Multi-walled Carbon Nanotubes Content Research Articles

Analysing the shape memory behaviour of MWCNT-enhanced nanocomposites: a comparative study between experimental and finite element analysis

Shape memory polymers (SMPs) are known for their unique ability to withstand large deformations and revert to their original shape under specific external stimuli. However, their broader application in biomedical and structural applications is restricted by limited mechanical and thermal properties. Introducing multi-walled carbon nanotubes (MWCNTs) into SMPs has proven to significantly enhance these characteristics without affecting their inherent shape memory features. This study investigates shape memory nanocomposites (SMNCs) through dynamic and thermogravimetric analyses, along with tensile, flexural, and shape memory testing, and explores fracture interfaces using scanning electron microscopy. Findings indicate optimal shape memory, thermal, and mechanical properties with 0.6 wt% MWCNT content, showcasing a shape recovery ratio of 93.11%, storage modulus of 4127.63 MPa, tensile strength of 55 MPa, and flexural strength of 107.94 MPa. Moreover, incorporating MWCNTs into epoxy demonstrated a reduction in recovery times by up to 50% at 0.6 wt% concentration. Despite a slight decrease in shape fixity ratio from 98.77% to 92.11%, shape recoverability remained nearly consistent across all samples. The study also introduces a novel finite element (FE) method in ABAQUS for modeling the thermomechanical behavior of SMNCs, incorporating viscoelasticity, validated by matching experimental results with FE simulations, highlighting its accuracy and practical applicability in engineering.

Mechanical improvement of carbon fiber/epoxy composites by sizing functionalized carbon nanotubes on fibers

AbstractA sizing agent mainly consisting of polyethersulfone and acidified multi‐walled carbon nanotubes (MWCNT) was developed for surface modification of carbon fibers (CF) to enhance the interfacial bond and to form carbon fiber‐carbon nanotube (CF‐MWCNT) multiscale reinforcements. To prepare the modified carbon fiber/epoxy resin composites (CFRP), a vacuum molding technique was used in this study. The effects of the MWCNT‐containing sizing agent on the morphology and chemical structure of the CF surface were observed by scanning electron microscopy and Fourier transform infrared spectroscopy. The influence of MWCNT length and content on the mechanical properties of CFRP were also studied. The experimental results showed that the strength of the CFRP decreased with the increase of MWCNT length, and the MWCNT with a content of 0.05 wt% had a good reinforced effect on the CFRP. After the sizing treatment, the interlaminar shear strength (ILSS) of the CFRP is increased. These enhancements are attributed to the improved mechanical bonding and chemical bonding between CF and resin matrix. The MWCNT provides nanosized rough surface to CF and these acidified MWCNTs attached to the surface of CF with polar oxygen‐containing functional groups improve the compatibility with reinforcement and resin matrix.Highlights Carbon fiber was modified by a sizing agent mainly consisting of polyethersulfone and acidified carbon nanotube (CNT). CNTs enhance the interfacial chemical bonding and mechanical bonding. The CNT length affects the mechanical properties of the carbon fiber/epoxy resin composites (CFRP). The modified carbon fiber has enhanced the mechanical properties of the CFRP.

Nerve tissue regeneration based on magnetic and conductive bifunctional hydrogel scaffold

The growth of neurons is often influenced by magnetic and electrical physical factors, and there is more and more research focused on designing a magnetic and conductive engineering scaffolds for nerve injury repair. In this study, electrospun poly lactic-co-glycolic acid (PLGA) fibers containing Fe3O4 magnetic nanoparticles were cryo-cut into magnetic short fibers (MSFs) and subsequently incorporated into sodium alginate (SA)/carboxymethyl chitosan (CMCS) hydrogel along with the addition of multi-wall carbon nanotubes (MWCNTs). MSFs can also achieve alignment by external magnetic fields within the hydrogel to construct magnetic and conductive bifunctional MSF/MWCNT/SA/CMCS hydrogel with anisotropic structure. The magnetic-conductive bifunctional hydrogel exhibited good magnetic responsiveness, electrically active and mechanical property, in which both conductivity and mechanical property increased with the enhancement of MWCNTs contents. Notably, appearing of aligned structure significantly promoted the mechanical property of MSF/SA/CMCS hydrogel. The MSF/SA/CMCS hydrogel with aligned structure also facilitated greater primary neuron cells proliferation than random ones. Compared with individual magnetic or conductive hydrogel, there was significant increase of cell viability in the primary cultured cortical neurons on MSF/MWCNT/SA/CMCS hydrogel with aligned structure. Simultaneously, electrical stimulation (ES) combined with magnetic stimulation (MS) delivered via magnetic and conductive bifunctional MSF/MWCNT/SA/CMCS hydrogel with aligned structure produced a better effect on promoting neuronal growth compared with individual ES or MS. Besides, hot plate measurement indicated that MSF/MWCNT/SA/CMCS hydrogel with aligned structure and MS significantly decreased the mice licking latency after sciatic nerve injury. Animal behavior studies confirmed the protective role of synergistic MS with magnetic hydrogel. Such hydrogel scaffolds have long term potential for nerve tissue regeneration.

Performance enhancement of nanofluid-based photovoltaic/thermal system with a novel finned multi-block container of phase change material in the summer season of northern India

This study describes the outdoor experiments conducted on a photovoltaic/thermal (PV/T) system during the summer months of May and June in the year 2023, in northern India. The main goal of this paper is to reduce the temperature of a photovoltaic (PV) module for effective thermal regulation by implementing a hybrid cooling strategy in a PV/T system. This is achieved by integrating two techniques: multi-walled carbon nanotubes (MWCNT)-water nanofluid as the working fluid for active cooling and paraffin wax as the phase change material (PCM) for passive cooling. Therefore, the present study aims to design, fabricate, and test an innovative thermal collector with a multi-block finned absorber plate positioned beneath the PV module to promote uniform heat transfer distribution and mitigate temperature stratification within each PCM block. The proposed PV/T-PCM system's performance is assessed from energetic, exergetic, economic, and environmental standpoints compared to the PV/T system and conventional PV module. The present study also examines the impact of different concentrations (0.1–0.2 %) of MWCNT and volumetric flow rates (0.5–1.5 l/min) of both water and nanofluids as heat transfer fluids. It is shown that a desirable flow rate of 1.5 l/min yields the most favorable outcomes. The PV/T-PCM (0.2 %) system has been found to exhibit the highest levels of energetic and exergetic electrical and thermal efficiencies, with reported values of 13.25 %, 65 %, 12.81 %, and 1.66 %, respectively. The economic assessment demonstrates that the proposed PV/T-PCM system, integrating water and nanofluid, results in cost savings of 17.41 % and 19.63 % compared to a traditional uncooled PV system. In the context of environmental sustainability, the highest net CO2 mitigation is estimated to be 18.01 tons for the nanofluid-based PV/T-PCM system. Thus, the results confirm that the proposed PV/T-PCM (0.2 %) system, incorporating a hybrid cooling technique, achieves optimal performance.

Tailoring surface properties of Poly(caprolactone)/Hydroxyapatite scaffolds through aminolysis and multi-walled carbon nanotube coating for bone tissue engineering

In this study, the effects of surface modification on the physicochemical properties, degradation behavior, and cellular responses of poly(caprolactone) (PCL)/hydroxyapatite (HAp) scaffolds using carboxylated multi-walled carbon nanotubes (MWCNTs) were investigated. The scaffolds were prepared using the fused deposition modeling (FDM) technique, followed by aminolysis for 15, 30, and 60 minutes. Subsequently, the scaffolds were immersed in MWCNT solutions with concentrations of 0.1 %, 0.5 %, and 1 % g/mL to achieve the desired coating. Various characterization techniques were employed to evaluate the surface morphology, chemical composition, and structural changes induced by the coating. FESEM images revealed a uniform MWCNT coating on the PCL/HAp scaffolds at an optimal concentration of 0.5 % g/mL, while lower concentrations resulted in incomplete coating and higher concentrations led to MWCNT agglomerations. The MWCNT coating successfully enhanced the conductivity of the scaffolds, with electrical conductivity increasing from near zero for the non-coated PCL/HAp scaffolds to 5 × 10−5 S/m for the MWCNT-coated scaffolds. Additionally, the coating exhibited improved wettability, as demonstrated by decreased water contact angles from 67.71° for non-coated surfaces to 51.50° for the MWCNT-coated surfaces. Furthermore, the in vitro degradation studies showed that HAp in the PCL matrix accelerated the hydrolysis rate, resulting in higher degradation rates for the PCL/HAp scaffolds than pure PCL scaffolds. The MWCNT coating further influenced the degradation behavior, with variations in degradation rates depending on the MWCNT concentration. Cell viability assays using MG-63 cells revealed improved cell viability and adhesion on the MWCNT-coated PCL/HAp scaffolds compared to plain PCL and PCL/HAp scaffolds. The cell viability increased from 84 % for plain PCL and 103 % for PCL/HAp to 109 % for the MWCNT-coated scaffolds. Moreover, FESEM images showed increased cell adhesion on the MWCNT-coated surfaces, with optimal adhesion observed on the scaffolds coated with 0.5 % g/mL MWCNTs. The results of this study highlight the potential of MWCNT coatings to improve the surface properties of PCL/HAp scaffolds, making them excellent choices for bone tissue engineering applications.

Self-sensing cementitious geocomposites in rail track substructures

A self-sensing cementitious geocomposite was developed based on laboratory data, and it demonstrated good physical and mechanical properties, durability, and piezoresistivity performance. It consisted of stabilized cemented sand containing multiwalled carbon nanotubes (MWCNTs) with graphene nanoplatelets (GNPs) as conductive fillers. This geocomposite could be used to detect damage based on the relationship between electrical impedance and mechanical performance, making it suitable for use as structural layers in railway lines. In this study, the effects of MWCNTs and GNPs, as well as of degree of saturation, were evaluated on the compaction, secant modulus, resilient modulus, electrical resistance, and piezoresistivity of the geocomposite. Scanning electron microscopy (SEM) and microscopic imaging were used to analyse microstructural alterations induced by varying concentrations of MWCNTs and GNPs. This innovative geocomposite, intended for installation in Portuguese railway lines as part of the EU project IN2TRACK3, is aimed at capturing performance data, identifying structural damage levels, and estimating load intensity, axle numbers, and train speed. The feasibility of its use is discussed based on literature studies and research conducted under the IN2TRACK2 and IN2TRACK3 projects, and its potential advantages over traditional methods for monitoring rail track health are highlighted.

Kinetics studies of CO2 hydrate formation in the presence of l-methionine coupled with multi-walled carbon nanotubes

In recent years, gas hydrate technology has been considered to be a promising method for CO2 capture and transport. Nevertheless, the development of the gas hydrate technology is hindered by the slow hydrate formation. In this work, the effects of concentration, initial pressure and gas-liquid ratio on the CO2 hydrate formation kinetics in the compound system of environmentally friendly additive l-methionine (L-met) coupled with low-dose multi-walled carbon nanotubes (MWCNTs) were investigated for the first time. The results showed that L-met coupled with MWCNTs could effectively promote the CO2 hydrate formation, and the promotion effect was related to the MWCNTs concentration. At 4.0 MPa, compared to the 0.1250 wt% L-met single system, the compound system with the MWCNTs concentration of 0.0270 wt%∼0.0720 wt% increased the CO2 gas consumption (Gsum) by an average of 6.37 %, and the induction time (tin) of CO2 hydrate formation were shortened by an average of 36.03 %. The optimal concentration of MWCNTs was 0.0450 wt%. Meanwhile, the increase of the pressure and gas-liquid ratio could effectively accelerate the kinetics of CO2 hydrate formation. The promotion effect of the pressure increasing was better than that of the gas-liquid ratio increasing. The pressure increasing could result in the maximum increase of 39.75 %, 122.83 %, and 69.85 % in Gsum, initial gas consumption rate (N10), and the gas to hydrate conversion (GTH), respectively; and the highest reduction of tin was 83.72 %. Furthermore, the hydrate morphological observations revealed that CO2 hydrate initially nucleated in the inner of L-met solution, and the hydrate particles in the compound system of L-met coupled with the MWCNTs were porous snowflakes. The wall climbing effect induced by capillary forces was further explained, and the presence of L-met enhanced the mass transfer capacity of CO2 hydrates. The practical use of fast hydrate formation technology for CO2 capture and sequestration has been facilitated by this work.

Investigating the valence balance of adding Nano SiC and MWCNTs on the improvement properties of copper composite using mechanical alloying and SPS techniques

This study presents a comprehensive investigation of copper-based nanocomposites reinforced with silicon carbide (SiC) nanoparticles and multi-walled carbon nanotubes (MWCNTs). The manufacturing procedure involved powder metallurgy techniques followed by spark plasma sintering (SPS). Microstructural analysis revealed a notable reduction in particle size (from 23.72 μm to 18.31 μm) and crystallite size (from 104.32 nm to 87.36 nm) with the addition of reinforcements. The bulk microstructure exhibited a reduction in grain size by approximately 13.1 %. XRD analysis confirmed the absence of new phases. Evaluation of SPS parameters demonstrated varying density and porosity, with the highest relative density of 99.96 % observed in pure copper composites. Hardness measurements indicated that surface hardness surpassed cross-sectional values, with the lowest recorded value being 64.79 HV for composite Cu-5%SiC-1%MWCNTs (S4). Wear rate analysis revealed an increase, with pure copper composites exhibiting a wear rate of 1.78 × 10^-4 mm3/m, while composite S4 displayed a rate of 3.25 × 10^-4 mm3/m under a load of 5 N. Coefficient of Friction (COF) exhibited significant fluctuations, influenced by the applied load and composite composition. Thermal conductivity decreased with higher SiC and MWCNT content, with sample S1 exhibiting the highest thermal conductivity among reinforced composites. Electrical conductivity trends were influenced by the type and concentration of reinforcing particles, resulting in an increase of approximately six times in composite S4 compared to the pure sample.

CoFe2O4/PANI/MWCNTs ternary hybrid composites. Synthesis, characterization, the effect of MWCNTs ratio and dye removal capability.

We have synthesized cobalt ferrite (CoFe2O4) using the sucrose auto-combustion method and subsequently employed the in situ polymerization technique to fabricate ternary composites comprising CoFe2O4, polyaniline (PANI), and multi-walled carbon nanotubes (MWCNTs). In this novel investigation, we explored the influence of varying MWCNTs ratios on these composites' structural, magnetic, thermal, and electrical properties. The crystal structures of the synthesized composites were analyzed using X-ray diffraction (XRD), while Fourier transform infrared (FT-IR) spectroscopy revealed changes in bonding patterns, including the disappearance of ferrite bonds and the emergence of new ones. Transmission electron microscopy (TEM) images illustrated a complete coating of PANI on both MWCNTs and CoFe2O4 particles, resulting in a substantial reduction in magnetization compared to pure CoFe2O4 ferrite due to PANI's nonmagnetic nature. Vibrating sample magnetometer (VSM) measurements confirmed this reduction, indicating a decrease to 7.3 emu.g-1. Thermal analysis demonstrated an enhancement in thermal stability with increasing MWCNTs content, as evidenced by an increase in the temperature equivalent for half decomposition (T50) from 486 to 522°C for composites with 40% MWCNTs. Moreover, the electrical conductivity showed a corresponding rise with MWCNTs content, increasing from 3.1 × 10-3 Ω-1.cm-1 to 2.2 × 10-2 Ω-1.cm-1, possibly indicating charge transfer from PANI to MWCNTs. To assess practical applications, we investigated the ability of the composite with 40% MWCNTs to remove phenol red (PR) dye from aqueous solutions. Through a systematic study of adsorption parameters and kinetics, we determined optimal conditions for effective dye removal and elucidated the underlying adsorption mechanism. Our results demonstrated the composite's efficiency in dye removal, with a 6.4mg·g-1 capacity for PR dye, highlighting its potential for environmental remediation efforts.

Development and modeling of an ultra-robust TPU-MWCNT foam with high flexibility and compressibility

Abstract Developing a cost-effective industrially scalable manufacturing method that can improve the mechanical properties of nanocomposite foams with higher flexibility, compressibility, and, at the same time, mechanically robustness is of significant interest. In this study, porous thermoplastic polyurethane (TPU)/multiwalled carbon nanotube (MWCNT) was fabricated with the chemical blowing agent (CBA) by a combination of compounding-compression molding methods. The effects of CBA and MWCNT contents on the foam morphology, porosity, foam cell size, Young’s modulus, and compressibility of fabricated samples were investigated. Through conducting cyclic compressive tests, it was observed that nanocomposite foams exhibited consistent mechanical responses across multiple compressive cycles and demonstrated notable characteristics, including high compressibility (up to 76.4% compressive strain) and high elastic modulus (up to 8.8 ± 2.6 MPa). Moreover, theoretical approaches were employed to predict the elastic modulus of solid and foam TPU/MWCNT. For solid MWCNT/TPU, a specific micromechanical model based on different modifications of the Halpin-Tsai (HT) approach was used, which showed a good agreement with experimental data at different MWCNT contents. Furthermore, the constant parameters of Gibson and Ashby’s method were found to successfully predict the elastic modulus of foam TPU/MWCNT at different MWCNT and CBA percentages.

Growth of MAPbI3 perovskite films on MWCNT-modified TiO2 thin films for solar cell applications

In this work, we have modified titanium dioxide (TiO2) films by incorporating multi-walled carbon nanotubes (MWCNTs) in TiO2-sol. TiO2 and MWCNT-modified TiO2 thin films have been prepared via solution processing spin coating route. Further, the structural, optical, and surface morphology of methyl ammonium lead iodide (MAPbI3) films have been studied onto pristine TiO2 and MWCNT-modified TiO2 films. We extensively analyze how different MWCNT concentrations impact the TiO2 and perovskite film structure, optoelectronic properties, and surface characteristics. The findings highlight that the MAPbI3 films maintain a tetragonal structure with enhanced crystallinity compact and smooth surface morphology in MWCNT-modified TiO2/MAPbI3 films. Besides this, enhanced optical absorbance in MAPbI3 films have also been observed on perovskite films fabricated onto MWCNT-modified TiO2 films with enlarged grains and a red shift in optical band gap has been observed for MWCNT-modified TiO2 films and MWCNT-modified TiO2/ MAPbI3 films. Further, various critical electrical parameters such as charge carrier concentration, Hall mobility, sheet resistance, and resistivity have been investigated to understand the effects of the incorporation of MWCNT on TiO2 films. The value of carrier concentration enhances from 3.76 × 1024 cm−3 to 6.39 × 1024 cm−3 on incorporation of MWCNT in TiO2 films. Furthermore, an enhancement in crystallinity, optical absorbance, and grain size has been observed in perovskite films fabricated onto TiO2/MWCNT films. Thus, TiO2 modification with MWCNT can tune the optical and charge transport properties of charge-transporting layer TiO2 films for perovskite photovoltaics and other optoelectronic devices.

Muti-Filler Composites Reinforced with Multiwalled Carbon Nanotubes and Chopped Carbon Fibers for the Bipolar Plate of Fuel Cells

To improve the conductivity and flexural strength of bipolar plates for proton-exchange membrane fuel cells, multi-filler-reinforced composites were prepared using graphite, multiwalled carbon nanotubes (MWCNTs), chopped carbon fibers (CCFs), and phenolic resin (PF). The effects of CCF content (0–6 wt.%) and MWCNT content (0–8 wt.%) on the flexural strength, electrical conductivity, interfacial contact resistance (ICR), density, hydrophobicity, and corrosion behavior of the composites were investigated. Results showed that the addition of a small number of CCFs (≤4 wt.%) effectively improved the flexural strength but slightly reduced the electrical conductivity and increased the ICR of the graphite/PF/CCF composites. Further addition of MWCNTs (≤6 wt.%) significantly improved the electrical conductivity and ICR of the graphite/PF/CCF/MWCNT composites, while maintaining high flexural strength. When the composites were filled with 4 wt.% CCFs and 2 wt.% MWCNTs, their electrical conductivity, flexural strength, ICR under 1.38 MPa, and contact angle were 272.8 S/cm, 43.1 MPa, 1.19 mΩ·cm2, and 101.5°, respectively. Compared to unreinforced composites, the electrical conductivity was reduced by 27.2%, the flexural strength was increased by 65.1%, and the composite possessed favorable hydrophobicity as well as corrosion behavior. This work reveals that CCFs and MWCNTs can effectively cooperate to improve composites’ electrical and flexural strength properties.

Experimental investigation and comparison of PBI/MWCNT and PSF/MWCNT membranes for recovering water from RO reject of brackish water by FO

The performances of polybenzimidazole (PBI) and polysulfone (PSF) membranes for recovering water from reverse osmosis (RO) reject of brackish water through forward osmosis (FO) were assessed and compared. Non-functionalised multi-walled carbon nanotubes (MWCNT) were added to the membrane casting solutions, with concentrations ranging from 0 to 3 wt%. The experiment was conducted for eight samples using RO reject of brackish water as the feed solution (FS) and 2 M analytical grade MgCl2 as the draw solution (DS). The hydrophilicity, water permeability, salt rejection rate (Rs), water flux (WF) and porosity of the membranes improved with increasing MWCNT content up to 2 wt%. Also, the structural parameter, salt permeability and reverse solute flux decreased. PBI/MWCNT2 wt% exhibited the best performance among the membranes tested compared with porosity of 70 ± 4 %, structural parameter of 0.36 ± 0.2 μm, and Rs of 93.5 %. In contrast with the pristine PBI membrane, an average water flux enhancement of 15 % and 49 % was observed for the FS and DS sides, respectively, for PBI/MWCNT2 wt%. It is evident from the results that including MWCNT improves the performance of both membranes, with better relative performance for PBI membranes than PSF membranes.

Post-creep residual tensile properties of multi-walled carbon nanotube/epoxy nanocomposites

Epoxy resin as a thermoset polymer is vulnerable to creep loading even at room temperature due to its viscoelastic nature. This study investigated the effect of reinforcing epoxy resin with different functionalized multi-walled carbon nanotubes (MWCNT) contents on the creep response and post-creep residual tensile properties of nanocomposites. The creep tests were performed on the nanocomposite specimens containing different filler contents and the neat epoxy specimen at 40°C under a constant load level of 200 N. It was found that the nanocomposites containing 0.3 wt% MWCNTs experienced 29.6%, 69.1%, and 74.1% decreases in the elastic strain, creep strain, and steady-state creep strain rate, respectively, compared to the neat epoxy. Furthermore, the tensile strength and stiffness of the neat epoxy and nanocomposite specimens were evaluated before and after a partial creep test (at a load level of 200 N for 150 min) by conducting tensile tests. The nanocomposites containing 0.3 wt% MWCNTs demonstrated considerable improvements of 35.9%, 41.2%, 27.9%, and 28.1% in strength, residual strength, stiffness, and residual stiffness, respectively, compared to the neat epoxy. Furthermore, scanning electron microscopy assessment was utilized to investigate the fracture surfaces of the nanocomposite specimens.

Low percolation threshold polyvinylidene fluoride/multi‐walled carbon nanotube composites: A perspective of electrical conductivity, crystalline, rheological and mechanical properties

AbstractRecently, conductive polymer‐based composites (CPC) have gained considerable interest for their outstanding processing, mechanical, electrical properties, and resistance tunability. Multi‐walled carbon nanotube (MWCNT) was introduced into polyvinylidene fluoride (PVDF) as the conductive filler via means of melt blending in this work. Effects of MWCNT on crystalline structure, thermodynamic behavior, electrical conductivity, processing and mechanical properties of PVDF/MWCNT were under investigation. By measuring the volume resistivity of PVDF/MWCNT, it was observed to have declined from 1.54 × 1012 to 3.71 × 101 Ω∙m with the MWCNT content changed from 0.7 to 1 vol%, which plummeted by 11 orders of magnitude. Therefore, it can be inferred that the percolation threshold of MWCNT lies within the range of 0.7–1 vol%. Additionally, the percolation threshold is obtained as 0.81 vol% by fitting using the percolation theory equation. Around the percolation threshold, PVDF/MWCNT composites exhibit negligible alterations in their rheological properties when contrasted with pure PVDF, yet their mechanical properties are improved. Furthermore, MWCNT does not substantially impact the crystalline structure and thermodynamic behavior of PVDF/MWCNT.Highlights The percolation threshold of MWCNT in PVDF is 0.81 vol%. The volume resistivity of the 1 vol% MWCNT sample was only 3.71 Ω∙m. 1 vol% MWCNT exhibit favorable rheological and mechanical properties.

The impact of synergistic action of methacrylic acid/zinc oxide/carbon nanotubes on metal Friction and wear

The continuous operation of essential refining equipment, internal mixers, leads to wear on their end faces, resulting in an increased gap between the mixer chamber and the end face. This, in turn, causes material leakage, reducing mixing efficiency and adversely impacting rubber performance. Therefore, investigating metal wear on the mixer's end face during the mixing process is essential. Scholars have introduced dynamic covalent bonds into rubber molecular chains, bestowing self-repairing capabilities upon the materials. This innovation has significant implications for extending rubber lifespan and lowering production costs. It involves adding methacrylic acid (MAA) and excess zinc oxide (ZnO) to construct an ionic crosslinking network, limiting covalent crosslinking of rubber molecules and enabling in-situ polymerization of MAA/ZnO, resulting in self-repairing properties. However, it is crucial to consider corrosive wear induced by MAA's strong acidity on metals. This study combines MAA, ZnO, and multi-walled carbon nanotubes (MWCNTs) through mechanical mixing to create a composite material called zinc methacrylate (ZDMA)/MWCNTs/rubber. The research investigates the in-situ synthesis mechanism of MAA and ZnO and the synergistic mechanism of ZDMA and MWCNTs. The study analyzes the impact of MWCNTs additive amount on the frictional wear of the internal mixer's metal end face. During the mixing process, ZDMA is grafted and polymerized onto rubber's macromolecular chains, forming ionic pairs with strong electrostatic interactions, creating a primarily reversible supramolecular network dominated by ion crosslinking. This ion crosslinking network, along with the three-dimensional mesh structure of MWCNTs, establishes a stable spatial structure within the rubber matrix. The study reveals that increasing the MWCNTs content to 3 phr reduces the aggregation of SiO2 particles and ZDMA granules within the rubber matrix, resulting in reduced friction coefficients, roughness, and wear rates of the metal. However, exceeding 3 phr of MAA content leads to excessive MWCNT aggregation within the rubber matrix, increasing wear rates, roughness, and friction coefficients due to hindrance of rubber macromolecular chain crosslinking and reduced SiO2 particle dispersion within the rubber matrix. These findings provide valuable insights into the dynamics of frictional wear in internal mixers.

Effects of PVA fibers and multi-walled carbon nanotubes reinforcement on uniaxial compression fatigue properties of Engineered geopolymer composites

As a new type of green and environmentally friendly cementing material, engineered geopolymer composites (EGC) have broad application prospects. In this study, uniaxial compression fatigue tests were conducted to investigate the fatigue properties of geopolymer material. A total of 137 samples were tested to investigate the effects of carbon nanotubes content, polyvinyl alcohol (PVA) fibers volume content, and maximum stress level on the fatigue life and deformation of geopolymers. The results showed that the fatigue life of geopolymers obeys Weibull distribution, and PVA fibers and multi-walled carbon nanotubes (MWCNTs) achieved multiscale enhancement of the fatigue life by up to 16.34 times. The total strain accumulation, residual strain, and fatigue stiffness of the geopolymers under fatigue loading exhibited a three-stage evolution rule, with stability within the secondary creep branch. In the process of EGC production, the innovative adoption of optimized MWCNTs surface modification and dispersion strategies improved the uniformity of MWCNTs distribution in the matrix. Scanning electron microscopy (SEM) confirmed the hybridization of MWCNTs and PVA fibers at the microscopic level, which can achieve multi-scale enhancement of geopolymers. This study successfully optimized the content of MWCNTs and PVA fibers, further expanding the application range of composite materials.

Layered co-continuous structure in bone scaffold fabricated by laser additive manufacturing for enhancing electro-responsive shape memory properties

Porous scaffold based on electro-responsive shape memory polymers (ESMPs) possesses great potential applications in minimally invasive surgery for bone defect repair because it provides the ability for remote control and internal heating. However, it's difficult to obtain co-continuous structure in bone scaffold for achieving excellent electro-responsive shape memory properties. In this study, layered co-continuous structure with thermoplastic polyurethane (TPU) loaded with multi-walled carbon nanotubes (MWCNTs) (referred to as cTPU) layer and l-polylactic acid (PLLA) layer alternate stacking was obtained via layer-by-layer fabrication technology, and the porous scaffold was fabricated via selective laser sintering (SLS). The thermal and electrical shape memory properties of the scaffolds with different contents of MWCNT were evaluated by dynamic mechanical analysis (DMA) and U-bending experiments. The results indicated that the layered co-continuous structure improved phase continuity and confined MWCNTs to one side, enhancing the electrically driven properties and shape memory properties. The scaffold with 1.5 wt% MWCNTs achieved shape fixed and recovery rates of 95.6% and 90.2%, respectively. With the further increasing of MWCNTs content, the shape memory properties decreased due to the agglomeration of MWCNTs in the cTPU phase, which affected the phase continuity of cTPU. The DMA results confirmed the good mechanical properties of the scaffold, and the cell culture experiment results demonstrated excellent cytocompatibility for cell attachment and growth. This work provides a feasible method to fabricate electro-responsive shape memory bone scaffold with layered co-continuous structure, which exhibits great potential in applications of bone defect repair.

Chloride penetration resistance of ultra-high performance concrete with various multi-walled carbon nanotubes

Ultra-high performance concrete (UHPC) with outstanding chloride penetration resistance (CPR) exhibits excellent prospects for extending the service life of structures in the marine environment. This study investigates the effects of various types and contents of multi-walled carbon nanotube (MWCNT) on the CPR of UHPC, including pristine MWCNT with different sizes, MWCNT with surface modification, and MWCNT with special structures. The results show that 0.25% thick-short pristine MWCNT, 0.5% short hydroxyl functionalized MWCNT, and 0.25% helical MWCNT show more significant enhancement effect, improving the CPR by 74.14%, 72.91%, and 77.17%, respectively. The correlation analysis results suggest a negative linear correlation between the CPR and pore volume of the composites. The C-S-H gels and small capillary pores with a diameter below 50 nm are the significant factors determining the CPR of the composites. This illustrates that the CPR enhancement effects of various types of MWCNT change with the refinement of pore structure of UHPC. The enhancing mechanisms can be attributed to the nano-core effects of MWCNT, reducing the CH crystal size and primary cracks, inhibiting the growth and propagation of microcracks, refining the pore structure, optimizing the compactness of the cement paste matrix and interfacial transition zone, thus reducing the channels for chloride ion diffusion, while increasing the constrictivity and tortuosity of the channels.

The dielectric properties of silicone-multiwall carbon nanotubes nanocomposite in the frequency range from 0.5 to 20 GHz

Integrating carbon nanotubes (CNTs) into a polymer matrix can significantly modify its physical properties, providing that the challenges associated with CNT dispersion are successfully resolved. In this work, we investigate the enhancement of the dielectric properties of silicone when multiwall carbon nanotubes (MWCNTs) are introduced to its polymer matrix as a filler in the frequency range from 0.5 to 20 GHz. An optimized procedure is used to prepare nanocomposites with MWCNTs concentrations by weight of 0%, 0.5%, 1.0%, 1.5%, and 2.0%. The investigated dielectric properties for the prepared nanocomposites are the real dielectric constant ɛ′, the imaginary dielectric constant ɛ″, the loss tangent tan δ, and the AC conductivity σAC. The dispersion of the MWCNTs in the silicone matrix is confirmed using the Fourier-transform infrared (FTIR) spectroscopy and the scanning electron microscope. This study shows that the dielectric properties of the nanocomposite are enhanced as the MWCNT’s concentration is increased over the entire frequency range. For example, the enhancement in ɛ′ value was from 3.2 up to 21.6 at 0.5 GHz and from 2.5 to 10.6 at 20 GHz as the concentration increased from 0% to 2.0%. For the ɛ″ value, the enhancement was from less than 0.1 to 8.6 at 0.5 GHz and to 2.0 at 20 GHz, respectively. Based on the obtained tanδ values, the nanocomposites with MWCNTs of 0.5% and 1.0% can be classified as low-loss dielectrics, while the other nanocomposites with MWCNTs of 1.5% and 2.0% are classified as lossy dielectrics.