Well-dispersed Carbon Nanotubes Research Articles

Constructing the charge channel with CFx using a well-dispersed carbon nanotube arrays to boost high-rate primary battery

Pursuing ultra-high specific energy density for lithium fluorinated carbon (Li/CFx) battery requires a high fluorine to carbon ratio, resulting in low-conductivity and surface-polarization issues, which restricts battery of high-rate performance. Herein, the rich charge transport channels among CFx were constructed using a well-dispersed and highly-oriented carbon nanotube arrays (CNTA) to enhance high-rate performance in Li/CFx battery. The advantage of high-orientation lies in maintaining the appropriate van der Waals forces of this CNTA prepared by catalytic chemical vapor deposition (CCVD), which helps to avoid carbon nanotubes (CNT) entanglement and achieves good dispersion. Compared with conductive additives of commercial carbon nanotubes (CCNT) and super-P (CSP), CNTA effectively releases CFx surface-polarization favouring to Li+ diffusion. Therefore, battery performance was enhanced with reduced voltage delay and low impedance. At a discharge rate of 5 C, the Li/CFx battery using CNTA had a specific capacity of 697.32 mAh/g, while these batteries using CCNT and CSP lost discharge-performance. This highly-oriented CNTA enriches the conductive additives system of lithium primary batteries and provides a novel pathway for suppressing CFx polarization.

Conductive copper ion-reinforced sodium alginate aerogel based free-standing Si anode for Li-ion storage

Biomass materials with great advantages of wide accessibility, low cost and environmental benignity have favorable application prospects as Si anodes for lithium-ion batteries (LIBs). In order to alleviate the volume effect and improve the conductance of Si, we fabricated a conductive copper ion-reinforced sodium alginate (SA) aerogel based free-standing Si anode (Si@CNTs/Alg-Cu-II) containing silicon nanoparticles, sodium alginate aerogel, carbon nanotubes and Cu nanoparticles, via a simple, low-cost and sustainable process (under 1 × 10−1 Pa, 1 °C/min to 200 °C holding for 1 h). In the irregular lamellar porous aerogel, silicon particles with good dispersion are bound by macromolecular chains of SA via dynamic hydrogen bonds and subsequently restrained in the porous aerogel to release volume stress. The in situ generated Cu particles and well-dispersed carbon nanotubes (CNTs) construct the conductive network around Si particles to improve the electrical conductivity of the electrode. This unique structure delivers a capacity of 835.6 mAh/g after 100 cycles at 0.1 A/g based on the total mass of Si@CNTs/Alg-Cu-II composite (Si content of 25.62%). Moreover, it also shows outstanding stability under high current density (a capacity retention of 84.1% after 100 cycles at 0.5 A/g). The sustainable preparation method and excellent electrochemical performance of Si@CNTs/Alg-Cu-II provide a new strategy to develop high-performance free-standing Si-based anodes for LIBs.

CNTs-improved electromagnetic wave absorption performance of Sr-doped Fe3O4/CNTs nanocomposites and physical mechanism

Electromagnetic wave pollution is a serious environmental problem, and it is urgent to develop high-efficiency electromagnetic wave absorption (EMA) materials. In this paper, carbon nanotubes (CNTs) were combined with Sr-doped Fe3O4 nanoparticles to form Sr-doped Fe3O4/CNTs nanocomposites with by hydrothermal method. After the characterization of microstructure and magnetic properties, EMA properties of Sr-doped Fe3O4/CNTs nanocomposites are investigated in detail. The well-dispersed CNTs lead to the uneven average grain size of Sr-doped Fe3O4 nanoparticles and a little decrease of saturation magnetization. While CNTs greatly improve EMA performance, and SFC1 sample exhibits the minimum reflection loss value of −65.64 dB at 6.32 GHz with the thickness of 3 mm. CNTs reduces the natural resonance of magnetic loss while increasing the permittivity, conductivity, and heterogeneous interfaces. As the result, Sr-doped Fe3O4/CNTs nanocomposites exhibit not only better impedance matching but also higher electric dipole polarization relaxation loss, interfacial relaxation loss, conductivity loss, and eddy current loss. In this way, the excellent EMA performance is attributed to the good impedance matching, intense dielectric loss and enhanced eddy current loss for Sr-doped Fe3O4/CNTs nanocomposites.

Carbon nanotube enhanced selective micro filtration of butanol

In this study, we present the development of a carbon nanotube (CNT), immobilized membrane (CNIM) via a phase inversion process for dewatering butanol via microfiltration. The CNTs enhanced membrane hydrophobicity and butanol permeation via adsorption on the CNTs surface leading to relatively high levels of preconcentration, which was not possible using a plain PTFE membrane. The CNIM exhibited a water contact angle of 136 ± 2°, indicating high hydrophobicity. The contact angle decreased with an increase in butanol concentration due to the strong interaction of the CNTs with the latter. The water-butanol mixtures behaved differently at different concentration zones namely water in butanol, WIB (over 80 percent butanol), butanol in water, BIW (below 30 percent butanol), and butanol-water colloidal mixtures, BWCM (30 to 70 percent butanol). At low or high concentrations of butanol, the butanol was strongly hydrogen bonded with the water, and the separation efficiency was relatively lower, between 6.50 and 15.54 % in the WIB and 1.00 to 3.05 % in the BIW regions. In the BWCM regions, water butanol formed colloidal mixtures the separation efficiency was significantly higher. At a feed butanol concentration of 40 %, the water separation reached as high as 43.40 %, with a flux of 118.08 kg/(m2h). The high separation efficiency was attributed to the influence of well-dispersed CNTs on the CNIM which provided sites for the agglomeration of nano water droplets into larger ones that could be removed more easily, as well as the high partition coefficient of the butanol on the CNIM surface.

Insight into the carbon nanotube agglomeration deteriorated fire safety of epoxy

Carbon nanotube (CNT)/epoxy composite is a star lightweight structure material. However, the reason why well-dispersed CNTs retard the combustion of epoxy while CNT agglomerations always accelerate it instead seems still confusing, which severely limits the further understanding and design of the high-performance CNT/epoxy composite. Herein, with CNT agglomerations inside, 4coCNT/epoxy composite and 2coCNT0.5/epoxy composite were prepared to reveal the truth of the dramatically worsened flame retarding performances compared with their expected values. The void-rich CNT agglomerations were proved to be qualified candlewick-like fillers after directly observing the formations of micron-diameter fiber-like agglomerations by scanning electron microscope (SEM) and X-ray computed tomography (XCT); verifying the ability of CNT agglomerations to allow the epoxy melt to wet, spread, and flow on their surface. The thermogravimetric analysis (TG) and the limited oxygen index (LOI) results suggested that fire is necessary for the CNT agglomeration to worsen the thermostability of composites. With the presence of the liquid-phase combustible epoxy melt in the fire captured by a high-definition camera, all the requirements to induce the candlewick effect were satisfied. Ruling out a popular explanation that the agglomerated CNTs promote polymers' inflammability by cracking chars created during the combustion, a similar but distinct candlewick effect was then proposed and specially defined as “nano-candlewick effect” in the present study. The nano-candlewick effect defeated the flame-retarding free radical scavenging effect of the dangling bonds from coCNT and coCNT0.5, and further worsened the flame retardancy of the epoxy matrix. The detailed working mechanism of the nano-candlewick effect was described. The mechanism is supposed to be appropriate for polymer nanocomposites with candlewick-like fillers inside, and account for the dramatically accelerated combustion.

Improvement of the thermal stability of silicone-based aerogels without deteriorating their flexibility via the incorporation of well-dispersed carbon nanotubes

Improvement of the thermal stability of silicone-based aerogels without deteriorating their flexibility via the incorporation of well-dispersed carbon nanotubes

Improved electrochemical performance using well-dispersed carbon nanotubes as conductive additive in the Ni-rich positive electrode of lithium-ion batteries

Carbon nanotubes (CNTs) are being used as a conductive material to achieve fast charging/discharging properties in high current density LIB systems. However, it is difficult to form a well-distributed electron transfer network within the electrode using CNTs due to their high aggregational properties. In this paper, we propose a strategy to fabricate the positive electrode with well-dispersed CNTs, controlling the solid content and sonication process of the slurry using LiNi0.8Co0.1Mn0.1O2 as the cathode materials. The CNTs are typically not well-mixed within the active material composite and aggregation occurs on the electrode surface in low solid content of under 50 wt%. When the solids content is as high as 70 %, CNTs are more evenly distributed in the electrode as bundled particles, however, there was no performance improvement using the ultra-sonication process. The CNTs at a mass ratio of CNTs at 4 wt% are well distributed in the electrode in 60 wt% of solid content, resulting in improved capacity retentions of 99.1 % after 100 cycles at a current density of 1C. When the electrochemical performance with CNTs was compared with Super P according to 1,2,3 and 4 wt% at a solid content of 60 %, the electrode using CNTs has a generally improved electrochemical performance due to the stable H1-M phase transition and stable average voltage during charging/discharging. Additionally, the excellent cycle ability at 5C with CNTs (92.8 % of capacity retention after 100 cycles) is helped by the fact that little polarization was observed compared with the Super P cells.

Analysis of Electrochemical Performance with Dispersion Degree of CNTs in Electrode According to Ultrasonication Process and Slurry Viscosity for Lithium-Ion Battery.

Lithium-ion batteries (LIBs) continue to dominate the battery market with their efficient energy storage abilities and their ongoing development. However, at high charge/discharge C-rates their electrochemical performance decreases significantly. To improve the power density properties of LIBs, it is important to form a uniform electron transfer network in the cathode electrode via the addition of conductive additives. Carbon nanotubes (CNTs) with high crystallinity, high electrical conductivity, and high aspect ratio properties have gathered significant interest as cathode electrode conductive additives. However, due to the high aggregational properties of CNTs, it is difficult to form a uniform network for electron transfer within the electrode. In this study, to help fabricate electrodes with well-dispersed CNTs, various electrodes were prepared by controlling (i) the mixing order of the conductive material, binder, and active material, and (ii) the sonication process of the CNTs/NMP solution before the electrode slurry preparation. When the binder was mixed with a well sonicated CNTs/NMP solution, the CNTs uniformly adsorbed to the then added cathode material of LiNi0.6Co0.2Mn0.2O2 and were well-dispersed to form a flowing uniform network. This electrode fabrication process achieved > 98.74% capacity retention after 50 cycles at 5C via suppressed polarization at high current densities and a more reversible H1-M phase transition of the active material. Our study presents a novel design benchmark for the fabricating of electrodes applying well-dispersed CNTs, which can facilitate the application of LIBs in high current density applications.

Investigation of the interphase structure in polyamide 6–matrix, multi-scale composites

In this study, we investigated the dispersion of carbon nanotubes and the interphases formed around them in nanocomposites with a polyamide 6 matrix (with carbon nanotube reinforcement) and hybrid composites with the same matrix, reinforced with carbon nanotubes and carbon fibers. Small-angle neutron scattering (SANS) experiments showed that carbon fibers effectively increased the dispersion of the carbon nanotubes. The average size of the carbon nanotube aggregates were significantly smaller, but the reinforcement–matrix interface area was larger in the hybrid composites than in the nanocomposites. Nanotube dispersion had a significant effect on the crystalline structure; the X-ray diffraction patterns showed that in the hybrid composites, the crystallites grew epitaxially on the surface of the well-dispersed carbon nanotubes, which resulted in decreased average crystallite size. In the hybrid composites, the smaller crystallites inferred a larger rigid amorphous fraction in the matrix. The larger interphase fraction in the hybrid composites also led to better mechanical performance.

Tough, conductive hydrogels with double-network based on hydrophilic polymer assistant well-dispersed carbon nanotube for innovative force sensor

Tough, conductive hydrogels with double-network based on hydrophilic polymer assistant well-dispersed carbon nanotube for innovative force sensor

The critical incorporation concentration (CIC) of dispersed carbon nanotubes for tailoring multifunctional properties of ultra-high performance concrete (UHPC)

This study aims to elucidate the effect of carbon nanotube (CNT) concentrations on the mechanical, electrical, shrinkage, and thermal properties of ultra-high performance concrete (UHPC). The stable dispersion of CNTs was achieved using well-dispersed CNT suspension and confirmed by consistent decrease in electrical resistivity. The autogenous shrinkage was effectively reduced by over 30% by incorporating around 0.5 wt% CNT content. While thermal conductivity was gradually increased with increasing CNT dosage, the volumetric heat capacity was minimized, and the thermal diffusivity was maximized at the percolation threshold. The addition of CNTs positively affects engineering properties; however, above 0.5 wt% CNT content, compressive strength, elastic modulus, and thermal diffusivity were deteriorated mainly due to higher porosity from reduced fluidity. From these results, the single value of the critical incorporation concentration of CNTs could be proposed as 0.5 wt% for tailoring the multifunctional properties of CNT/UHPC composites.

Enhanced electrical conductivity of anticorrosive coatings by functionalized carbon nanotubes: effect of hydrogen bonding

Carbon nanotubes and nanofibers (CNFs) are well-known nano additives to produce coating materials with high electrical and thermal conductivity and corrosion resistance. In this paper, coating materials incorporating hydrogen bonding offered significantly lower electrical resistance. The hydrogen bonding formed between functionalized carbon nanotubes and ethanol helped create a well-dispersed carbon nanotube network as the electron pathways. Electrical resistivity as low as 6.8 Ω cm has been achieved by adding 4.5 wt% functionalized multiwalled carbon nanotubes (MWNT-OH) to 75%polyurethane/25%ethanol. Moreover, the thermal conductivity of polyurethane was improved by 332% with 10 wt% addition of CNF. Electrochemical methods were used to evaluate the anti-corrosion properties of the fabricated coating materials. 75%polyurethane/25%ethanol with the addition of 3.0 wt% of MWNT-OH showed an excellent corrosion rate of 5.105 × 10–3 mm year−1, with a protection efficiency of 99.5% against corrosive environments. The adhesion properties of the coating materials were measured following ASTM standard test methods. 75%polyurethane/25%ethanol with 3.0 wt% of MWNT-OH belonged to class 5 (ASTM D3359), indicating the outstanding adhesion of the coating to the substrate. These nanocoatings with enhanced electrical, thermal, and anti-corrosion properties consist of a choice of traditional coating materials, such as polyurethane, yielding coating durability with the ability to tailor the electrical and thermal properties to fit the desired application.

A solution-processable and highly flexible conductor of a fluoroelastomer FKM and carbon nanotubes with tuned electrical conductivity and mechanical performance.

The use of fluoroelastomer nanocomposites for flexible electronics is increasing due to their high deformability and recoverability. Often, a high amount of conductive nanofillers and crosslinking agents is required to improve their mechanical performance, which unfavorably affects the electrical percolation threshold and conductivity due to dispersion issues. Herein, we developed a unique solution mixing (SM) technique by a fine-tuned formulation to obtain well-dispersed carbon nanotubes (CNTs) in fluoroelastomer FKM for both low and high CNT concentrations (0.2 phr and 3 phr). Effective nano-network formation was confirmed by transmission electron microscopy (TEM) and oscillatory shear rheological tests. Compared to the melt mixing (MM) process, the stretchability of neat FKM improves to 503% in the SM process versus 430% in the MM process. The electrical conductivity of the SM samples percolates at significantly lower filler concentrations (i.e., 0.35 phr in SM vs. 0.45 phr in MM) with a maximum value of 7 × 10-1 S cm-1 for 3 phr. Overall, the 2 phr CNT/FKM nanocomposite fabricated by SM exceeds those of carbon-based FKM conductors reported in the literature. The enhanced electrical and mechanical properties include an electrical conductivity of 3 × 10-1 S cm-1, a strain-to-failure of 300%, and a tensile strength at break of 12 MPa. This process is a promising approach for fabricating fluoroelastomer nanocomposites of a mechanically robust and stable stretchable conductor for various wearable electronic devices.

Improved Electrochemical Performance Using Well-Dispersed Carbon Nanotubes as Conductive Additive in the Ni-Rich Positive Electrode of Lithium-Ion Batteries

Improved Electrochemical Performance Using Well-Dispersed Carbon Nanotubes as Conductive Additive in the Ni-Rich Positive Electrode of Lithium-Ion Batteries

Electrical resistivity stability of CNT/cement composites after further hydration: A simple evaluation with an accelerated method

A series of simple, short-term experiments were conducted, utilizing an accelerated testing method, to investigate the long-term reliability of the electrical properties of carbon nanotube (CNT)/cement composites after further cement hydration and the corresponding alkali attack on CNTs. The CNTs were exposed to an alkali solution at high temperatures, their chemical structures were evaluated using X-ray photoelectron spectroscopy, and their electrical properties were evaluated via cyclic voltammetry. The hardened CNT/cement composite specimens were cured in high-temperature water and their electrical resistivities were measured. The non-evaporable composite water content was measured to evaluate the increase in hydration degree via high-temperature water curing. The resistance of the CNT networks scarcely changed, even under the strong alkali conditions of the pore solution; the electrical resistivity of the cement composites with well-dispersed CNT networks remained unchanged. The findings indicate that the CNT/cement composites exhibit acceptable electrical stability for practical sensors.

Rheological, electrical, and dynamic thermomechanical properties: Comparison between multiwall and double-wall carbon nanotubes in polylactide and polyamide 11

In this study, multiwall carbon nanotubes (MWCNTs) and double-wall carbon nanotubes (DWCNTs) have been dispersed in polylactide (PLA) and polyamide 11 (PA11) using an internal mixer. Rheological characterization confirmed the formation of carbon nanotube (CNT) networks in PLA and PA11 attributed to well-dispersed CNTs in the respective matrices. A lower rheological percolation threshold of PLA/MWCNT nanocomposites (less than 0.5 wt. %) compared to PA11/MWCNT nanocomposites (about 2 wt. %) confirmed the greater affinity of CNTs for PLA. The threshold for DWCNTs was below 0.5 wt. % in PLA and between 0.5 and 1 wt. % in PA11. PLA-based nanocomposites also showed higher electrical conductivity values compared to PA11-based nanocomposites. Nanocomposites containing DWCNTs exhibited higher electrical conductivities compared to those containing MWCNTs due to the higher aspect ratio of DWCNTs. Dynamic mechanical thermal analysis showed enhanced storage modulus values and reduced damping behavior with increasing content of CNTs for both polymers.

PDMS Sponges with Embedded Carbon Nanotubes as Piezoresistive Sensors for Human Motion Detection.

Porous piezoresistive sensors offer promising flexible sensing functionality, such as human joint motion detection and gesture identification. Herein, a facile fabrication method is developed using a microwave-based rapid porogen removal technique for the manufacturing of porous nanocomposite sponges consisting of polydimethylsiloxane (PDMS) and well-dispersed carbon nanotubes (CNTs). The porogen amounts and CNT loadings are varied to tailor the porosity and electrical properties of the porous sensors. The sponges are characterized by a scanning electron microscope (SEM) to compare their microstructures, validate the high-quality CNT dispersion, and confirm the successful nanofiller embedding within the elastomeric matrix. Sponges with a 3 wt% CNT loading demonstrate the highest piezoresistive sensitivity. Experimental characterization shows that the sponges with low porosity have long durability and minimal strain rate dependence. Additionally, the developed sponges with 3 wt% CNTs are employed for the human motion detection using piezoresistive method. One experiment includes fingertip compression measurements on a prosthetic hand. Moreover, the sensors are attached to the chest, elbow, and knee of a user to detect breathing, running, walking, joint bending, and throwing motions.

The Influence of Reaction Time on Non-Covalent Functionalisation of P3HT/MWCNT Nanocomposites.

Non-covalent functionalisation of the carbon nanotube (CNT) sidewall through polymer wrapping is the key strategy for improving well-dispersed CNTs without persistent alteration of their electronic properties. In this work, the effect of reaction time on regioregular poly (3-hexylthiophene-2,5-diyl) (P3HT)-wrapped hydroxylated multi-walled CNT (MWCNT-OH) nanocomposites was investigated. Five different reaction times (24, 48, 72, 96, and 120 h) were conducted at room temperature in order to clearly determine the factors that influenced the quality of wrapped MWCNT-OH. Morphological analysis using Field Emission Scanning Electron Microscopic (FESEM) and High-Resolution Transmission Electron Microscope (HRTEM) analysis showed that P3HT successfully wrapped the MWCNT-OH sidewall, evidenced by the changes in the mean diameter size of the nanocomposites. Results obtained from Raman spectroscopy, X-ray Photoelectron Spectroscopy (XPS) as well as Thermogravimetric Analysis (TGA) showed a significant effect of the wrapped polymer on the CNT sidewall as the reaction time increased. Overall, the method used during the preparation of P3HT-wrapped MWCNT-OH and the presented results significantly provided a bottom-up approach to determine the effect of different reaction times on polymer wrapping to further expand this material for novel applications, especially chemical sensors.

Role of Well-Dispersed Carbon Nanotubes and Limited Matrix Degradation on Tribological Properties of Flame-Sprayed PEEK Nanocomposite Coatings

Abstract High-performance carbon nanotubes reinforced polyether ether ketone (CNTs/PEEK) nanocomposites display an excellent combination of mechanical, thermal, and tribological properties. It is a challenge to deposit high-performance CNTs/PEEK nanocomposite coatings via the coating techniques based on solution or melting processes due to low solubility and high melting point of PEEK for tribological applications. In this work, the CNTs/PEEK nanocomposite coatings with CNTs contents of 0.1, 0.5, 1.0, and 2.0 wt% were prepared by flame spraying of mixed PEEK and CNTs powders using mechanical blending (MB) and ultrasound dispersion (UD) methods. The flame-sprayed CNTs/PEEK nanocomposite coatings using UD powders preserved good CNTs dispersion, low porosity, and surface roughness, adhesive coating–substrate interfaces. The thermal degradation of PEEK ascribed to overheating of in-flight particles and flame-rescanning coatings was limited by good CNTs dispersion in flame-sprayed CNTs/PEEK nanocomposite coatings with an increase of CNT contents. The good dispersion of CNTs aided in initiating crystallization and confined crystalline growth resulting in high crystallinity degree and small crystallite size of PEEK matrix in the flame-sprayed CNTs/PEEK nanocomposite coatings. The uniform nanocomposite coatings with well-dispersed CNTs and few PEEK degradation in optimum content of 1.0 wt% preserved enhanced microhardness and superiorly tribological properties. The well-dispersed CNTs bonding with PEEK matrix enhanced the mechanical strength to restrict the generation of fatigue cracks from defects of voids, which promoted self-lubrication and wear resistance of flame-sprayed CNTs/PEEK nanocomposite coatings.

Improved thermal stability of silicone rubber nanocomposites with low filler content, achieved by well-dispersed carbon nanotubes

Improvement of the properties of polymer materials can extend the applicable fields of their usage. In this study, we present that the dispersibility of carbon nanotubes (CNTs) plays a critical role in the thermal stability of CNT/silicone rubber nanocomposites. Appropriate dispersion, which can be confirmed by a Raman mapping technique, can increase the temperatures at 5% weight loss (Td,5%) of the CNT/silicone rubber nanocomposites. Moreover, thermal aging tests have revealed that CNT/silicone rubber nanocomposites fabricated by appropriate dispersion process can retain rubbery elasticity after 7 days at 280 °C, at which condition pristine silicone rubber become embrittled only after one day. Furthermore, we found that these improvements in thermal stability of CNT/silicone rubber nanocomposites can be achieved by loading only of 0.05 wt% CNT in optimized conditions. Our findings indicate that appropriate dispersion can extract the potential of CNTs, and can impart objective properties effectively to their nanocomposites.