COOHMWCNTs‐induced BiFeO3‐poly(vinylidene fluoride) (PVDF) composites with enhanced dielectric and ferroelectric properties

In this work, flexible three phase composite films were prepared with surface functionalized multi‐walled carbon nanotubes (f‐MWCNTs) and bismuth ferrite (BiFeO₃;BFO) particles embedded into the poly(vinylidene fluoride) (PVDF) matrix via solution casting technique. The properties and the microstructure of prepared composites were investigated using an impedance analyzer and field emission scanning electron microscope. The micro‐structural study showed that the f‐MWCNTs and BFO particles were dispersed homogeneously within the PVDF matrix, nicely seated on the floor of the f‐MWCNTs separately. The dielectric measurement result shows that the resultant composites with excellent dielectric constant (≈96) and relatively lower dielectric loss (<0.23 at 100 Hz). Furthermore, the percolation theory is explored to explain the dielectric properties of the resultant composites. It says that the percolation threshold of f_MWCNTs = 0.9 wt % and the enhancement of the dielectric constant of the composite was also discussed. In addition, the remnant polarization of the un‐poled PVDF‐BFO‐f‐MWCNTs composites (2P_r ～1.34 µC/cm² for 1.1 wt % of f‐MWCNTs) is also improved. These three phase composites provide a new insight to fabricate flexible and enhanced dielectric properties as a promising application in modern electrical and electronic devices. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46002.     

Fabrication and origin of high-k carbon nanotube/epoxy composites with low dielectric loss through layer-by-layer casting technique

The distribution of polarized space charges and their relaxation behavior in high dielectric constant electric conductor/polymer composites are main factors that determine the frequency-dependent dielectric constant and dielectric loss. However, few reports focus on this motif. We present here the dielectric performance and mechanism of a unique kind of composites with multi-layers (coded as [MWCNT/EP]_x, where x refers to the number of layers), fabricated by using layer-by-layer casting technique. Each composite layer with same thickness was composed of multi-walled carbon nanotubes (MWCNTs) and epoxy (EP) resin. When the loading of MWCNTs is 0.5 wt%, the four-layer [MWCNT0.5/EP]₄ material shows the highest dielectric constant (465 at 1 Hz) and low dielectric loss tangent (0.7 at 1 Hz), about 4 and 2.1 × 10⁻² times the values of traditional MWCNT0.5/EP composite, respectively. By investigating the space charge polarization (SCP), Debye polarization and dielectric moduli in [MWCNT/EP]_x materials, the complex relationships and the origin among dielectric constant, dielectric loss, frequency and the content of filler were clearly elucidated. The SCP within each layer is different from that between layers. The greatly improved dielectric properties of [MWCNT/EP]_x materials are believed to be the reinforced SCP and blocked transport of carriers between every two layers.     

COOH?MWCNTs‐induced BiFeO3‐poly(vinylidene fluoride) (PVDF) composites with enhanced dielectric and ferroelectric properties

In this work, flexible three phase composite films were prepared with surface functionalized multi‐walled carbon nanotubes (f‐MWCNTs) and bismuth ferrite (BiFeO₃;BFO) particles embedded into the poly(vinylidene fluoride) (PVDF) matrix via solution casting technique. The properties and the microstructure of prepared composites were investigated using an impedance analyzer and field emission scanning electron microscope. The micro‐structural study showed that the f‐MWCNTs and BFO particles were dispersed homogeneously within the PVDF matrix, nicely seated on the floor of the f‐MWCNTs separately. The dielectric measurement result shows that the resultant composites with excellent dielectric constant (≈96) and relatively lower dielectric loss (<0.23 at 100 Hz). Furthermore, the percolation theory is explored to explain the dielectric properties of the resultant composites. It says that the percolation threshold of f_MWCNTs = 0.9 wt % and the enhancement of the dielectric constant of the composite was also discussed. In addition, the remnant polarization of the un‐poled PVDF‐BFO‐f‐MWCNTs composites (2P_r ～1.34 µC/cm² for 1.1 wt % of f‐MWCNTs) is also improved. These three phase composites provide a new insight to fabricate flexible and enhanced dielectric properties as a promising application in modern electrical and electronic devices. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46002.     

Frequency‐dependent conductivity and dielectric permittivity of polyaniline/CeO2 composites

The PANI/CeO₂ composites were synthesized using in situ deposition technique by placing fine graded CeO₂ in polymerization mixture of aniline. This is the single step polymerization process for the direct synthesis of emeraldine salt phase of polymer. Low frequency dielectric studies were carried out on pressed pellets of PANI/CeO₂ with various concentrations of cerium oxide (10, 20, 30, 40, and 50 wt % of CeO₂ in PANI). The results are interpreted in terms of polarons and bipolarons, which are responsible for the dielectric relaxation mechanism and frequency dependence of conductivity. It is found that a.c. measurements at room temperature may well serve as a parallel way to the time consuming d.c. conductivity versus temperature technique, to detect the thermal degradation of the transport properties in conducting polymers. It is observed that the charge motion via creation/annihilation of polarons and bipolarons increases as the weight percentage of the composite is increased. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1403–1405, 2006     

Study of alternating current impedance analysis and dielectric properties of carbon nanotube‐based polysulfone nanocomposites

Polysulfone (PSU)/multiwalled carbon nanotubes (MWCNTs) nanocomposites containing 0.5–3 wt% of MWCNTs were prepared by solution casting technique. To understand the dispersion behavior of MWCNTs inPSU matrix, high resolution transmission electron microscopy (HRTEM) and field emission scanning electron microscopy (FESEM) were used. Electrical properties of nanocomposites were investigated by analyzing alternating current (AC) impedance spectra. The real part of complex impedance was decreased with increasing carbon nanotubes loading in the PSU matrix, which may be due to increase in conductive networks in the nanocomposite. The complex impedance Nyquist plots for PSU/MWCNTs nanocomposites were characterized by the appearance of a single semicircular arc, whose radii of curvature decreases with increasing MWCNTs loading. The polarization mechanism and the AC conduction mechanism were studied by designing equivalent circuit from impedance data. The dielectric response of PSU/MWCNTs nanocomposite was investigated over a wide range of frequency from 10 Hz to 10⁻⁶ Hz. Dielectric constant of PSU/MWCNTs nanocomposite was enhanced significantly from 2 to 6 × 10¹⁰ at 10 Hz when the addition of MWCNTs was increased from 0 to 3 wt%. The enhancement of dielectric property might be due to the interfacial polarization between carbon nanotubes and polysulfone. POLYM. COMPOS., 2012. © 2011 Society of Plastics Engineers     

The production of carbon nanotube/epoxy composites with a very high dielectric constant and low dielectric loss by microwave curing

Multiwalled carbon nanotube (MWCNT)/epoxy (EP) composites were developed using microwave curing (m-MWCNT/EP). They have a very high dielectric constant and low dielectric loss. For comparison, composites based on the same components were also prepared by thermal curing (t-MWCNT/EP). Results show that the two types of composites have greatly different dielectric properties. With the same content of MWCNTs, m-MWCNT/EP composites show a much higher dielectric constant and lower dielectric loss than t-MWCNT/EP composites. Specifically, the dielectric constant and loss at 100 Hz of m-MWCNT/EP composite with 0.04 vol% MWCNTs are about 2.5 and 0.05 times the corresponding value of t-MWCNT/EP composites, respectively, because of their different structures. Compared with t-MWCNT/EP composites, the nanotubes in m-MWCNT/EP composites not only have a better dispersion in the matrix, but also align in a direction. An equivalent circuit model was set up to evaluate the influence of dispersion and spatial distribution of MWCNTs on the dielectric properties. It shows that it is possible to control the dispersion and spatial distribution of carbon nanotubes using a different curing technique to obtain high performance composites with unexpected dielectric properties, especially those with very high dielectric constant and low dielectric loss.     

Control of Conductive and Mechanical Performances of Poly(Amide‐Imide) Composite Films Utilizing Synergistic Effect of Polyaniline and Multi‐Walled Carbon Nanotube

Functionalized multi‐walled carbon nanotubes (FMWCNTs) have been incorporated into binary composites of poly(amide‐imide) (PAI) and polyaniline (PANI) to improve their conductive and mechanical performances. The conductivity of PAI/PANI/FMWCNTs ternary composites significantly increased from 10^?3 to 8.3 S m^?1 with increasing the weight ratio of FMWCNTs from 0 to 10 wt%, which is much higher than that of the sum of PAI/PANI and PAI/FMWCNTs binary composites. The enhanced conductivity is mainly ascribed to be the more intensive conductive percolating network formed in the PAI/PANI/FMWCNTs ternary composites due to the hydrogen bond interaction among PAI, PANI and FMWCNTs. On the other hand, the tensile strength has been improved by 40% from 25 to 35 MPa. The self‐extinguishing property and phase transition of the ternary films have also been investigated by thermal gravimetric analysis and differential scanning calorimetry, respectively. It is found that the weight ratio of FMWCNTs and the special morphology are the two important factors that induce such unusual properties. POLYM. ENG. SCI., 59:E224–E230, 2019. © 2018 Society of Plastics Engineers     

Simultaneous enhancement of electrical conductivity and interlaminar shear strength of CF/EP composites through MWCNTs doped thermoplastic polyurethane film interleaves

Carbon fiber-reinforced epoxy (CF/EP) composites have been widely used in aerospace industry, while poor electrical conductivity and interlaminar shear fracture toughness could reduce their safety as structural components in use. In this work, we achieved simultaneous improvement in electrical conductivity and interlaminar shear strength through interleaved multi-walled carbon nanotubes (MWCNTs) doped thermoplastic polyurethane (TPU) conductive thin films (CTFs), which were prepared by a solution casting method. The experimental results showed that the electrical conductivity of the laminates increased by about 13 and 16 times in the transverse and thickness directions with only about 1 wt % MWCNTs content in the laminates. The end-notch flexure (ENF) tests showed that the mode II interlaminar fracture toughness (G_IIC) of composites with 10 wt % MWCNTs CTF interleaf shows a significant increase of about 106%. The enhancement mechanism was further explored through microscopic morphological observation. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47988.     

Effects of multi‐walled carbon nanotubes and conductive carbon black on electrical,dielectric, and mechanical properties of epoxidized natural rubber composites

The influence of multi‐walled carbon nanotubes (MWCNTs) and conductive carbon black (CCB) on cure, electrical, dielectric, and mechanical properties of epoxidized natural rubber (ENR) composites was investigated. It was found that short MWCNTs (S‐MWCNTs) with low loading significantly affected the cure characteristics in a way similar to high loading of CCB. Moreover, the ENR/S‐MWCNTs composites exhibited high AC conductivity, dielectric constant, and dielectric loss tangent (tan δ ) compared to the ENR/CCB and ENR/L‐MWCNTs (long MWCNTs) composites. In addition, the S‐MWCNTs composites showed the lowest percolation threshold concentration, defined as the lowest loading to form conductive paths in the insulating ENR matrix. This might be attributed to the comparatively high interfacial polarization, with good dispersion and distribution, of the S‐MWCNTs in ENR matrix. These characteristics were confirmed by TEM imaging and by a high bound rubber content, corroborating strong filler–rubber interactions in the ENR/S‐MWCNTs composites. However, the L‐MWCNTs composites showed the lowest electrical and other related properties, despite the highest aspect ratio and specific surface area of this filler. This might be because of the flocculation of nanotubes by mutual entanglement, leading to a poor uneven distribution in the ENR matrix. POLYM. COMPOS., 38:1031–1042, 2017. © 2015 Society of Plastics Engineers     

Flexible conductive poly(styrene‐butadiene‐styrene)/carbon nanotubes nanocomposites: Self‐assembly and broadband electrical behavior

Flexible conductive nanocomposites with the ability of self‐assembly into well‐ordered structures are promising multifunctional materials for energy conversion and storage devices. In this work, flexible nanocomposites based on multi‐walled carbon nanotubes (MWCNTs) and poly(styrene‐butadiene‐styrene) (SBS) were obtained by solution casting, followed by a post‐annealing treatment, during 7 days at 110 °C, to enable the self‐organization of the SBS. The impact of the MWCNTs on the self‐assembly was studied by atomic force microscopy and Small angle X‐rays scattering, and the conductivity of these nanocomposites was analyzed over the broadband frequency range, that is, 10^?1–10⁶ Hz. The results revealed that the lower MWCNTs loadings (～0.2 v %) were the most suitable to achieve a conductive network through the SBS, maintaining self‐assembled domains. These domains include hexagonally packed cylinders and alternating lamellae. Furthermore, at loadings above 1 v %, the impact of further MWCNTs addition on the conductivity was marginal over the whole frequency range and the self‐assembly tendency was progressively reduced. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46650.     

Synthesis,characterization, and thermo mechanical properties of siloxane‐modified epoxy‐based nano composite

In this study, polymer hybrid composites were synthesized by sol‐gel process. 3‐Amino‐propyltrimethoxysilane [APTMS)/γ‐Glycidoxypropyl trimethoxy‐silane (GPTMS); (4, 4′‐Methylene‐dianiline (DDM)] and 1,4‐Bis(trimethoxysilylethyl) benzene (BTB) were added to DGEBA type epoxy resin for anticipated to exhibit excellent thermal stability. Boron trifluoride monoethylamine (BF₃MEA) was used as catalyst. The structure of nanocomposites was characterized by attenuated total reflectance (ATR) and solid‐state ²⁹Si NMR which suggest EP‐APTMS‐BTB/EP‐GPTMS‐BTB possesses T³; T¹–T⁰, and T¹ structures when the BTB content was lower than 10 wt % and higher 20 wt %, respectively. BF₃MEA was proved to be an effective catalyst for the sol‐gel reaction of APTMS, but it could not promote for GPTMS. From TEM microphotographs, EP‐APTMS‐BTB (10 wt %) possesses a dense inorganic structure (particle size around 5–15 nm) compare with the loose inorganic structure of EP‐GPTM‐/BTB (10 wt %). DSC, TGA were use to analyze the thermal properties of the nanocomposites and DMA was used to analyze the dynamic mechanical properties of hybrid composites. The T_gs of all nanocomposites decreased with the increasing BTB content. A system with BTB content lower than 10 wt % showed good dynamic mechanical property and thermal stability (Td₅ increased from 336°C to 371°C, char yield increased from 27.4 to 30.2%). The structure of inorganic network affects the Td₅ and dynamic mechanical properties of composite. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40984.     

Electrical and dielectric properties of multiwall carbon nanotube/polyaniline composites

In this paper, electrical and dielectric properties of multiwall carbon nanotubes (MWCNTs)/insulating polyaniline (PANI) composites were studied. A mixture of MWCNTs and insulating polyaniline was dispersed in an ethanol solution by ultrasonic process, subsequently dried, and was hot-pressed at 200 °C under 30 MPa. Electrical and dielectric properties of the composites were measured. The experimental results show that the dc conductivities of the composites exhibit a typical percolation behavior with a low percolation threshold of 5.85 wt.% MWCNTs content. The dielectric constant of the composites increases remarkably with the increasing MWCNTs concentration, when the MWCNTs concentration was close to percolation threshold. This may be attributed to the critical behavior of the dielectric constant near the percolation threshold as well as to the polarization effects between the clusters inside the composites.     

Fabrication and dielectric properties of poly(ether ether ketone)/polyimide blends with selectively distributed multi‐walled carbon nanotubes

The distribution and contents of conductive fillers have a decisive influence on the dielectric properties of polymer/conductive filler composites. Herein, we clarified how the phase morphology and filler contents affect the dielectric properties of poly(ether ether ketone) (PEEK)/polyimide (TPI)/multi‐walled carbon nanotubes (MWCNTs) composites, in which MWCNTs were selectively located in the TPI phase. Firstly, PEEK/TPI/MWCNTs composites with identical MWCNTs content but different PEEK/TPI ratios were prepared. The composites with co‐continuous phase structure exhibited much better dielectric properties than those with sea–island structure. Then, PEEK/TPI/MWCNTs composites with the same PEEK/TPI ratio but various MWCNTs contents were prepared. The dielectric constant of the composite with 2 wt% MWCNTs reached 11306, which is because the formation of a co‐continuous phase structure benefited the mini‐capacitor network. Our results provide an effective method to develop high‐dielectric‐constant composites using the concept of double percolation. © 2015 Society of Chemical Industry     

Carbon nanotubes/polyaniline nanocomposite coatings: Preparation,rheological behavior,and their application in paper surface treatment

Conventional cellulosic paper, rendered electro‐conductive, may hold considerable promise for diversified applications in such areas as electro‐magnetic interference shielding and energy storage. Here, an electro‐conductive cellulosic paper was prepared by surface application of multi‐walled carbon nanotubes (MWCNTs)/polyaniline (PANI) nanocomposites onto a conventional base paper. MWCNTs/PANI nanocomposites were prepared by in situ polymerization of aniline with different contents of MWCNTs and used as electro‐conductive filler for the fabrication of electro‐conductive surface‐coated paper. The achieved MWCNTs/PANI nanocomposites exhibited a core‐shell structure, as evidenced by TEM. Effects of feeding ratios of MWCNTs on the rheological behavior of nanocomposite coatings, as well as the mechanical properties and electrical conductivity of surface‐coated paper were studied. Results revealed that the rheological behavior of the nanocomposite coatings showed strong dependence on the MWCNTs content. Moreover, both the electro‐conductivity and mechanical properties of surface‐coated paper were improved as a function of surface application of MWCNTs/PANI nanocomposites, particularly, in presence of an optimum content of MWCNTs. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46329.     

Copper chloride‐doped polyaniline/multiwalled carbon nanotubes nanocomposites: Superior electrode material for supercapacitor applications

In this study, copper chloride (CuCl₂)‐doped polyaniline (PANI)/multiwalled carbon nanotubes (MWCNTs) nanocomposite (PANI C2 CNT), CuCl₂‐doped PANI (PANI C2) and pure PANI was synthesized by in situ oxidative polymerization method, using ammonium peroxodisulfate as oxidant in HCl medium. These composites were investigated as electrode materials for supercapacitors. The interaction of metal cation (Cu²⁺) with PANI was confirmed by Fourier transform infrared spectroscopy. The morphology of the composites was characterized by field‐emission scanning electron microscopy and high‐resolution transmission electron microscopy analysis. Electrochemical characterizations of the materials were carried out by three electrode probe method, where platinum and saturated standard calomel electrode were used as counter and reference electrode, respectively. 1 M KCl solution was used as electrolyte for all the electrochemical characterizations. The transition metal ion doping enhanced the electrochemical properties of the conducting polymer. Among all the composites, CuCl₂‐doped PANI/MWCNT showed highest specific capacitance value of 724 F/g at 10 mV s⁻¹ scan rate. The Nyquist plot of the polymeric materials showed low equivalent series resistance of the electrode materials. Thermal stability of the composites was examined by thermogravimetric analysis.POLYM. COMPOS., 2013. © 2013 Society of Plastics Engineers     

Preparation and characterization of composites of polyaniline nanorods and multiwalled carbon nanotubes coated with polyaniline

Composites of polyaniline (PANI) nanorods and multiwalled carbon nanotubes (MWNTs) coated with PANI were prepared by in situ polymerization with perchloric acid as a dopant. Transmission electron microscopy images showed that the coexisting composites of PANI nanorods and MWNTs coated with PANI were formed at low MWNT contents. The interaction between MWNTs and PANI was proved by Fourier transform infrared and ultraviolet–visible spectra. The electrical conductivity of a dedoped PANI/MWNT composite with a 16.3 wt % concentration of MWNTs reached 3.0 × 10^?3 S/cm, which was 6 orders of magnitude higher than that of dedoped PANInanorods. The results also showed that coexisting composites of PANI nanorods and MWNTs coated with PANI had high electrochemical activity and good cyclic stability. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Modified carbon nanotube composites with high dielectric constant, low dielectric loss and large energy density

Flexible dielectric polystyrene based composites containing multi-walled carbon nanotubes (MWCNTs) were reported. The MWCNTs were coated with polypyrrole (PPy) by an inverse microemulsion polymerization. Transmission electron microscopy, X-ray photoelectron spectroscopy and Raman spectroscopy indicated that the MWCNTs were coated with PPy. Our composites presented a stable high dielectric constant (∼44), rather low loss (<0.07), and large energy density (up to 4.95 J cm⁻³). The largely-enhanced dielectric performance originates from the organic shell PPy, which not only ensure good dispersion of MWCNTs in the polymer matrix but also screen charge movement to shut off leakage current. Such MWCNT composites can be used to store charge and electrical energy and play a key role in modern electronics and electric power systems.     

Conductivity and mechanical properties of composites based on MWCNTs and styrene‐butadiene‐styrene block™ copolymers

Composites based on multiwall carbon nanotubes (MWCNTs) and the block copolymer styrene‐butadiene‐styrene with two different contents of styrene have been investigated and their electrical conductivity and mechanical properties have been evaluated. The composites were prepared by a solution casting procedure, using a dispersant agent for the MWCNTs. Conductivity values of 10^?4 and 1.6 S cm^?1 have been obtained for samples containing 1 and 12 wt % of MWCNTs, respectively. The percolation threshold achieved for these systems was ～0.25 wt %. According to dynamic mechanical analysis, the MWCNTs interact with both phases of the copolymers, acting as a reinforcement filler, whereas the dispersant agent acts as a plasticizer. However, it was shown that the reinforcing effect of the MWCNTs overcomes the latter, resulting in an overall improvement of mechanical properties of the composites. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Fabrication and electrochemical characterization of polyaniline nanorods modified with sulfonated carbon nanotubes for supercapacitor applications

The novel composites of sulfonated multi-walled carbon nanotubes (sMWCNTs) modified polyaniline (PANI) nanorods (PANI/sMWCNTs) were synthesized successfully by in situ oxidative polymerization method in the HClO₄ solution. FTIR and Raman spectra revealed the presence of π–π interaction between the PANI and the sulfonated carbon nanotubes and the formation of charge transfer composites. It was found that the specific capacitance of the PANI/sMWCNT composites was markedly influenced by their morphological structure and the content of PANI which was coated onto the sMWCNT. The specific capacitance of the PANI/sMWCNT composite exhibited a maximum value of 515.2 F g⁻¹ at the 76.4 wt% PANI. The charge–discharge tests showed the PANI/sMWCNT composites possessed a good cycling stability (below 10% capacity loss after 1000 cycles) compared to PANI nanorods.     

Property reinforcement of acrylonitrile‐butadiene‐styrene by simultaneous incorporation of carbon nanotubes and self‐prepared copper particles

In this article, copper (Cu) crystallites were successfully prepared via low temperature molten salt method, and the possible formation mechanisms were proposed. The conductive fillers of multiwalled carbon nanotubes (MWCNTs) and as‐prepared Cu particles were designed and introduced into acrylonitrile‐butadiene‐styrene (ABS) blend to prepare different conductive composites. The dispersion states of conductive fillers and the morphologies of the composites were characterized using a field emission scanning electron microscope. The electrical resistivity of different composites was measured. The results showed that Cu and MWCNTs exhibited a synergistic effect in decreasing the electrical resistivity of the Cu/MWCNTs/ABS composites, because Cu that could locate between MWCNTs chain segments provides a better charge transport in the conductive pathways. Compared with pure ABS, the tensile strength, elastic modulus and thermal stability of the Cu/MWCNTs/ABS composites were significantly improved with the incorporation of Cu and MWCNTs. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41738.