Pristine Carbon Nanotube Film Research Articles

(Digital Presentation) Preparation and Characterization of PMMA-SWCNT Nanocomposites

Carbon nanotubes (CNTs) exhibit unique properties such as high tensile strength, excellent electrical conductivity, and resistance to corrosion. Unfortunately, macroscopic objects from these nanostructures do not perform equally well because the individual nanotubes do not transfer electrical charge, phonons, or stress between them sufficiently well. One possible solution to improve the properties of macroscopic ensembles from nanocarbon is to manufacture the composites with other materials like polymers, ceramics, or metals. This connection is usually beneficial. However, the properties depend strongly on the integration degree of the two compounds. For example, nanocomposites with polymers have improved mechanical (Poly(methyl methacrylate), PMMA) or electrical (in the cause of conductive polymers) properties. Many ways lead to PMMA-CNTs, but the most popular are coating (dip-coating, spin-coating, spray-coating) and dispersion methods.One of the potential applications of these composites is as a membrane for the purification of wastewater from organic residues. Unfortunately, industrial growth in the last century has caused a reduction in the availability of pure water, so the abovementioned application of CNTs would be beneficial. However, the main problem with pristine carbon nanotube films is their structural integrity. The addition of polymer molecules could overcome this problem and lead to a new effective method of removing impurities.The commercial single-walled carbon nanotubes (TuballTM) were used to create nanocomposites with PMMA using either dip-coating or dispersion method. Scanning Electron Microscopy (SEM), Raman spectroscopy, Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy, and mechanical testing were used to analyze composites. The nanocomposites were used to remove aromatic organic compounds dissolved in water. For model substances methyl orange, methylene blue, and fluorescein were chosen. UV-VIS spectroscopy was used to gauge the concentration of organic compounds before/after the filtration of the aqueous solution dissolved therein. The best results were for SWCNTs and PMMA-SWCNTs membranes as they removed more than 99% of chosen water impurities.

Densification of single-walled carbon nanotube films: Mesoscopic distinct element method simulations and experimental validation

Nanometer-thin single-walled carbon nanotube (CNT) films collected from the aerosol chemical deposition reactors have gathered attention for their promising applications. Densification of these pristine films provides an important way to manipulate mechanical, electronic, and optical properties. To elucidate the underlying microstructural level restructuring, which is ultimately responsible for the change in properties, we perform large scale vector-based mesoscopic distinct element method simulations in conjunction with electron microscopy and spectroscopic ellipsometry characterization of pristine and densified films by drop-cast volatile liquid processing. Matching with the microscopy observations, pristine CNT films with a finite thickness are modeled as self-assembled CNT networks comprising entangled dendritic bundles with branches extending down to individual CNTs. Simulations of these films under uniaxial compression uncover a soft deformation regime extending up to an ∼75% strain. When removing the loads, the pre-compressed samples evolve into homogeneously densified films with thickness values depending on both the pre-compression level and the sample microstructure. The significant reduction in thickness is attributed to the underlying structural changes occurring at the 100 nm scale, including the zipping of the thinnest dendritic branches.

Ultrathin Densified Carbon Nanotube Film with "Metal-like" Conductivity, Superior Mechanical Strength, and Ultrahigh Electromagnetic Interference Shielding Effectiveness.

Flexible and lightweight high-performance electromagnetic interference shielding materials with minimal thickness, excellent mechanical properties, and outstanding reliability are highly desired in the field of fifth-generation (5G) communication, yet remain extremely challenging to manufacture. Herein, we prepared an ultrathin densified carbon nanotube (CNT) film with superior mechanical properties and ultrahigh shielding effectiveness. Upon complete removal of impurities in pristine CNT film, charge separation in individual CNTs induced by polar molecules leads to strong CNT-CNT attraction and film densification, which significantly improve the electrical conductivity, shielding performance, and mechanical strength. The tensile strength is up to 822 ± 21 MPa, meanwhile the electrical conductivity is as high as 902,712 S/m, and the density is only 1.39 g cm-3. Notably, the shielding effectiveness is over 51 dB with a thickness of merely 1.85 μm in the broad frequency range of 4-18 GHz, and it reaches to ∼82 dB at 6.36 μm and ∼101 dB at 14.7 μm, respectively. Further, such CNT film exhibits excellent reliability after an extended period in strong acid/alkali, high temperature, and high humidity. It demonstrates the best overall performance among representative shielding materials by far, representing a critical breakthrough in the preparation of shielding film toward applications in wearable electronics and 5G communication.

Simultaneous Improvement on Strength, Modulus, and Elongation of Carbon Nanotube Films Functionalized by Hyperbranched Polymers.

Carbon nanotube (CNT) buckypapers, or films, have the potential for wide applications because of their unique properties. Neat buckypapers or pristine CNT (PCNT) films have relatively large elongation but low strength and low modulus due to the weak interaction between CNTs. Chemical modifications of PCNT films can significantly strengthen the interaction between CNTs, resulting in high strength and high modulus but usually accompanied by low elongation. Here, we report the functionalization of pristine CNT films by thiol-ended hyperbranched polymers (THBP-n) via a thiol-ene click reaction that can introduce simultaneous improvements on the strength, modulus, and elongation to the PCNT film by 689, 812, and 32.4%, respectively. The high thiol content of THBP-n enables the formation of a network with a high degree of cross-linking between carbon nanotubes, which provides high-efficiency load transfer that increases the tensile strength and modulus of the resulting films and at the same time a compressible hyperbranched structure that allows for deformation and slip between CNTs and consequently improved elongation. The main factors affecting the mechanical performance of the functionalized CNT film are also investigated.

Fabrication of thermally robust carbon nanotube (CNT)/SiO2 composite films and their high-temperature mechanical properties

Carbon nanotube (CNT) films have shown great promise for a wide range of applications such as high-performance composites, energy devices, and environmental protection. However, the mechanical degradation of CNT films under high temperatures caused by their inherent weak oxidation resistance significantly limits their application in high-temperature environments. This paper presents a method for improving the mechanical properties and thermal stability of CNT films using SiO2-coating modification. The SiO2 precursor was first uniformly infiltrated into a CNT film via a vacuum-assisted filtration method. The SiO2 precursor was then decomposed under a controlled temperature to form an amorphous SiO2 layer wrapped on the CNTs. This treatment remarkably enhanced the mechanical performance of the CNT film, with a tensile strength of 180.9 MPa, which was 200% higher than that of the pristine CNT film. The SiO2-modified CNT film also exhibited excellent thermal stability at 500 °C, making it possible to expand its usage in high-temperature environments. The mechanism of the enhanced mechanical properties and thermal stability of the SiO2/CNT film is also discussed.

Observations of copper deposition on functionalized carbon nanotube films

This research details the spontaneous electroless and electrodeposition of copper onto carbon nanotube (CNT) film from a copper sulfate electrolyte. Inhomogeneous electrodeposition was found to occur on pristine CNT film due to differences in available active nucleation sites and the hydrophobic nature of the film. In order to improve the electrochemical response of CNT films, oxidative pre-treatments such as heat treatment and anodization were investigated. These treatments were shown to increase the amount of oxygen containing defects at the surface of CNT film material. Incorporation of functional groups were shown to enhance the wetting of the aqueous electrolyte and created a highly active surface suitable for homogenous electrodeposit. Cathodic polarization curves showed that the presence of functional groups decreased the required level of polarization for copper deposition. Nevertheless, after a certain level of functionalization the polarization starts to decrease due to increased resistivity of the CNT film. Oxygen grafted CNT films were also shown to exhibit enhanced adsorption and reduction of copper without applied voltage due to redox replacement reactions, which were observed to increase with enhanced levels of functionalization.

The loading-rate dependent tensile behavior of CNT film and its bismaleimide composite film

Carbon nanotube (CNT) macroscopic assembly, as a promising candidate for the protective and anti-collision materials, has attracted lots of researchers to explore its mechanical behavior under different loading rates. In this paper, the loading-rate dependent mechanical behavior of CNT film and its composite with bismaleimide (BMI) matrix is investigated. The pristine CNT film shows decreased tensile strength by 33.8% when the loading rate increases from 0.05mm/min to 40mm/min. An obvious necking extending phenomenon is observed in the CNT film during the tensile test under lower tensile rates, e.g. 0.05mm/min and 0.5mm/min. However, the random composite film and the oriented composite film both display increased tensile strength, by 58.2% and 35.7% respectively, with the increasing loading rate from 0.05mm/min to 40mm/min. The different loading-rate dependence of tensile behavior is ascribed to the different tensile-induced motions of CNTs and CNT bundles in composite film. Moreover, strain rate sensitivity coefficients of different film are calculated according to a simplified Johnson-Cook model. The results suggest that the pristine CNT film with the strain rate sensitivity coefficient of −0.0941 has a high loading-rate sensitivity, meanwhile polymer infiltration and oriented alignment can weaken the loading-rate sensitivity of CNT film.

Electromagnetic characteristics of carbon nanotube film materials

Carbon nanotube (CNT) possesses remarkable electrical conductivity, which shows great potential for the application as electromagnetic shielding material. This paper aims to characterize the electromagnetic parameters of a high CNT loading film by using waveguide method. The effects of layer number of CNT laminate, CNT alignment and resin impregnation on the electromagnetic characteristics were analyzed. It is shown that CNT film exhibits anisotropic electromagnetic characteristic. Pristine CNT film shows higher real part of complex permittivity, conductivity and shielding effectiveness when the polarized direction of incident wave is perpendicular to the winding direction of CNT film. For the CNT film laminates, complex permittivity increases with increasing layer number, and correspondingly, shielding effectiveness decreases. The five-layer CNT film shows extraordinary shielding performance with shielding effectiveness ranging from 67dB to 78dB in X-band. Stretching process induces the alignment of CNTs. When aligned direction of CNTs is parallel to the electric field, CNT film shows negative permittivity and higher conductivity. Moreover, resin impregnation into CNT film leads to the decrease of conductivity and shielding effectiveness. This research will contribute to the structural design for the application of CNT film as electromagnetic shielding materials.

Thermo-responsive surface wettability on a pristine carbon nanotube film

A superhydrophobic carbon nanotube (CNT) film is fabricated by a simple spray-coating method without any chemical modification. The superhydrophobic surface changes after heating to a state of superhydrophilic wettability, and such transition may be attributed to the change of electronic structures of CNTs since the surface structure and composition after treated remain the same as the pristine CNTs. The initial wettability state is reestablished within 24 h of storage in air, and the time can be shortened to only 1 min when the heated CNT film was stored in deionized water.

Piezoresistive effect in carbon nanotube films

The piezoresistive effect of the pristine carbon nanotube (CNT) films has been studied. Carbon nanotubes were synthesized by hot filament chemical vapor deposition. The piezoresistive effect in the pristine CNT films was studied by a three-point bending test. The gauge factor for the pristine CNT films under 500 microstrains was found to be at least 65 at room temperature, and increased with temperature, exceeding that of polycrystalline silicon (30) at 35°C. The origin of the piezoresistivity in CNT films may be ascribed to a pressure-induced change in the band gap and the defects.