High Concentration Of Carbon Nanotubes Research Articles

3D printable carbon nanotubes-based composites with reconfigurable shapes and properties

In this work, we developed an efficient approach to fabricating composites of carbon nanotubes (CNT) with shape reconfiguration ability and Joule heating behavior by incorporating the direct ink writing (DIW) technique. Our 3D printable ink consisted of a high concentration of CNT stabilized by polyvinylpyrrolidone (PVP) in an aqueous polyvinyl alcohol (PVA) solution. The rheology of the ink was tuned by the amounts of CNT and PVP. The printed objects underwent the freeze-thaw process to form weak hydrogels induced by the crystallization of PVA. Subsequently, the hydrogels were immersed in a deep eutectic solvent (DES) bath consisting of choline chloride and glycerol. This process replaced the water in the hydrogels with DES and led to mechanically tough DES/CNT gels. We utilized the high stretchability of DES/CNT gel to achieve complex geometries that would be challenging to accomplish solely with DIW. After reshaping the DES/CNT gels, the target shape was fixed by further solvent exchange with ethanol and drying. The final CNT composites showed a high electric conductivity of up to 33.94 S/m and exhibited remarkable Joule heating performance using a low applied voltage (5 V). Additionally, we successfully achieved a spatial variation of mechanical stiffness, electrical conductivity, and Joule heating across the printed objects by a selective solvent removal process. In short, this work expands the scope of possible shapes and properties of CNT-based composites.

Coarse-grained modeling of polystyrene-modified CNTs and their interactions with lipid bilayers

In the present work, we describe Martini3 coarse-grained models of polystyrene and carboxyl-terminated polystyrene functionalized carbon nanotubes (CNTs) and investigate their interactions with lipid bilayers with and without cholesterol (CHOL) using molecular dynamics simulations. By changing the polystyrene chain length and grafting density at the end ring of the CNTs at two different nanotube concentrations, we observe the translocation of nanoparticles as well as changes in the lipid bilayer properties. Our results show that all developed models passively diffuse into the membranes without causing any damage to the membrane integrity, although high concentrations of CNTs induce structural and elastic changes in lipid bilayers. In the presence of CHOL, increasing CNT concentration results in decreased rates of CHOL transmembrane motions. On the other hand, CNTs are prone to lipid and polystyrene blockage, which affects their equilibrated configurations, and tilting behavior within the membranes. Hence, we demonstrate that polystyrene-functionalized CNTs are promising drug-carrier agents. However, polystyrene chain length and grafting density are important factors to consider to enhance the efficiency of drug delivery.

Scalable production of high-quality carbon nanotube dispersion in aqueous solution using cellulose as dispersant by a freezing/thawing process

Carbon nanotube (CNT) dispersion, which enables scalable fabrication of printed and flexible electronic materials, has brought a revolutionary improvement in CNT-based devices. To progress from the laboratory to commercial applications, it will be necessary to develop simple and scalable methods to produce high-quality CNT dispersions. Here, we propose a freezing/thawing strategy assisted by cellulose to produce high-quality CNT dispersion in an aqueous solution on a large scale. The freezing/thawing process simultaneously serves two purposes: (1) one is to cleave CNTs from their bulk via water-freezing expansion force; (2) the other is to dissolve cellulose in NaOH/urea aqueous solution, facilitating the wrapping of cellulose on the surface of CNTs to improve the stability of the dispersion. The obtained cellulose-dispersed CNT (CDCNT) dispersion is highly homogeneous and stable because of the formation of CNT/cellulose/NaOH/urea inclusion complexes. Importantly, the freezing/thawing strategy using cellulose promises scalable production, including a high CNT concentration of 11.3 mg/mL, high yield of 75%, high production capacity, and unlimited system size, much superior to common ultrasonication. Furthermore, it is demonstrated that the CDCNT dispersion can be used as a precursor solution for fabricating different CNT-based materials via various techniques, such as spinning, dyeing, screen printing, and 3D printing, indicating versatile applications.

Experimental evaluation of carbon/epoxy laminates with concentrated carbon nanotube interlayers for high damping

Carbon nanotubes (CNTs) embedded in carbon/epoxy (c/ep) composites offer a lightweight, stiff solution with high damping for structural components. To manufacture CNT/c/ep hybrid composites with high concentrations of CNTs, a CNT yarn interlayer concept is used. Through a mechanism known as stick-slip, the interface between CNTs and c/ep laminates dissipate energy during dynamic cycling. It is predicted that altering the interfacial bond strength can enhance dynamic properties: loss factor, loss modulus, and storage modulus. In this research, the effect of surface treatments on CNT yarns prior to inserting the CNTs into the laminate was explored to determine if the dynamic properties of the composite were enhanced. It was determined that 2,3-dibromo-1,4-butanediol (23D14B), Triton X-100 (TX) and a solution of sulfuric and nitric (S/N Acid) were the best treatments of 12 tested based on the increased dynamic properties. For a composite with 5 vol% CNT yarn interlayers, 23D14B, TX, and S/N Acid increased Loss Factor by 230%, 130%, and 160%, respectively. Elevated temperature, moisture-saturated/elevated temperature, and cyclic loading frequency were investigated on 5vol. % CNT interlayers to determine their effects on dynamic properties of the CNT hybrid composites.

Flexible Electronics: Substrate‐Versatile Direct‐Write Printing of Carbon Nanotube‐Based Flexible Conductors, Circuits, and Sensors (Adv. Funct. Mater. 25/2021)

In article number 2100245, Crystal E. Owens, Gareth H. McKinley, A. John Hart and co-workers present a direct-write printing process controlled by two parameters to extrude aqueous carbon nanotube (CNT) solutions with liquid crystalline behavior, drawing highly conductive and flexible traces, sensors, and circuits with integrated circuit elements onto a variety of flexible substrates. The high CNT concentration and lack of fillers allow high final conductivity.

Insights into the mechanism of multi-walled carbon nanotubes phytotoxicity in Arabidopsis through transcriptome and m6A methylome analysis

With the increasing production and wide application of carbon nanotubes (CNTs), they are inevitably released into the natural environment and ecosystems, where plants are the main primary producers. Hence, it is imperative to understand the toxic effects of CNTs on plants. The molecular mechanisms underlying the toxic effects of CNTs on plants are still unclear. Therefore, in the present study, we investigated the effects of high concentrations of multi-walled CNTs (MWCNTs) on Arabidopsis. Root elongation and leaf development were severely inhibited after MWCNT exposure. Excess production of H2O2, O2−, and malondialdehyde was observed, indicating that MWCNTs induced oxidative stress. The antioxidant system was activated to counter MWCNTs-induced oxidative stress. Combinatorial transcriptome and m6A methylome analysis revealed that MWCNTs suppressed auxin signaling and photosynthesis. Reactive oxygen species metabolism, toxin metabolism, and plant responses to pathogens were enhanced to cope with the phytotoxicity of MWCNTs. Our results provide new insights into the molecular mechanisms of CNT phytotoxicity and plant defense responses to CNTs.

Constructing a Microcapacitor Network of Carbon Nanotubes in Polymer Blends via Crystallization-Induced Phase Separation Toward High Dielectric Constant and Low Loss.

Tailoring the distribution of nanoparticles and further constructing effective microcapacitors in polymer blends are important issues for developing high-performance polymer dielectric nanocomposites. The common method to control the selective localization of nanoparticles in an immiscible polymer blend is relatively difficult and it easily results in the accumulation of nanoparticles in one component, which usually leads to a dramatic increase of the dielectric loss in the nanocomposites. In this work, a novel strategy based on step-by-step crystallization has been proposed to tailor the refined distribution and dispersion of carbon nanotubes (CNTs) in a melt-miscible blend poly(butylene succinate)/poly(vinylidene fluoride) (PBS/PVDF) through the crystallization-induced phase separation and the engineered interfacial affinity between CNTs and polymer components to acquire high dielectric constant and low dielectric loss. The results reveal that PBS is excluded along the growth front of PVDF spherulites and locates in the margin areas of PVDF spherulites during the step-by-step crystallization process. Moreover, because of the higher interfacial interaction between CNTs and PBS, CNTs are located in the PBS-rich domain, resulting in a high concentration of CNTs in the interspherulites of PVDF. Thus, the dielectric constants of the nanocomposites are greatly improved by nearly 5-24 times compared with the nanocomposites achieved by quick cooling and, simultaneously, the dielectric loss of the nanocomposites is still maintained at a low level. This work shows that the step-by-step crystallization method can be used to fabricate the nanocomposites with a synergistic increase in the dielectric performance due to the formation of a refined microcapacitor assembly. To the best of our knowledge, this is the first report to show that the dielectric constant of the nanocomposites can be greatly enhanced just through the crystallization-optimized distribution and dispersion of CNTs in immiscible polymer blends, and it possibly gives a new technical route for the fabrication of advanced dielectric composites.

Interphase thickness and electrical conductivity of polymer carbon nanotube (CNT) nanocomposites assuming the interfacial conductivity between polymer matrix and nanoparticles

The interphase thickness in polymer carbon nanotube (CNT) nanocomposites (PCNT) is expressed by CNT characteristics and interfacial conductivity between CNT and polymer matrix. Also, the effective length and concentration of CNT are defined supposing interfacial conductivity to suggest the percolation threshold and the fraction of networked CNT. Furthermore, a simple model is developed to predict the conductivity of PCNT assuming tunneling effect, interphase region and interfacial conductivity. The influences of all parameters on the interphase thickness, percolation threshold, the fraction of networked CNT and the conductivity of PCNT are studied. In addition, some experimental results are provided to compare the predictions of developed model to the experimental measurements. The high levels of CNT radius, CNT length, CNT conductivity, interfacial conductivity and conductivity transferring can produce a thick interphase, but the waviness cannot change it. Moreover, the developed model can properly calculate the conductivity of studied samples. A desirable conductivity is obtained by thin and long CNT, medium CNT conductivity, poor waviness, high interfacial conductivity and good conductivity transferring, because they provide high effective CNT concentration and low percolation threshold in nanocomposites.

Energy dissipation characteristics of additively manufactured CNT/ABS nanocomposites

PurposeThis study aims to discuss the effect of carbon nanotubes (CNTs) on the mechanical properties of acrylonitrile–butadiene–styrene (ABS) composites fabricated by additive manufacturing (AM). Insight into the energy-dissipation mechanisms introduced and/or enhanced by the addition of CNTs is presented in this study.Design/methodology/approachABS/CNT filaments were fabricated with different concentrations of CNTs. Using a fused deposition modeling approach, unidirectional specimens were printed using a MakerBot Replicator 2X (MakerBot Industries, Brooklyn, NY, USA). Specimens were tested under static and dynamic conditions, with the loading coinciding with the printing direction, to determine elastic modulus, strength and viscoelastic properties.FindingsA CNT reinforcing effect is evident in a 37 per cent increase in elastic modulus. Likewise, the strength of the composite increases by up to 30 per cent with an increase in weight fraction of CNTs. At low dynamic strain amplitudes (0.05 per cent), a correlation between dissipated strain energy of the butadiene phase and strength of the composite is found such that less dissipation, from constraint of the butadiene particles by the CNTs, leads to higher strength of the composite. At higher dynamic strains, the presence of a high concentration of CNT leads to increased energy dissipation, with a maximum measured value of 24 per cent higher loss factor compared to baseline specimens. Because the trend of the composite behavior is similar (with a higher absolute value) to that of neat ABS, this study’s results indicate that well-established polymer/CNT dissipation mechanisms (such as stick-slip) are not significant, but that the CNTs amplify the dissipation of the ABS matrix by formation of crazes through stress concentrations.Originality/valueThis study provides knowledge of the dissipation behavior in additively manufactured ABS/CNT composites and provides insight into the expansion to new printable materials for dynamics applications.

Condition monitoring of crack extension in the reinforcement adhesive joints by carbon nanotubes


 
 
 Carbon nanotubes (CNT) are ideally suited to be employed for damage sensing in fiber rein- forced composite structures. In this work, the capability of CNTs for crack extension of a single lap Al-Al adhesive joints (SLJ) under shear load is studied using electrical resistance change. Different weight per- cent of CNT are added to epoxy adhesive. Epoxy adhesive with high concentration of CNT is obtained during shear loading to have the maximum strength and provide the best sensory properties. To provide a more concise evaluation of the crack extension in the adhesive layer under shear load, artificial defects are embedded into the SLJ specimens. The effects of square and circular defects with two different sizes on the crack extension in the adhesive layer are evaluated. The results showed that the maximum relative resistance change has occurred by 220% when the microcracks are initiated and accordingly developed from the nanoadhesive and changed its direction from the Square defect boundary. Additionally, in comparison with interface fracture in defective adhesive joint, when a part of crack grows through the adhesive layer, the resistance change showed higher values.
 
 

Mode II interlaminar fracture toughness of carbon nanotubes/epoxy film-interleaved carbon fiber composites

In recent years, the demand for composite materials in various industries such as aerospace, defense, and automotive industries has increased significantly. Furthermore, the mechanical properties of carbon fiber-reinforced plastic (CFRP) composites have been improved significantly. However, the out-of-plane (thickness direction) mechanical properties of CFRP laminates are considerably inferior to their in-plane mechanical properties. Owing to their unique properties, carbon nanotubes (CNTs) have been used to improve the mechanical properties of CFRP composites. However, it is challenging to disperse high concentrations of CNTs in the polymer resin matrices of such composites. In this study, a high concentration of CNTs was incorporated in CFRP laminates in the form of CNT/epoxy films by using ultrasonication and three-roll milling. Furthermore, unidirectional and plain woven prepregs were used for reinforcement. The mode II interlaminar fracture toughnesses of the CNT/epoxy film-interleaved CFRP composites with different CNT concentrations were measured by carrying out their end-notched flexure (ENF) tests. Optical micrographs were obtained to observe the microstructures of the specimens with different CNT loadings. The fracture surfaces obtained after the ENF tests were examined using a scanning electron microscope to investigate the toughening mechanism of the composites.

3D-Printed Scaffolds with Reinforced Poly (Lactic Acid)/Carbon Nanotube Filaments Based on Melt Extrusion

Personalized medicine suitable for individual patients in tissue engineering is a significant challenge. Owing to the recent growth of 3D printing, various methods of building objects have been proposed. However, there is very little information about the mechanical properties of the pieces obtained by controlling the process variables using composite filaments. Fused deposition modeling (FDM) technology was used to fabricate new scaffolds with infill patterns, interconnected channel networks, controllable porosity, and size. Polylactic acid (PLA)/carbon nanotube (CNT) filaments were synthesized using the melt extrusion technique. An improvement in the mechanical properties was observed in composites compared with the pure polymer. Moreover, no toxicity was expressed by stem cells after 24 h of incubation in the presence of composite filaments for a high CNT concentration. Our results will aid in the scaffold design of composite filaments through the modeling of process parameters and mechanical properties.

Structure and rheological behavior of polypropylene interphase at high carbon nanotube concentration

The structure of the interphase in polypropylene (PP)/multiwall carbon nanotube (MWNT) nanocomposite was characterized by thermal analysis and wide angle X-ray diffraction. The interphase was composed of non-covalently coated PP on acid functionalized MWNT (f-MWNT), where the volume of interphase increases with increased f-MWNT concentration from 1 wt% to 30 wt%. Larger lamella thickness, crystallinity, and smaller crystal size with respect to the bulk polymer were found at the interphase. Also, the thermal stability of the nanocomposite containing high volume fraction of interphase was demonstrated to be higher than that of the neat PP. Using designed thermal treatment, the interphase was successfully converted into a highly ordered crystalline structure with extended chain conformation. The understanding and control over the interphase formation at nanoscale afforded the observation of an unprecedented macroscopic rheological behavior where the viscosity and elastic modulus increased as temperature increased. A schematic showing polymer-CNT interaction at elevated temperature was proposed and verified. It is concluded that the constrained flow under high temperature originates from extended and immobile polymer chains at the interphase.

Plant and Microbial Growth Responses to Multi-Walled Carbon Nanotubes

Carbon nanotubes, made of graphene, one of the world’s strongest material, has shown properties that are used in applications such as energy storage devices, electron emission devices, and environmental engineering application. Recently, researchers have focused on determining the effects of carbon nanotubes on soil microorganisms and plants.Objective: The purpose of this study was to determine if the multi-walled carbon nanotubes will affect the growth of Phaseolus vulgaris as well as inhibit the growth of select soil microbes.Methods: The effects of Multi-Walled Carbon Nanotubes were determined on bean plants grown under hydroponic conditions and on select soil microbes. Two weeks after germination, the plants were exposed to different concentrations of dispersed multi-walled carbon. The different concentrations were 0 ug (control), 50 μg, 250 μg, 500 μg, 750 μg and 1000 μg mLˉˡ. The growth was reported weekly by measuring the plants themselves, the diameter of the leaf, length and width, the roots, and the fruits. Cultures of Mesorhizobium sp. and Nitrosomonas stercoris were exposed to the 0 μg (control), 50 μg, 250 μg, 500 μg, 750 μg and 1000 μg mLˉˡ of dispersed MWCNTs then incubated in the BioScreen reader. The optical density was reported every 30 minutes for 24 hours.Results: Our results showed that at 50 μg/mL, bean plants exhibited tolerance to the multi-walled carbon nanotubes whereas at 250 μg/mL and 500 μg/mL of MWCNTs plants showed reduced growth and development and even plant death. Aliquots of 750 μg/mL and above of MWCNTs lowered the microbial biomass. The presence of high concentrations of carbon nanotubes is likely to cause stress to microbes and the direct contact of CNTs with microbes could damage their cell membrane leading to cell death.Conclusion: As results of this study, the concentration of multi-walled carbon nanotubes should be set at a maximum of 500 μg mLˉˡ when being released to the soil or environment.

Rheological behavior of mechanically stabilized and surfactant-free MWCNT-thermal oil-based nanofluids

The viscosity of nanofluids is one of the important parameter for the design of heat transfer processes. The evolution of usage of nanofluids in heat transfer processes is gaining more industrial consideration due to excellent thermal properties. However, limited attention is focused on the rheological behavior of nanofluids as of today. The multiwall carbon nanotubes (MWCNTs) are stabilized in thermal oil using ultrasonication and high stability is observed. The rheological behavior of thermal-oil based dispersant-free nanofluids are studied at varying high shear rates (100–2000s−1), temperatures (25–90°C) and nanoparticle concentrations (0.1–1wt%). The effect on the shear stress and viscosity by the addition of carbon nanotubes in thermal oil is discussed. The measured effective viscosity is compared with different theoretical conventional models. A significant increment in relative viscosity is observed at high concentrations of carbon nanotubes. A correlation is developed based on the temperature, nanomaterial concentration, and shear rate.

Significantly Increased Solubility of Carbon Nanotubes in Superacid by Oxidation and Their Assembly into High‐Performance Fibers

This study demonstrates that small amount of oxygen incorporated into carbon nanotubes (CNTs) during the purification process greatly increases their solubility in chlorosulfonic acid (CSA). Using as-purchased and unpurified CNT powders, the optimal purification process is established to significantly increase the solubility of CNTs in CSA, and spin CNT fibers with high mechanical strength (0.84 N tex-1 ) and electrical conductivity (1.4 MS m-1 ) from the CNT liquid crystal dope with high concentration of CNTs in CSA. The knowledge obtained here may guide development of a way to dissolve extremely long CNTs at high concentration and thereby to enable production of CNT fibers with ultimate properties.

Fabrication and toughening behavior of carbon nanotube (CNT) scaffold reinforced SiBCN ceramic composites with high CNT loading

Abstract Uniform dispersion, high loading and three-dimensional (3D) continuous network of carbon nanotube (CNT) are desired for high-performance nanocomposites to fully utilize the superior strength and toughness of CNTs. In this work, monolithic CNTs/SiBCN composites with high CNT loading (10 wt% and 20 wt%) were prepared from 3D scaffold-like CNT cottons and a liquid polyborosilazane (PBSZ) precursor through precursor infiltration and pyrolysis process. The 3D CNT scaffold in the nanocomposite can function as passive filler and gas path to ensure formation of monolithic bulks. Moreover, direct infiltration of PBSZ into the pores among CNT cotton can hinder agglomeration of CNTs and localize CNTs at the original sites, guarantee good alignment and high CNT concentration in the final nanocomposite. This highly concentrated 3D CNT reinforcement in the nanocomposite shows unique resistance to cracking under external stress related to the complex fracture behavior of CNT bundles during the cracking formation and extension process (including CNT bridging, aligning, pulling out and then breaking), which more favors for absorbing energies and enhance toughness of the ceramic composites.

Microfabrication with smooth thin carbon nanotube composite sheets

Carbon nanotube (CNT)/polymer composite materials can be high strength, stiff, and lightweight, which makes them attractive for fabrication of micromechanical structures. Here we demonstrate a method whereby smooth, thin, high CNT concentration composite sheets can be fabricated and patterned on the microscale using a process of photolithography and plasma etching. Two types of CNT/polymer composite sheets were fabricated: one made from CNTs grown on patterned supported catalyst and one made from CNTs grown with floating catalyst; these had thicknesses of 6 µm and 26 µm respectively and a roughness of less than 60 nm.

Changing liquid crystalline phase with field

ABSTRACTSince 1888, the liquid crystal display (LCD) industry is facing a fierce competition due to serious limitations such as poor contrast ratio and response time. Although some new materials have offered new applications and opened new markets for LCDs, materials with improved contrast ratio are highly desirable in LCD industry to sustain in the current market. This work reports a new behaviour in nano-material-doped liquid-crystal composite which is suitable for eradicating limitations of contrast ratio. Here, a high concentration of carbon nanotubes (CNTs) is doped in liquid crystal (LC) materials wherein the CNTs form aggregates in the LC composition. In these heavily doped samples, the phase change takes place with application of bias. This reversible process improves the contrast ratio as the material oscillates between crystalline and LC phases with field.

Field dependence of liquid-crystalline phase in liquid-crystal and carbon nanotubes composite

ABSTRACTDue to their exceptional properties, liquid crystals are useful for a wide range of applications. As reported in the literature, a slight dispersion of liquid crystals with carbon nanotubes has a detectable effect on the liquid-crystal properties making them appropriate for various applications. The present work reports a new application of these composites disclosing a process of transformation of commercially available high-temperature liquid crystals into low-temperature liquid crystals. This is accomplished by using high concentration of carbon nanotubes in liquid-crystal materials wherein the carbon nanotubes form cluster inside the liquid-crystal cells. The application of bias on these heavily doped samples resulted in the appearance of liquid-crystal phases at room temperature which, in the case of pure liquid crystals, were observable only at high temperature. The process is reversible and hence phase change can be controlled by external field.