CNT-polymer Composites Research Articles

Recent Advances in Bioactive Carbon Nanotubes Based on Polymer Composites for Biosensor Applications.

Recent breakthroughs in the field of carbon nanotubes (CNTs) have opened up unprecedented opportunities for the development of specialized bioactive CNT-polymers for a variety of biosensor applications. The incorporation of bioactive materials, including DNA, aptamers and antibodies, into CNTs to produce composites of bioactive CNTs has attracted considerable attention. In addition, polymers are essential for the development of biosensors as they provide biocompatible conditions and are the ideal matrix for the immobilization of proteins. The numerous applications of bioactive compounds combined with the excellent chemical and physical properties of CNTs have led to the development of bioactive CNT-polymer composites. This article provides a comprehensive overview of CNT-polymer composites and new approaches to encapsulate bioactive compounds and polymers in CNTs. Finally, biosensor applications of bioactive CNT-polymer for the detection of glucose, H2O2 and cholesterol were investigated. The surface of CNT-polymer facilitates the immobilization of bioactive molecules such as DNA, enzymes or antibodies, which in turn enables the construction of state-of-the-art, future-oriented biosensors.

One-step photo-induced modification of carbon nanotubesviapolymeric diazonium chemistry

A novel strategy for the preparation of CNT–polymer composites in a one-step photo-induced route was proposed based on polymeric diazonium chemistry, notable for its universality in both aqueous and organic solutions.

Fragmentation and release of pristine and functionalized carbon nanotubes from epoxy-nanocomposites during accelerated weathering.

There is an increasing volume of nano-enabled materials in the market. Once composites containing nano-additives are disposed of, weathering could deteriorate their structures, releasing nanoparticles and risking exposure of humans and aquatic organisms. Composite degradation due to environmental aging continues, including structural deterioration resulting in cracking, fragmentation, and release of microplastics and nano-additives to the environment. This research aims to study the degradation and release of initially embedded nanomaterials (NMs) from composites and their toxicity. The molecular interaction of carbon nanotube (CNT)/polymer composites is critical for modifying the polymer properties. This study investigated the interactions of functional multiwalled carbon nanotube (MWCNT) composites which affect their release during accelerated weathering processes. Different epoxy-MWCNT composites were prepared by filling a polymer with pure MWCNTs and MWCNTs functionalized with acid () and amine () groups. The physical and chemical changes of aged composites were characterized by gravimetric analysis, contact angle measurements, FTIR, SEM, and laser confocal microscopy. A loss of hydrophobicity was observed for composite surfaces long before surface cracks materialized. Released polymer fragments and nanoparticles were analyzed in wash water using TEM, FTIR and Raman spectroscopy. The environmental risks for long-term use of CNT-polymer composites and the influence of fillers on the extent of chemical photodegradation depended on the combination of polymer and fillers. If nanoparticles are released from the matrix, the high surface-to-volume ratio and reactivity of NMs make them highly dynamic in environmental systems. Exposure to these released NMs could negatively affect human health and the environment. This study provides fragmentation and CNT particle release data that could describe how molecular-level interactions between functionalized CNTs and epoxy polymers affect the aging and release of CNTs. A toxicity assessment based on a reactive oxygen species (ROS) formation assay and MTS assay for cell viability and activity of the released polymer and CNT fragments and leachate showed moderate levels of cytotoxicity of released materials as compared to pristine epoxy plates.

Flexible Bonding of Polymer Substrates By Microwave Heating of Carbon Nanotubes

Recently, as research on developing electronic devices for simultaneous implementation of flexibility and conductivity has been continuously conducted, ensuring stable and high reliability of devices in preparation for various mechanical deformation is becoming important. When a physical force such as bending, twisting, or folding is applied, the bonding area between two substrates should ensure stability due to high stress generation. Epoxy resin materials used as standard adhesive agents have brittleness due to the nature of the material, and are weak in terms of flexibility due to increased bonding thickness due to high temperature hardening. In addition, it is difficult to apply as a bonding material in consideration of thermal deformation of the polymer substrate exposed to high temperatures during the process. To improve both flexibility and durability against fatigue deformation, Flexible bonding process is required without adhesive such as epoxy resin with poor brittleness. Surface activation bonding technologies by ion beams and vacuum ultraviolet rays have been developed in previous studies, bonding between plastic substrates by activating thin metal films surface of adhesive layer with ion beam or improving adhesive force by direct-UV radiation on the surface of the polymer substrate. In this study, a flexible bonding process between polymer substrates was developed by heating carbon nanotubes (CNTs) through microwave irradiation. High microwave absorption properties of CNT lead to heat dissipation behavior and light emission characteristics. Heat transfer mechanism of CNT applied to CNT-polymer composites, CNT electrodes fields and has been microwave assisted purification. By utilizing the microwave heating effect, we selected CNT materials for flexible substrates. Multi-walled carbon nanotubes (MWNTs) were coated on a bonded PET polymer substrate and then local heating was performed by microwaves to induce mechanical entanglement between the CNTs and the PET. In the bonding process, the output power of the microwave was adjusted to 600,800 and 1000 Watt, and the bonding strength was evaluated by quantifying the bonding strength was evaluated. For the analysis of the bonding mechanism in the area where mechanical entanglement took place, the CNT-PET bonding interface was analyzed through electron scanning microscope (SEM) measurement, and further analysis was performed for each process condition. In addition, a fracture mechanism analysis that occurred at the junction was performed after the overlapping shear strength test. Acknowledgments This work was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (2020M3H4A3106413, Development of Evaluation Method for Mechanical Deformation of Micro-joints in Micro-LED Module) Figure 1

Modelling the effects of carbon nanotube length non-uniformity and waviness on the electrical behavior of polymer composites

Carbon nanotube (CNT) length non-uniformity and waviness exist inevitably in practical CNT/polymer composites (CPCs) and are two major factors that have significant influences on the composite electrical behavior. However, these two factors have been rarely considered simultaneously in previous modellings. In this study, a numerical model is presented to predict the electrical behavior of CPCs by simultaneously taking into account the two factors besides other ones considered in existing modellings. The length non-uniformity of CNTs is represented by the Weibull distribution and each wavy CNT is modeled by a piecewise sequence of several line segments. Besides, the tunneling distance is reasonably defined to calculate the tunneling resistance between adjacent CNTs. The prediction results reveal that both the CNT length non-uniformity and waviness have significant effects on the electrical behavior of CPCs. It is shown that the percolation threshold evidently decreases with either increasing the CNT length non-uniformity or decreasing the CNT waviness degree. Furthermore, the predictions agree well with existing experimental data, indicating the validity of the present numerical model in predicting the electrical conductivity of CPCs. In particular, it should be emphasized that compared with the previous models without simultaneously considering the effects of these two factors, the present model provides better predictions of the electrical behavior of CPCs.

Multi-functional and integrated actuators made with bio-inspired cobweb carbon nanotube–Polymer composites

Soft actuators have emerged as flexible platforms that can integrate many functional electronic devices to build intelligent electronic systems. The energy supply and wireless signal transmission of electronic systems of the multi-functional actuators are challenging research areas. Here, the idea of the functionalized and hierarchical design is proposed to construct the multi-functional and integrated actuators. Inspired by the structure of cobwebs, multi-functional carbon nanotube (CNT)-polymer composites with network structures are proposed and applied in multi-responsive actuators, supercapacitors, and electromagnetic interference (EMI) shielding devices. Two multi-functional and integrated actuators are highlighted to demonstrate the practical applications. One is a light-driven actuator integrated with an EMI shielding function, which can be used as an intelligent shielding curtain. The other is an electrical-driven actuator integrated with an energy storage function. Especially, the functions of actuation and energy storage can be simultaneously/independently used without interfering with each other. We provide comprehensive research from the material level (CNT-polymer composites) to the device level (actuators, supercapacitors, EMI shielding devices), and then to the system level (multi-functional actuators). We believe that the integration design of the multi-functional actuators will open up new avenues for the development of soft robotics, wireless signal transmission switch, and deformable supercapacitors.

On the electrical conductivity of composites with a polymeric matrix and a non-uniform concentration of carbon nanotubes

We present a multiscale modelling approach to explore the effects of a non-uniform concentration of carbon nanotubes (CNTs) on the electrical conductivity of CNT-polymer composites. Realistic three-dimensional representative volume elements (RVEs) are generated from a two-dimensional CNT concentration map, obtained via microscopy techniques. The RVEs capture the measured probability density function of the CNT concentration and include a length-scale to represent the details of the spatial distribution of the concentration. The homogenized conductivity of the RVEs is computed via multiscale FE analyses for different values of such length-scale, and it is compared to measurements. The modelling strategy is then used to explore the effects of the microstructural features of these materials on their electrical conductivity.

Application of machine learning to predict the multiaxial strain-sensing response of CNT-polymer composites

We present predictive multiscale models of the multiaxial strain-sensing response of conductive CNT-polymer composites. Detailed physically-based finite element (FE) models at the micron scale are used to produce training data for an artificial neural network; the latter is then used, at macroscopic scale, to predict the electro-mechanical response of components of arbitrary shape subject to a non-uniform, multiaxial strain field, allowing savings in computational time of six orders of magnitude. We apply this methodology to explore the application of CNT-polymer composites to the construction of different types of sensors and to damage detection.

CNT-polymer nanocomposites under frictional contact conditions

The unique intrinsic physical properties of Carbon NanoTubes (CNTs) suggest that they are ideal fillers for high-performance composites. Although some experimental studies have revealed the potential of these nanoparticles to tailor the tribological properties of polymer-based composites, the number of theoretical studies on the characterization of their frictional behavior is still very low. This paper is aimed at filling this lacuna by addressing the theoretical analysis of the indentation response of CNT-polymer nanocomposites. To do so, it is first necessary to compute the overall mechanical properties of CNT-polymer composites. Secondly, these properties must be used to evaluate the macroscopic indentation response of the composites. In this work, an extended Mori-Tanaka approach is used to extract the constitutive properties of CNT-polymer nanocomposites. On the basis of ad hoc Eshelby's tensors accounting for particular wavy filler geometries, along with a two-parameter agglomeration model, the homogenization process is performed considering the coupled effect of fillers' waviness and agglomeration. Afterward, a 3D boundary element formulation for contact modeling is applied to study the indentation response of these nanocomposites. The main objective of this paper focuses on analysing the influence of micromechanical features such as fiber content, orientation, waviness, and dispersion on the indentation response of CNT-polymer nanocomposites. Detailed parametric analyses are presented to characterize this phenomenon under frictional contact conditions. The numerical results demonstrate that fillers' waviness and agglomeration have a coupled detrimental effect on the macroscopic response of CNT-reinforced composites.

Predictions of the electro-mechanical response of conductive CNT-polymer composites

We present finite element simulations to predict the conductivity, elastic response and strain-sensing capability of conductive composites comprising a polymeric matrix and carbon nanotubes. Realistic representative volume elements (RVE) of the microstructure are generated and both constituents are modelled as linear elastic solids, with resistivity independent of strain; the electrical contact between nanotubes is represented by a new element which accounts for quantum tunnelling effects and captures the sensitivity of conductivity to separation. Monte Carlo simulations are conducted and the sensitivity of the predictions to RVE size is explored. Predictions of modulus and conductivity are found in good agreement with published results. The strain-sensing capability of the material is explored for multiaxial strain states.

Welding of 3D-printed carbon nanotube-polymer composites by locally induced microwave heating.

Additive manufacturing through material extrusion, often termed three-dimensional (3D) printing, is a burgeoning method for manufacturing thermoplastic components. However, a key obstacle facing 3D-printed plastic parts in engineering applications is the weak weld between successive filament traces, which often leads to delamination and mechanical failure. This is the chief obstacle to the use of thermoplastic additive manufacturing. We report a novel concept for welding 3D-printed thermoplastic interfaces using intense localized heating of carbon nanotubes (CNTs) by microwave irradiation. The microwave heating of the CNT-polymer composites is a function of CNT percolation, as shown through in situ infrared imaging and simulation. We apply CNT-loaded coatings to a 3D printer filament; after printing, microwave irradiation is shown to improve the weld fracture strength by 275%. These remarkable results open up entirely new design spaces for additive manufacturing and also yield new insight into the coupling between dielectric properties and radio frequency field response for nanomaterial networks.

Review and Analysis of Contemporary Polymer Coats based Electromagnetic Shielding Strategies

Objectives: To understand the existing solutions in electromagnetic shielding strategies categorically on polymer coats based solutions to understand gaps and issues in existing solutions. Methods/Statistical analysis: The method adapted for the process is to conduct a detailed review of literature. Many studies were carried out earlier in the domain. Reviewing such studies, the solutions proposed in the earlier contributions and focusing on the research reports that discuss the directions for future course of research in the domain are the priorities. On the basis of inputs gathered from various studies, the information is collated to derive the requisite information. Findings: It is imperative from the study that predominantly the electromagnetic shielding using the polymers was on lead based solutions. Lead based polymers are used for designing the special aprons and solutions that can support in improving the shielding effects. However, one of the key challenges with lead based protective gears are about the increased weight of the apparel and advanced solutions like CNT can be more resourceful for EM shielding. Application/Improvements: CNT is one of the contemporary solution that is explored in the shielding of electromagnetic radiation and if the CNT polymer composites with blended process can increase the efficiency of shielding electromagnetic radiation.

Versatile Electronic Skins for Motion Detection of Joints Enabled by Aligned Few‐Walled Carbon Nanotubes in Flexible Polymer Composites

Here, novel multifunctional electronic skins (E‐skins) based on aligned few‐walled carbon nanotube (AFWCNT) polymer composites with a piezoresistive functioning mechanism different from the mostly investigated theory of “tunneling current channels” in randomly dispersed CNT polymer composites are demonstrated. The high performances of as‐prepared E‐skins originate from the anisotropic conductivity of AFWCNT array embedded in flexible composite and the distinct variation of “tube‐to‐tube” interfacial resistance responsive to bending or stretching. The polymer/AFWCNT‐based flexion‐sensitive E‐skins exhibit high precision and linearity, together with low power consumption (<10 µW) and good stability (no degradation after 15 000 bending–unbending cycles). Moreover, polymer/AFWCNT composites can also be used for the construction of tensile‐sensitive E‐skins, which exhibit high sensitivity toward tensile force. The polymer/AFWCNT‐based E‐skins show remarkable performances when applied to monitor the motions and postures of body joints (such as fingers), a capability that can find wide applications in wearable human–machine communication interfaces, portable motion detectors, and bionic robots.

Thermoelectric characteristics in out-of plane direction of thick carbon nanotube-polystyrene composites fabricated by the solution process

When sheet-like flexible devices are placed on heat sources, a thermal flow is induced along the out-of-plane direction in regards to the device surface. To obtain carbon nanotube-based (CNT-based) thermoelectric devices that work under thermal flows along the out-of-plane direction, it is indispensable to fabricate sufficiently thick CNT-based materials that will allow for an out-of-plane temperature difference to occur. Therefore, we investigated the out-of-plane thermoelectric characteristics of thick CNT-polymer composites (thickness=0.74–0.84mm), which were fabricated by over-coating a dense CNT-dispersed solution, and found that the electrical and thermal conductivities of the composites in the out-of-plane direction were significantly lower than those in the in-plane direction, respectively. We observed that the composites’ figure of merit values in the out-of plane direction was approximately one order of magnitude lower than those in the in-plane direction. This anisotropy in the characteristics of thick CNT-polystyrene composites may be caused by the orientation of the CNTs along the in-plane direction. Therefore, the results indicate that controlling the orientation of CNTs in thick composites is a key factor to improve the performance of devices that work on the basis of temperature differences along the out-of plane direction.

Progress in Conductive-Polymer Carbon Nanotube Composites

Carbon nanotube (CNT) has been widely used as a kind of conductive inorganic filler in composites due to its excellent mechanical properties, thermal properties and electrical properties. Unfortunately, a deal of CNT is needed because it tends to agglomerate in matrix polymers. And therefore the researchers need to explore appropriate methods to decrease the usage of CNT for its high price. This paper summaries the recent development progress in carbon nanotube filled conductive polymer composites, in aspects of the approaches how to reduce the usage of CNT and application of biodegradable CNT-polymer composites. In addition, the future developing research direction in conductive polymer composites filled with carbon nanotube was indicated.

Computational homogenization in RVE models with material periodic conditions for CNT polymer composites

RVE models with material periodic conditions are developed in generating a 3D network of fillers within the RVE. Computational homogenization in 3D RVE models is achieved using two approaches. In the first approach, statistical analysis with number of realizations is performed with increasing RVE size of randomly generated CNT within polymer. In statistical analysis, the filler that exceeds the RVE are translated until they find new spatial location within RVE. Simulations with increasing RVE size are performed until the standard deviation of computed apparent property for each RVE size is minimum to predict the critical RVE size. In the second approach, RVE models with material periodic boundary conditions are developed, which involve placing fillers that exceed the RVE into their respective position on the opposite face of RVE as if the RVE is part of a larger network of RVEs. Percolation threshold analysis of CNT filled polymer composites is presented using both computational homogenization approaches. It is demonstrated that computational homogenized models with material periodic conditions are independent of RVE size and provide homogenized results and are computationally efficient compared to statistical models.

Giant Permittivity Polymer Nanocomposites Obtained by Curing a Direct Emulsion.

Near-percolated CNT-polymer composites are promising high-permittivity materials. The main challenge in the field consists of finding compromises that allow high permittivity and low losses in frequency ranges of interest. Using an emulsion approach and optimizing the size of the droplets and the curing procedure, we obtain unprecedented performances and measure giant permittivity larger than 20,000 at 100 Hz along with a conductivity below 10(-4) S/m.

Effects of different functionalization schemes on the interfacial strength of carbon nanotube polyethylene composite

The mechanical performance of carbon nanotube (CNT) reinforced polymer composites is primarily controlled by the dispersive capacity and interfacial shear strength of CNTs in polymer matrices. CNT functionalizations will improve dispersion and strengthen interfacial bonding of CNTs in matrices. To understand the effects of different functionalization schemes on the interfacial strength of CNT-polymer composites, pullout of the covalent, noncovalent, and mixed functionalized single-walled carbon nanotube (SWCNT) from polyethylene (PE) matrix was simulated by using molecular dynamics, respectively. The results show that the SWCNT-PE interfacial shear strength is significantly improved by SWCNT functionalizations, particularly by mixed functionalization.

Performance of passively Q‐switched ring erbium‐doped fiber laser using a multiwalled carbon nanotubes polyethylene oxide (PEO) polymer composite‐based saturable absorber

ABSTRACTThe aim of this article is to report the fabrication and characterization of dispersed multiwalled carbon nanotubes (MWCNTs) polymer composites and use them as passive SAs in Q‐switched Erbium‐doped fiber (EDF) for ultrafast laser generation at 1.5‐µm region. CNT polymer composites were fabricated into thin films by homogenizing different concentrations (1.8, 4.8, and 10.1 wt. %) of MWCNTs with host polymers polyethylene oxide. The fabricated thin film was then deposited between two fiber connectors as passive SA and incorporated into fiber laser's ring oscillator. The EDFL exhibited a central wavelength of 1560.5 nm when pump power is fixed at 42 mW. The Q‐switching operation starts at the lowest threshold of 39.3 mW for all the three different SA concentrations. For 1.8 wt. % MWCNTs concentration, the pulse repetition rate of the Q‐switched EDFL is started from 35.6 kHz, while for 4.8 wt. % and 10.1 wt. %, the pulse repetition rate started at 78.5 and 66.1 kHz, respectively. At the MWCNTs concentration of 1.8 wt. %, the pulse energy of the Q‐switched EDFL increases from 7.9 to 24.7 nJ as the pump power increases from 39.3 to 58.8 mW. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:1897–1901, 2015

An Enhanced Microstructure-Level Finite Element Machining Model for Carbon Nanotube-Polymer Composites

During the machining of carbon nanotube (CNT)-polymer composites, the interface plays a critical role in the load transfer between polymer and CNT. Therefore, the interface for these composites has to be explicitly considered in the microstructure-level finite element (FE) machining model, so as to better understand their machinability and the interfacial failure mechanisms. In this study, a microstructure-level FE machining model for CNT-polymer composites has been developed by considering the interface as the third phase, in addition to the polymer and the CNT phases. For the interface, two interfacial properties, viz., interfacial strength and fracture energy have been included. To account for variable temperature and strain rate over the deformation zone during machining, temperature and strain rate-dependent mechanical properties for the interface and the polymer material have also been included in the model. It is found that the FE machining model predicts cutting force within 6% of the experimental values at different machining conditions and CNT loadings. The cutting force data reveals that the model can accurately capture the CNT pull-out/protrusion, and the subsequent surface damage. Simulated surface damage characteristics are supported by the surface topographies and roughness values obtained from the machining experiments. The study suggests that the model can be utilized to design the new generation of CNT-polymer composites with specific interfacial properties that minimize the surface/subsurface damage and improve the surface finish.