Establishment, morphology and properties of carbon nanotube networks in polymer melts

This paper explores the characterization of dielectric and conductive properties of carbon nanotube (CNT) networks. This is carried out by building planar transmission lines where conventional metallic traces are replaced by CNT networks. The proposed transmission lines with CNT networks are presented. Experimental realization and repeated two-port microwave measurements of proposed transmission lines enable the accurate extractions of their fundamental parameters showing percolation effects due to presence of CNT networks. The frequency-dependent phase velocity characteristics show a dramatic reduction compared to the speed of light in vacuum. The large magnitude of extracted complex permittivity for CNT networks also exhibits its percolation performance. The effects of CNTs' bulk density on measured and calculated parameters are explained. The results presented in this paper demonstrate the feasibility and the potential of building transmission lines and radio-frequency (RF) circuits elements using CNT networks.

Aggregation of nanoparticles and their effect on mechanical properties of carbon nanotube networks

Carbon nanotube (CNT) macrostructures like anisotropic CNT arrays and isotropic CNT networks have many unique mechanical properties. Among the various properties of CNT networks, their collective responses to compressive deformation are studied here. A rheological model is found to account for the mechanical properties of CNT networks. The computational results show that the compressive responses of CNT networks include the mechanical action of interconnected springs and dry friction elements. The availability of the model is validated by comparing the computed results to the measured data of different density CNT sponges. The good agreement between the computed and measured results suggests that the compressive responses of CNT segments and the sliding friction between CNTs are the major factors contributing to the compressive responses of CNT networks. The effectiveness of the model in describing the CNT networks also indicates that their collective responses are similar to that of the rheological model during the compression cycle.

Tailoring optical and electrical properties of carbon nanotube networks for photovoltaic applications

This paper explores building planar transmission lines using carbon nanotube (CNT) networks. Transmission lines with carbon nanotube networks replacing the conventional metallic traces are presented. The experimental realization and the repeated two-port microwave measurements of the proposed transmission lines enable accurate extractions of the fundamental parameters showing percolation effects in CNT networks. The frequency-dependent phase velocity characteristics show a dramatic reduction compared to the speed of light in vacuum. The large magnitude of extracted complex permittivity for CNT networks also exhibits its percolation performance. The effects of CNTs' bulk density on measured and calculated parameters is explained.

Enhanced mechanical properties of carbon nanotube networks by mobile and discrete binders

In this paper, we explore building planar transmission line from carbon nanotube (CNT) networks. We are successful in fabricating the transmission line and verifying the feasibility of potential planar transmission lines where carbon nanotube networks replace the metallic lines. The experimental realization and the two-port microwave measurements enabled us to extract accurately the fundamental parameters of the proposed transmission line. The frequency-dependent phase velocity characteristics show clearly its dramatic reduction compared to speed of light in vacuum. The complex permittivity of CNT networks is also reported in our work.

The network of entangled multiwall carbon nanotubes and the composite consisting of a polystyrene filter-supported nanotube are introduced as conductors whose conductivity is sensitive to compressive stress both in the course of monotonic stress growth and when loading/unloading cycles are imposed. The testing has shown as much as a 100% network conductivity increase at the maximum applied stress. It indicates the favorable properties of the multiwall carbon nanotube network for its use as a stress-electric signal transducer. To model the conductivity–stress dependence, it is hypothesized that compression increases local contact forces between the nanotubes, which in turn leads to a decrease in the contact resistance between them. The lack of detailed knowledge of the mechanism as well as an unclear shift from individual contacts to the whole network conductance behavior is circumvented with a statistical approach. In this respect, the conductivity/compression data were fitted well using the Weibull distribution for the description of the nanotube contact resistance distribution.

We report a theoretical investigation of the mechanical properties of idealized networks formed by single-walled carbon nanotubes showing crossbar and hexagonal architectures. The study was performed by using molecular mechanics calculations and impact dynamics simulations based on bond-order empirical potential. The studied networks were predicted to have elasticity modulus of $\ensuremath{\sim}10--100\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ and bulk modulus of $\ensuremath{\sim}10\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$. The results show a transition from high to moderate flexibility during the deformation stages. This behavior was associated with the existence of two deformation mechanisms presented by the network related to the nanotube stretching and junction bending processes.

Influence of shear deformation on the electrical and rheological properties of combined filler networks in polymer melts: Carbon nanotubes and carbon black in polycarbonate

A latex-based concept for making carbon nanotube/polymer nanocomposites

Carbon nanotubes (CNTs), since the discovery by Iijima, have attracted tremendous interests in scientific research mainly due to their exceptional structure and physical properties. The high aspect ratio, light weight, extraordinary stiffness, and strength make CNTs a potentially very functional material to be used in polymer nanocomposites application. Carbon nanotubes are single or multilayered coaxial tubes of six-membered ring networks composed of carbon. It is an allotrope of carbon and is sometimes classified as a type of fullerene. Carbon nanotubes are expected to be applied to materials that normally do not conduct heat or electricity, such as resin, rubber, ink, and paint. In addition, it is expected to be applied to the electronics field because of its conductivity and thermal conductivity even in small quantities and high strength when made into long lengths. One of the problems of CNTs is the tendency of CNTs to aggregate with each other due to intermolecular interactions. In the aggregated state, CNTs cannot exhibit their inherently useful characteristics, and therefore, a technology to disperse CNTs at the nano-level is required. Currently, two major methods are being considered for dispersing CNTs: The first is dispersion by chemical modification. By introducing carboxylic acid into strong acid treated CNTs and introducing hydrophilic or hydrophobic substituents here, solubilization in water or organic solvents is possible. However, there is a problem that this destroys the structure of CNTs and thus greatly impairs their original properties.The other method is to physically disperse CNTs. This is a very simple method that uses ultrasonic irradiation to loosen bundled CNTs, but the dispersion is only temporary, and re-agglomeration occurs quickly. Problems have also been reported, such as excessive ultrasonic irradiation destroying the structure of the CNTs. We have succeeded in producing CNTs nano dispersion gels by adding an aromatic compound to agglomerated CNTs and applying agitation and ultrasonic irradiation. The following describes the process of preparing CNTs dispersion gels. After agglomerated CNTs are temporarily dispersed by ultrasonic irradiation, an aromatic compound (dispersant) is added and mixed and agitated. The dispersed CNTs and the aromatic compound are combined by π-π interaction, and the aromatic compound is adsorbed on the CNTs surface. When CNTs molecules adsorbed with aromatic compounds approach each other, the aromatic compounds on the surface form π-π interactions. At this point, the CNTs are in a gel-like state. Since this dispersion gel does not chemically modify the CNTs, it can be prepared without destroying the structure of the CNTs. The CNTs gel proved to be free from aggregation even after the dispersant component was removed, and the network structure was maintained. In addition, this dispersion gel shows high electrical conductivity because the CNTs are dispersed three-dimensionally and the CNTs form three-dimensional conductive paths in the gel.Next, we introduce the preparation of CNT composite resin. CNT composite resin is prepared by adding binder resin to the carbon nanotube dispersion gel prepared earlier, mixing, and stirring, and ultrasonic irradiation. A transparent conductive film is created by forming the prepared CNT composite resin on a glass slide. In recent years, transparent conductive films have been in high demand due to the development of electronics products, and the use of CNTs as the main material is expected to significantly reduce the cost of development, as they are less expensive than Metallic materials such as indium tin oxide and can be stably supplied. The challenge of this research is that the amount of black CNTs added, which imparts conductivity, significantly affects the transparency of the transparent conductive film. Therefore, it is necessary to select aromatic compounds and resin materials that achieve both high conductivity and transparency with low amounts of added CNTs from a molecular chemistry perspective. In our previous research, we focused on the chemical bonding between resin materials and CNTs for the first time and attempted to improve electrical conductivity by using hydrogen bonding for CNTs. In addition, by combining polycarbonate, which exhibits high transparency and impact resistance, with CNT dispersion gel, we attempted to fabricate a transparent conductive film with high durability. As a result, we succeeded in developing a transparent conductive film material with performance applicable to touch panels.In this study, CNTs dispersion gels prepared with aromatic compounds were evaluated using absorbance measurements and Raman spectroscopy. The Raman spectra measurements allowed us to quantitatively evaluate the interaction between SWCNTs and aromatic compounds. The possibility of charge-transfer complex formation was also suggested by the results of absorbance measurements. Figure 1

The present work suggests a simple model for viscosity of polymer carbon nanotubes (CNT) biosensor assuming CNT concentration, CNT dimensions, interphase thickness, and network size. CNT concentration, CNT size, and interphase thickness express the effective filler concentration and the percolation threshold, which determine the fraction of networked CNT in nanocomposite biosensors. The experimental results of viscosity for the prepared samples containing poly(lactic acid) (PLA), poly(ethylene oxide) (PEO), and carbon nanotubes (CNT) are measured to approve the suggested model. Moreover, the developed model presents the roles of all parameters in the viscosity to confirm the predictions. The predictions properly agree with the experimental data of samples demonstrating the predictability of the developed model. Thin and large CNT (high aspect ratio) mainly increase the viscosity, while thick or short CNT produce very low viscosity. A high CNT concentration and thick interphase significantly enhance the viscosity, while a low content of CNT or a thin interphase cause an extremely low viscosity. In addition, the percentage of CNT in the networks directly manipulates the viscosity. POLYM. COMPOS., 40:4135–4141, 2019. © 2019 Society of Plastics Engineers

In this paper, Paul’s model is advanced to forecast the tensile modulus of polymer nanocomposites reinforced by carbon nanotubes (CNT) above percolation onset. The developed model assumes the CNT network density by CNT aspect ratio (α), percolation onset and CNT density (n). The experimental results from several samples containing a filler network confirm the predictability of the advanced model. However, undesirable results are reported for the samples without the filler network. Also, both α and n directly manipulate the nanocomposite’s modulus above percolation onset, because they positively influence the polymer-CNT interfacial area and network size. The reasonable effects of α, n and percolation onset on the predicted moduli of nanocomposites validate the developed Paul model.

Carbon nanofiller networks- a comparative study of networks formed by branched versus linear carbon nanotubes in thermoplastic polyurethane