.2) and the dye cationic groups and (ii) π–π stacking interactions between the aromatic benzene rings of the dyes, the hexagonal skeleton of the multiwall carbon nanotubes, and the phenolic ring groups of the biosynthesized sample. These results suggest that the low-cost modified phenolic adsorbent can be successfully applied to dye removal from water with promising recycling properties. Full article

The limited mechanical properties of composite materials, including stiffness, strength, and biocompatibility, restrict their effectiveness in biomedical applications. This research enhanced the mechanical properties and biocompatibility of polylactic acid and carbon fiber-reinforced composites (PLA/CFRCs) by incorporating multi-walled carbon nanotube (MWCNT) fillers. The methodology involved synthesizing MWCNTs and integrating them into PLA/CFRC laminates using fusion-blending, dispersion, and interlaminar spray-coating. Raman spectroscopy confirmed the presence of MWCNTs, with characteristic D and G band peaks and an I_D/I_G of 1.44 ± 0.089. SEM revealed MWCNTs in the PLA/CFRC matrix and allowed size determination, with an outer diameter range of 125–150 nm and a length of 14,407 ± 2869 nm. FTIR identified interactions between the matrix and the MWCNTs, evidenced by band shifts. TGA/DSC analysis showed thermal stability above 338 °C for all composites. The tensile tests revealed that all composites had values greater than 19 GPa for the elastic modulus and 232 MPa for the ultimate strength. Cytotoxicity assays confirmed biocompatibility, and all samples maintained a cell growth rate greater than 80%. This study highlighted the potential of nanotechnology to optimize the mechanical behavior of polymer-based composites, expanding their applicability in biomedical fields. Full article

The rapid and timely evaluation of the mental health of emergency rescuers can effectively improve the quality of emergency rescues. However, biosensors for mental health evaluation are now facing challenges, such as the rapid and portable detection of multiple mental biomarkers. In this study, a non-invasive, flexible, wearable electrochemical biosensor was constructed based on the self-assembly of nanomagnetic beads for the rapid detection of cortisol in interstitial fluid (ISF) to assess the mental stress of emergency rescuers. Based on a one-step reduction, gold nanoparticles (AuNPs) were functionally modified on a screen-printed electrode to improve the detection of electrochemical properties. Afterwards, nanocomposites of MXene and multi-wall carbon nanotubes were coated onto the AuNPs layer through a physical deposition to enhance the electron transfer rate. The carboxylated nanomagnetic beads immobilized with a cortisol antibody were treated as sensing elements for the specific recognition of the mental stress marker, cortisol. With the rapid attraction of magnets to nanomagnetic beads, the sensing element can be rapidly replaced on the electrode uniformly, which can lead to extreme improvements in detection efficiency. The detected linear response to cortisol was 0–32 ng/mL. With the integrated reverse iontophoresis technique on a flexible printed circuit board, the ISF can be extracted non-invasively for wearable cortisol detection. The stimulating current was set to be under 1 mA for the extraction, which was within the safe and acceptable range for human bodies. Therefore, based on the positive correlation between cortisol concentration and mental stress, the mental stress of emergency rescuers can be evaluated, which will provide feedback on the psychological statuses of rescuers and effectively improve rescuer safety and rescue efficiency. Full article

Experimental investigations of the diode-laser-induced ignition of potassium picrate (KP) with a multi-walled carbon nanotube (MWNT) additive are presented in this article. KP/MWNT composites with varying contents were prepared directly by adding different quantities of MWNTs to a KP solution after the last synthesis step. Due to capillary action, the MWNTs homogeneously coated the surface of the KP, and some KP crystallized inside the MWNTs. The samples were characterized by scanning and transmission electron microscopy, differential thermal analysis, and laser ignition tests. At a constant laser power density, the doped KP showed a much shorter ignition delay time than the undoped KP (from 28.8 ms to 4.5 ms). Therefore, the higher the dopant MWNT ratio is, the shorter the ignition delay time is. Additionally, the more MWNTs are used to dope KP, the lower the required ignition power is. Full article

Silver nanoparticle-coated multi-walled carbon nanotube (Ag/MWNT) composites were prepared using a chemical plating method that effectively controls the overgrowth of silver nanoparticles, ensuring uniform particle size. Functionalization of the carbon nanotube surface with numerous functional groups facilitates the binding of silver ions to multi-walled carbon nanotubes (MWNTs). This process results in Ag/MWNT composites with a uniform distribution of silver nanoparticles, prepared through reduction via the silver mirror reaction. The impact of dispersants and reducing agents on the silver coating of carbon nanotubes was studied. The results revealed the formation of negatively charged functional groups (-COOH, -OH, -C=O, and -NH2) on the nanotube surface. These groups acted as nucleation sites for the formation of silver nanoparticles. These groups acted as nucleation sites for the formation of silver nanoparticles. Simultaneously, the Ag/MWNT composites demonstrated effective dispersion within the matrix, improving the electrical conductivity of the electronic paste by 32.1% and 33.1%. This improvement was attributed to the forming of a conductive pathway within the silver-modified composite. Ag/MWNT composites within the paste system improved interfacial contact between fillers and the matrix, enhancing their potential applications in thermal interface materials. Full article

Electromagnetic wave-absorbing materials (EMAMs) and structures are crucial in aerospace and electronic communications due to their ability to absorb electromagnetic waves. The development of materials that are lightweight, sustainable, and cost-effective, exhibiting high-performance absorption across a broad frequency spectrum, is therefore important. However, homogeneous electromagnetic absorbing materials require assistance to meet all these criteria. Therefore, developing multi-layer absorbing coatings is essential for enhancing performance. The present study uses 21 different composites of varying weight fractions of polypropylene, graphene nanoplatelets, and multiwall carbon nanotubes nanocomposites to develop multi-layer absorbing materials and optimize their performance. These multi-layer carbon polymer nanocomposites were meticulously constructed using evolutionary algorithms like Non-sorted Genetic Algorithm-II and Particle Swarm Optimization to achieve ultra-broadband electromagnetic wave absorption capabilities. Among the designed electromagnetic absorbing materials, a two-layer model, i.e., 1.5 wt% MWCNT/PP/epoxy with a thickness of 1.052 mm and 2.7% GNP/PP/epoxy with a thickness of 4.456 mm totaling 5.506 mm, was identified as optimal using NSGA-II. The structure has exhibited exceptional absorption performance with a minimum reflection loss of −21 dB and a qualified bandwidth extending to 4.2 GHz. PSO validated and optimized this structure, confirming NSGA-II’s efficiency and effectiveness in quickly obtaining optimal solutions. This broadband absorber design combines the structure design and material functioning through additive manufacturing, allowing it to absorb well over a wide frequency range. Full article

In this work, the synergistic effect of graphene nanosheets (GNs), as well as multiwalled carbon nanotubes (MWCNTs), as reinforcing agents of polydimethylsiloxane (PDMS) was investigated, in order to explore the possibilities of designing composite materials, tailored for use in the field of coatings, which might be, in fact, a very interesting application. It was shown that the addition of GNs and MWCNTs in PDMS matrices significantly improves the thermal stability of the obtained nanocomposites, especially those reinforced exclusively with GNs. The tensile tests indicated that strength increased for all the examined composites. It was also observed that the Young’s moduli had an increasing trend, with the exception of the composites containing only GNs, while those reinforced solely with MWCNTs exhibited the best performance. The O₂ permeability measurements revealed that the highest reduction in the permeability was observed in GN-MWCNT/PDMS composite membranes, in comparison to those reinforced only with graphene or carbon nanotubes. Dielectric relaxation spectroscopy showed that all the examined composites, and especially those of MWCNTs, possess electrical conductivity, apart from the samples reinforced exclusively with graphene. The electromagnetic shielding effectiveness was also improved at higher filler loadings, which is more evident in composites reinforced with MWCNTs. It was concluded that the improved properties of the above studied hybrid composites make them suitable for protective coating applications. Full article

Magnetite nanoparticles were synthesized using the green chemistry technique; ferric chloride was used as a precursor agent and Moringa oleifera extract was used as a stabilizer agent. A black powder, characteristic of magnetite, was obtained. X-ray diffraction was performed on the synthesis product and identified as magnetite (Fe₃O₄). Scanning electron microscopy characterization shows that nanoparticles have a spherical morphology, with sizes ranging from 15 nm to 35 nm. The synthesis of carbon nanotubes was carried out by the pyrolytic chemical deposition technique, from which multiwalled carbon nanotubes were obtained with diameters of 15–35 nm and of varied length. The decoration was carried out using the wet and sonification technique, where a non-homogeneous coating was obtained around the nanotubes. The thermal decomposition for both decorated and undecorated nanotubes presents two mass losses but with different slopes, where the activation energy for the decorated carbon nanotubes was 79.54 kJ/mol, which shows that the decoration gives more stability to the nanotubes since the activation energy of the undecorated nanotubes is 25.74 kJ/mol. Full article

Flexible pressure sensors based on paper have attracted considerable attention owing to their good performance, low cost, and environmental friendliness. However, effectively expanding the detection range of paper-based sensors with high sensitivities is still a challenge. Herein, we present a paper-based resistive pressure sensor with a sandwich structure consisting of two electrodes and three sensing layers. The silver nanowires were dispersed deposited on a filter paper substrate using the vacuum filtration coating method to prepare the electrode. And the sensing layer was fabricated by coating carbon nanotubes onto a mulberry paper substrate. Waterborne polyurethane was introduced in the process of preparing the sensing layers to enhance the strength of the interface between the carbon nanotubes and the mulberry paper substrate. Therefore, the designed sensor exhibits a good sensing performance by virtue of the rational structure design and proper material selection. Specifically, the rough surfaces of the sensing layers, porous conductive network of silver nanowires on the electrodes, and the multilayer stacked structure of the sensor collaboratively increase the change in the surface contact area under a pressure load, which improves the sensitivity and extends the sensing range simultaneously. Consequently, the designed sensor exhibits a high sensitivity (up to 6.26 kPa⁻¹), wide measurement range (1000 kPa), low detection limit (~1 Pa), and excellent stability (1000 cycles). All these advantages guarantee that the sensor has potential for applications in smart wearable devices and the Internet of Things. Full article

This study investigates the process of using multi-walled carbon nanotube (MWCNT) coatings to enhance lamp heating temperatures for solar thermal absorption applications. The primary focus is studying the effects of the self-organized honeycomb structures of CNTs formed on silicon substrates on different cell area ratios (CARs). The drop-casting process was used to develop honeycomb-structured MWCNT-coated absorbers with varying CAR values ranging from ~60% to 17%. The optical properties were investigated within the visible (400–800 nm) and near-infrared (934–1651 nm) wavelength ranges. Although fully coated MWCNT absorbers showed the lowest reflectance, honeycomb structures with a ~17% CAR achieved high-temperature absorption. These structures maintained 8.4% reflectance at 550 nm, but their infrared reflection dramatically increased to 80.5% at 1321 nm. The solar thermal performance was assessed throughout a range of irradiance intensities, from 0.04 W/cm² to 0.39 W/cm². The honeycomb structure with a ~17% CAR value consistently performed better than the other structures by reaching the highest absorption temperatures (ranging from 52.5 °C to 285.5 °C) across all measured intensities. A direct correlation was observed between the reflection ratio (visible: 550 nm/infrared: 1321 nm) and the temperature absorption efficiency, where lower reflection ratios were associated with higher temperature absorption. This study highlights the significant potential for the large-scale production of cost-effective solar thermal absorbers through the application of optimized honeycomb-structured absorbers coated with MWCNTs. These contributions enhance solar energy efficiency for applications in water heating and purification, thereby promoting sustainable development. Full article