Multi-walled Carbon Nanotube Composite Films Research Articles

Flexible piezoelectric sensor based on polyvinylidene fluoride/polyacrylonitrile/carboxy-terminated multi-walled carbon nanotube composite films for human motion monitoring

Flexible piezoelectric devices have attracted much attention in the fields of intelligent devices and biomedicine because of their high sensitivity, stability, and flexibility. In this paper, a multifunctional flexible pressure sensor was prepared by adding polyacrylonitrile (PAN) and carboxylic-terminated multi-walled carbon nanotubes (c-MWCNTs) with polyvinylidene difluoride (PVDF) as the substrate. The β-phase content of PVDF/PAN blended fibers compounded with c-MWCNT was up to 95%. At the same time, when PAN was added, the mechanical properties of the composite fibers were constantly improved. The results show that the polymer blending method can improve the comprehensive properties of PVDF composite. The flexible sensor prepared from the PVDF/PAN/c-MWCNT composite film has an output voltage of 2.1 V and a current of 7 μA. The addition of c-MWCNT can largely improve the sensitivity of the sensor (4.19 V N−1). The sensor is attached to the finger and shows good output performance under different degrees of bending of the finger. The maximum output voltage of the sensor is 0.4 V, 0.56 V and 1.15 V when the finger bending angle is 30°, 60°, and 90°, respectively. Moreover, the developed piezoelectric sensor can monitor large-scale movements of various parts of the human body. Therefore, this composite material shows potential in areas such as motion monitoring and energy storage devices.

A V2O5/MWCNTs composite thin film gas sensor for the fast detection of ammonia

In the present study, we develop a new ammonia gas sensor by using sol-gel method and post annealing process. The structure, morphology, and composition of the gas sensor have been characterized by SEM, XRD, XPS, and Raman. The results prove that the V2O5/MWCNTs (multi-walled carbon nanotubes) composite thin film was successfully deposited on alumina substrate. By comparing the responses of the gas sensor to ammonia gas at different temperatures, we find out that the sensor shows good response and excellent response time to ammonia gas at 200 ℃. At this temperature, the sensor exhibits a response of 20% for 100 ppm of ammonia gas with a response time of only 8 s. We find its response time is better than that of ammonia sensors based on single V2O5 or MWCNTs materials. The outstanding sensitivity and unique response curve can be mainly attributed to the semiconductor properties of the two materials and the formation of P-N heterojunction at their interface.

Free-standing polymer/multiwalled carbon nanotubes composite thin films for high thermal conductivity and prominent EMI shielding

Lightweight composite materials with efficient thermal conductivity (TC) and high electromagnetic interference (EMI) shielding effectiveness (SE) are of paramount importance for a wide range of applications such as electronics, aerospace, and stealth technology. In this work, lightweight, flexible, and free-standing poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP)/multiwalled carbon nanotube (MWCNT) composite thin films are fabricated by a single-step, solution casting method. Fabricated PVDF-HFP/MWCNT composite thin films are characterized by many physicochemical techniques such as Raman spectra, Fourier transform infrared spectra, X-ray diffractometer, and high-resolution transmission electron microscope. The resulting composite thin film exhibits a TC of 1.1 Wm−1K−1 at room temperature. Further analysis shows that the TC of the composite film is increased up to 1.8 Wm−1K−1 at 100 °C. As fabricated flexible and free-standing composite thin film (thickness ∼ 150 µm) exhibit an excellent EMI SE of ∼ 36 dB in the X-band region (8.2–12.4 GHz) at just 15 wt. % loading of MWCNT. The outstanding EMI shielding and high TC of PVDF-HFP/MWCNT composite films are attributed to the homogenous distribution and well-connected network of MWCNT within the polymer matrix, forming a conductive network throughout the composite film.

Carbon nanotube films embedded with Cu@C nanocubes for electromagnetic interference shielding

AbstractFlexible carbon tube films for electromagnetic interference (EMI) shielding are assembled by mixing the well‐aligned Cu@C core‐shell nanocubes with multi‐walled carbon nanotubes (MWCNTs). The Cu@C core‐shell nanocubes are achieved by the thermal pyrolysis of polyvinylpyrrolidone (PVP) coating on Cu2O nanocubes. With the optimal PVP concentration of 1.5 mg/mL, the Cu@C/MWCNTs composite film with ultra‐thin thickness (52.2 μm) displays good conductivity of 12.5 S cm−1 and excellent specific EMI shielding value of 510.73 dB mm−1, which is higher than the pure MWCNTs film (439.50 dB mm−1) under the same weight condition. Moreover, the 1.5 mg/mL‐Cu@C/MWCNTs composite film exhibits highly mechanical repeatability after being bended for 10,000 cycles. The carbon layers protecting metal nanoparticles can partly replace precious carbon nanotubes to construction highly flexible composite film with anticipated electrical conductivity, which have a good application prospect for thin, lightweight and flexible EMI shielding fields.

A novel catechin electrochemical sensor based on a two-dimensional MOFs material derivative Zn doped carbon nanosheets and multi-walled carbon nanotubes composite film

In this paper, the precursor ZIF-8/NaCl composite material was successfully synthesized by the in-situ synthesis method, and the two-dimensional zinc doped carbon nanosheets (Zn CNs) were obtained after heat treatment of the precursor. Zn CNs were electrodeposited on carboxylated carbon nanotubes (MWCNTs-COOH) modified glass carbon electrode (GCE) to construct an electrochemical sensor for catechins. The materials are characterized using scanning electron microscope, X-ray photoelectron spectroscopy, and nitrogen adsorption-desorption isotherm. Zn CNs/MWCNTs-COOH composite provide the sensor with excellent electrochemical and electrocatalytic performance. Therefore, the sensor has a wide detection range (30.0–738 nM) and a low detection limit (LOD = 10.0 nM) for catechins. The effectiveness of the sensor was also verified in actual sample detection with good stability and accuracy. This study may provide a feasible solution for the detection of catechin.

Construction and characterization of conductive collagen/multiwalled carbon nanotube composite films for nerve tissue engineering

Currently, a growing number of biomaterials have been evaluated to be beneficial to the application of neural tissue engineering. However, their deficient mechanical and electrical properties limit their further application, especially for nerve regeneration. Therefore, the combination of biological matrix and conductive materials has been applied to meet the requirements for nerve tissue engineering. In this work, conductive collagen (COL)/multiwalled carbon nanotube (MWNT) composite films with different MWNT concentrations were developed by the solvent–evaporation method. The effects of rigid MWNT on the structure, mechanical, thermal, and electrical properties of the flexible COL-based film were evaluated. The evaluation of mechanical properties revealed that the tensile strength of the COL/MWNT composite films was almost eight times as high as that of the pure COL film. The electrical property assessment demonstrated that the electrical conductivity of COL/MWNT-0.25% reached 0.45 S/cm, meeting the electrical stimulation conditions required for nerve growth. Furthermore, the cell viability assays revealed that the COL/MWNT composite films were non-cytotoxic and appropriate for cell growth. Our work proved that the conductive COL/MWNT composite films exhibited great potential for nerve tissue engineering application, which provided a novel self-electrical stimulated platform for the treatment of neural injuries.

Fabrication and characterization of electrospun poly(3-aminobenzylamine)/ functionalized multi-walled carbon nanotubes composite film for electrochemical glucose biosensor

Fabrication and characterization of electrospun poly(3-aminobenzylamine)/ functionalized multi-walled carbon nanotubes composite film for electrochemical glucose biosensor

Fabrication of Cu-WO3-functionalised multiwalled carbon nanotubes composite film electrode by direct deposition for sensing application

Development of nano composite film electrodes have been widely researched for its application as sensors, pseudo capacitors and negative electrodes. Different types of metal oxides, nano materials and various deposition techniques were concomitantly employed for fabrication of this type of electrodes. In the present work electroless deposition technique was applied for formation of copper seed layer over flexible poly ethylene substrate and further electrodeposition of WO3-functionalized multi walled carbon nanotube (fMWCNT) on to copper seed layer. Stable conducting films with uniform morphology of WO3-fMWCNT nano composite was formed over flexible copper substrate. The composite film possessed good electrochemical stability as revealed from various electrochemical analysis. The Cu-WO3-fMWCNT films were used as sensor for qualitative analysis of lubricant oils subjected to aging process under controlled conditions. The developed film electrode give good response curve in the impedance spectroscopy technique during the analysis of fresh and aged lubricant oil Different techniques such as X-ray Powder Diffraction, Scanning Electron Microscopy, Energy Dispersive X-Ray analysis with mapping pattern and Fourier Transform Infrared technique was used for characterization of the hybrid film electrode.

Study of enhanced dielectric permittivity of functionalize multiwall carbon nanotube-based polyvinylidene fluoride free-standing film for flexible storage device

We report the dielectric properties of flexible polyvinylidene fluoride (PVDF) and multiwall carbon nanotube (MWCNT) composite films prepared by solution casting route. The Fourier Transform Infrared Spectroscopy (FTIR) and Raman study engraved more dipolar phases within the carboxyl functionalize (f-MWCNT) embedded PVDF composite film. The dielectric permittivity enhances but the dielectric loss reduces for f-MWCNT embedded PVDF film compared to pristine MWCNT (p-MWCNT) embedded film. The dipolar interaction between –CF2 groups in PVDF and –COOH groups of CNT plays a crucial role in enhancing the dielectric constant. The resistance-voltage plot engraves the formation of the hysteresis loop of the nanocomposite film. The enhanced dielectric permittivity and appearance of a hysteresis loop in f-MWCNT embedded PVDF film can be utilized as the flexible storage device material. Apart from the above, the low value of skin depth of the film makes it a promising candidate for designing a flexible electromagnetic shielding membrane.

Rewritable bistable memory device in polymethyl methacrylate carbon nanotube composite films

The rewritable bistable memory characteristics have been studied in polymethyl methacrylate (PMMA) and carboxylated multi-walled carbon nanotubes (CNT) composite films. The sandwich structure FTO/PMMA + CNTs/Ag devices were prepared by spin coating and vacuum evaporation process. The device exhibited rewritable bistable resistive switching with switch-on voltage of ~ − 1.5 V, switch-off voltage of ~ 3.4 V, and a high ON/OFF ratio almost of 105. The rewritable behavior of the FTO/PMMA + CNTs/Ag device has been investigated by the endurance test, retention test, and the write-read-erase-reread multiple-cycle tests. The FTO/PMMA + CNTs/Ag device exhibited good retention performance for 2 × 105 s and underwent 104 read pulses. The conduction mechanism in ON state obeys Ohmic conduction; simultaneously, for OFF state, trap-limited space-charge limited conduction was discovered to be the dominant conduction mechanism.

Electrical, mechanical, and optical changes in MWCNT-doped PMMA composite films

In this study, we report the preparation of poly (methyl methacrylate)/multi-walled carbon nanotube (MWCNT) composite thin films by simple and efficient solution mixing and ultrasonic method and the electrical, optical, and mechanical characterizations. Scattered light intensity ( I sc), tensile modulus ( E), and surface conductivity ( σ) of these composites have increased with the addition of MWCNT into the composite. The observed behavior in electrical, optical, and mechanical properties of the poly (methyl methacrylate)/MWCNT composites was interpreted by site and classical percolation theory. The optical mechanical and electrical percolation thresholds of poly (methyl methacrylate)/MWCNT composites were determined as φ op = 3 wt%, φ m = 0 wt%, and φσ = 5 wt%, respectively. The optical ( t op), mechanical ( t m), and electrical ( t σ) critical exponents were calculated as 2.23, 0.43, and 0.11, respectively. Both the tensile modulus and tensile strength of poly (methyl methacrylate)/MWCNT composites were increased with increasing MWCNT content until it reaches to 10 wt%. However, above φ = 10 wt%, the mechanical properties of the composites were decreased due to the aggregation of MWCNTs, while the toughness does not show a significant change until φ = 10 wt% MWCNT content, whereas it was decreased above this value.

Functionalized Multi-Walled Carbon Nanotubes and Micro Cellulose Reinforced Poly (Vinyl Alcohol) Hybrid Composite Films: Characterization and Reprocessing Performance

The aim of this research paper was to investigate the synergetic effect of micro cellulose and multi-walled carbon nanotubes (MWCNTs) combination on physicochemical, mechanical and reprocessing performance of Poly (Vinyl Alcohol) hybrid composite films. The hybrid composite films production was carried out by the solution casting method, and the reprocessed films were produced using defective (torn, faulty) films from primary production by the same method. The combined use of MWCNTs and micro cellulose improved the hydrophobicity approximately 85% in ratio. After the reprocessing, decreased intensities of the peaks in the FTIR and Raman results confirmed the reduced molecular interaction between all components of the hybrid composite film, moreover, SEM and TEM revealed the negative defects such as agglomeration which caused mechanical strength decrease. The tensile strength of PVA hybrid composite films loaded cellulose/MWCNTs, reached 97 MPa strength value and elongation at break decreased to 33% according to the neat PVA film. The study results revealed that hybridization had a remarkable impact on improving characteristic properties of composite films and reprocessing process might have been compatible with solution casting method.

Preparation of electrospun poly(acrylic acid)/multiwalled carbon nanotubes composite nanofiber for glucose detection

In this study, poly(acrylic acid) and multiwalled carbon nanotubes (PAA/MWNTs) composite nanofiber thin film was prepared on fluorine doped indium tin oxide–coated glass substrate through electrospinning method. The electrospun PAA/MWNTs nanofiber thin film was modified with layer–by–layer (LbL) self–assembled multilayers of glucose oxidase (GOD) and poly(dialyldimethylammoniumchloride) (PDADMAC) prior to employ for glucose detection. The obtained nanofiber thin film was characterized by scanning electron microscopy and electrochemical impedance spectroscopy. The prepared nanofibers thin film shows a good potential for detection of glucose at constant applied potential through an electrochemical method.

A flexible NO2 gas sensor based on polypyrrole/nitrogen-doped multiwall carbon nanotube operating at room temperature

A flexible NO2 gas sensor based on a polypyrrole/nitrogen-doped multi-walled carbon nanotube (PPy/N-MWCNT) composite film was successfully prepared on PI substrates using a combined in situ self-assembly and annealing treatment method. After annealing at 350 °C, the gas sensor exhibited a high response of 24.82% ((Rg−Ra)/Ra×100%) under 5 ppm of NO2, which is 44.12 times greater than that of the unannealed sensor. The PPy/N-MWCNT gas sensor exhibited excellent repeatability, remarkable selectivity, good long-term stability, and acceptable flexibility. Furthermore, the effect of the relative humidity on the gas sensing properties was examined. The excellent gas sensing performances of the sensor were attributed to the enriched adsorption sites due to degradation of the amount of stacked PPy structures on the surface of the N-MWCNTs after the annealing treatment. The results demonstrated that PPy/N-MWCNT composite films are highly promising for potential applications in the field of NO2 gas sensing.

An ingenious strategy for improving humidity sensing properties of multi-walled carbon nanotubes via poly-L-lysine modification

Multi-walled carbon nanotubes (MWCNTs) as one of excellent conductive and poor-hydrophilicity materials are difficult to be directly used in humidity sensing field. In order to obtain MWCNTs with both good semiconducting characteristic and improved humidity sensing performances, MWCNTs composite film via poly-l-lysine (PLL) modification was developed for humidity detection. The humidity sensing properties of the as-fabricated sensor were investigated at room temperature (25 °C) within the relative humidity (RH) range from 0 to 91.5% RH. Due to abundant hydrophilic functional groups and conduction-blocking effect of PLL, the resistive-type humidity sensor based on MWCNTs/PLL film exhibits a good humidity sensing response of 659.97% at 91.5% RH. Especially, the resistance of the humidity sensor displays a clear positive humidity coefficient (PHC) that caused by the swelling effect of PLL. Finally, various potential applications of the humidity sensor were further performed for the real-time monitoring of skin humidity, baby diaper wetting, spatial humidity distribution and human exhaled breath, which provide an ingenious strategy for the practicability of the humidity sensor.

Sensitivity Enhancement of Acetone Gas Sensor using Polyethylene Glycol/Multi-Walled Carbon Nanotubes Composite Sensing Film with Thermal Treatment.

There is a need to develop a chemiresistive gas sensor equipped with a thermostat over a wide area for the sensor, which can protect the sensor from the influence of ambient temperature due to the uniform temperature of the thermostat. In this paper, we demonstrated an acetone gas sensor based on a polyethylene glycol (PEG)/Multi-walled Carbon Nanotubes (MWCNTs) composite film, which was equipped with a thermostat. The sensor was operated at modest working temperatures for sensor sensitivity enhancement. The optimum design of the polyimide-based thermostat with widely uniform thermal distribution was investigated in detail. It was found that the temperature uniformity of the thermostat was achieved using double spiral geometry. The experimental results of the sensor response showed that the PEG/MWCNTs composite film with a moderate working temperature revealed a higher sensitivity than that without thermal treatment. Moreover, the sensing mechanisms of the PEG/MWCNTs composite gas sensor to acetone vapor were studied as well.

High absorption shielding material of poly(phthalazinone etherketone)/multiwall carbon nanotube composite films with sandwich configurations.

Sandwich structure can be induced to achieve excellent electromagnetic interference shielding effectiveness (EMI SE) as is well known. However, how to optimize the structure to achieve performance optimization is still a problem. Herein, a poly(phthalazinone etherketone)/multiwall carbon nanotube (PPEK/MWCNT) composite with homodisperse and high content (15 wt%) of MWCNT was prepared by a water induced phase separation process. A sandwich structure was designed by introducing a wave-transmitting layer between the PPEK/MWCNT composite films. The MWCNT loading of the shielding layer and the wave-transmitting layer thickness (d) were varied to systematically investigate their influence on shielding performance in the X-band (8.2–12.4 GHz). EMI SE shows strong d value dependence. When the shielding layer was fixed, EMI SE showed a trend of decreasing, rising, leveling off and then decreasing again with d value increasing. The d value in the leveling off stage is the best value for performance optimization. The best d value decreased with increasing MWCNT content of the shielding layer. An absorption dominated SE up to 65 dB and a high increment rate of 140% of SE were achieved by optimization of the d value and shielding layer.

Fabrication and Radioactive Heating Simulation of the flying Balloon Based on Carbon Nanotube Freestanding Films

A light-driven flying balloon has been fabricated using multi-walled carbon nanotube (MWNT) composite films, of which thickness and density are approximately 6 µm and 0.5 mg/cm2, respectively. The shape of balloon is a regular tetrahedron with approximately 11 cm length on a side. By irradiating light using a tungsten lamp to the balloon, the balloon can be levitated like a hot-air balloon because the temperature of MWNT film is rapidly increased and the temperature of air inside the balloon is gradually increased. We confirmed that the maximum levitation height is ap-proximately 14 cm during light irradiation. The balloon developed in this study could be utilized for a flying platform of autonomous flying monitoring system.

Simultaneous Electrochemical Detection of Glucose and Non-Esterified Fatty Acids (NEFAs) for Diabetes Management

In this paper, the feasibility of simultaneous electrochemical detection of glucose and non-esterified fatty acids (NEFA) is investigated using enzyme-based biosensors. The detection of glucose is based on ferrocene-Nafion-glucose oxidase (Fc-Nafion-GOx) modified screen-printed electrodes (SPEs). Solutions of Fc-Nafion-GOx were drop casted on SPEs and dried at room temperature allowing immobilisation of GOx entrapped in Nafion polymer with Fc. The detection of NEFA is based on bi-enzyme electrodes fabricated by the layer-by-layer technique applied onto SPEs using multilayers of poly(dimethyldiallyammonium chloride) polymer, multi-walled carbon nanotube composite films, and two enzymes: acyl-CoA synthetase and acyl-CoA oxidase. Oleoyl coenzyme A lithium salt (OACoA) and oleic acid (OA) were used as NEFA of interests because they are two of the most employed markers in clinical tests. Preliminary results demonstrated that enzyme electrodes showed linear response within the physiological concentration range of glucose and OA in human blood plasma as 5 and 1.2 mM, respectively. These results indicate a promising multi-biosensor platform for rapid one-step determination of glucose and NEFA simultaneously. This could lead the way toward the fabrication of glucose-NEFA biosensors, which can be important in diabetes management and early diagnosis.

Influence of functional group on the electrical transport properties of polyvinyl alcohol grafted multiwall carbon nanotube composite thick film

We present a novel technique to obtain a higher or lower value of dielectric constant due to the variation of a functional group on the surface of multiwall carbon nanotube (MWCNTs) for a polyvinyl alcohol (PVA) grafted MWCNT system. We have prepared PVA grafted pristine and different types of functionalized (-COOH, -OH, and -NH2) MWCNT nanocomposite films. The strong interfacial interaction between the host PVA matrix and nanofiller is characterized by different experimental techniques. The frequency variation of the electrical transport properties of the composite films is investigated in a wide temperature range (303 ≤ T ≤ 413 K) and frequency range (20 Hz ≤ f ≤ 1 MHz). The dielectric constant of the amine (-NH2) functionalized MWCNT incorporated PVA film is about 2 times higher than that of the pristine MWCNT embedded PVA film. The temperature variation of the dielectric constant shows an anomalous behaviour. The modified Cole-Cole equation simulated the experimentally observed dielectric spectroscopy at high temperature. The ac conductivity of the composite films obeys the correlated barrier hopping model. The imaginary part of the electric modulus study shows the ideal Debye-type behaviour at low frequency and deviation of that at high frequency. To illustrate the impedance spectroscopy of the nanocomposite films, we have proposed an impedance based battery equivalent circuit model. The current-voltage characteristic shows hysteresis behaviour of the nanocomposite films. The trap state height for all composite films is evaluated by simulating the current density-electric field data with the Poole-Frenkel emission model. This investigation opens a new avenue for designing electronic devices with a suitable combination of cost effective soft materials.