Electrical and rheological percolation in poly(vinylidene fluoride)/multi‐walled carbon nanotube nanocomposites

Nanocomposites of poly(vinylidene fluoride) (PVDF) and multi‐walled carbon nanotubes (MWCNTs) were prepared through melt blending in a batch mixer (torque rheometer equipped with a mixing chamber). The morphology, rheological behavior and electrical conductivity were investigated through transmission electron microscopy, dynamic oscillatory rheometry and the two‐probe method. The nanocomposite with 0.5 wt% MWCNT content presented a uniform dispersion through the PVDF matrix, whereas that with 1 wt% started to present a percolated network. For the nanocomposites with 2 and 5 wt% MWCNTs the formation of this nanotube network was clearly evident. The electrical percolation threshold at room temperature found for this system was about 1.2 wt% MWCNTs. The rheological percolation threshold fitted from viscosity was about 1 wt%, while the threshold fitted from storage modulus was 0.9 wt%. Thus fewer nanotubes are needed to approach the rheological percolation threshold than the electrical percolation threshold. Copyright © 2010 Society of Chemical Industry     

Preparation and characterization of poly(vinylidene fluoride) nanocomposites containing multiwalled carbon nanotubes

Poly(vinylidene fluoride) (PVDF) nanocomposites with different loadings of multiwalled carbon nanotubes (MWNT) were prepared by melt‐compounding technique. A homogeneous dispersion of MWNT throughout PVDF matrix was observed on the cryo‐fractured surfaces by scanning electron microscopy. Thermogravimetric analysis results indicated that the thermal stability of neat PVDF was improved with the incorporation of MWNT. Dynamic mechanical analysis showed a significant improvement in the storage modulus over a temperature range from ?125 to 75°C with the addition of MWNT. The melt‐rheological studies illustrated that incorporating MWNT into PVDF matrix resulted in higher complex viscosities (|η*|), storage modulus (G′), loss modulus (G″), and lower loss factor (tan δ) than those of neat PVDF. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Nanocomposites of poly(vinylidene fluoride) with multiwalled carbon nanotubes

The preparation and characterization of nanocomposites of poly(vinylidene fluoride), PVDF, with acid treated multiwalled carbon nanotubes (MWCNT) with a wide composition range, from 0.1 to 5.0% MWCNT by weight, is reported. Effect of uniaxial orientation by zone drawing on these nanocomposites is discussed and compared with unoriented compression molded films. Static room temperature two‐dimensional wide angle X‐ray scattering and Fourier transform infrared spectroscopy were used for phase identification. Differential scanning calorimetry, polarizing optical microscopy, dynamic mechanical analysis (DMA), and thermogravimetic analysis (TGA) were used to study the thermal and mechanical properties. Incorporation of MWCNT into PVDF has no obvious effect in forming beta phase crystal in the PVDF/MWCNT bulk films, while zone drawing cause a significant alpha to beta transition in PVDF/MWCNT. Results indicate that MWCNTs act as nucleation agent during crystallization and slightly increase the degree of crystallinity of PVDF/MWCNT bulk films. TGA indicates the thermal stability is improved when MWCNT concentration increases for unoriented PVDF/MWCNT film. The modulus also increases significantly when MWCNT concentration increases. The glass transition temperature measured by the peak position of tanδ from DMA does not change with MWCNT concentration, but a slightly higher glass transition can be obtained by zone drawing. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Morphology and physical properties of nanocomposites based on poly(methyl methacrylate)/poly(vinylidene fluoride) blends and multiwalled carbon nanotubes

Nanocomposites of blends of poly(vinylidene fluoride) (PVDF) and poly(methyl methacrylate) (PMMA) with multiwalled carbon nanotubes (CNTs) were prepared by melt mixing and hot press molding followed by quenching or annealing (120°C, 24 h). PMMA‐rich nanocomposites showed higher electrical conductivity than PVDF‐rich samples at identical CNT loading. At a specific composition, the quenched nanocomposites showed electrical conductivity values three to four orders of magnitude higher than those observed in annealed samples. Measurement of the dielectric constants also supported the electrical conductivity results. In the annealed samples, agglomerated CNTs located mainly in the PVDF crystalline phase were observed. Addition of CNTs promoted the crystallization, and especially, the formation of β‐crystals, which was confirmed by X‐ray diffraction. The thermal behavior of nanocomposites from differential scanning calorimetry (DSC) analysis was explained in terms of the three‐phase model involving the presence of the rigid amorphous fraction, the mobile amorphous fraction, and the crystalline phase. POLYM. COMPOS., 36:1195–1204, 2015. © 2014 Society of Plastics Engineers     

Effect of multi‐walled carbon nanotubes on crystallization,thermal, and mechanical properties of poly(vinylidene fluoride)

Composites were prepared by solution blending poly(vinylidene fluoride) (PVDF) and multi‐walled carbon nanotubes (MWNTs). Fourier transform infrared spectroscopy (FTIR) and X‐ray diffraction (XRD) results showed that the crystalline structure of PVDF was changed by the addition of MWNTs and a MWNTs‐induced crystal transformation from α‐phase to β‐phase of PVDF was confirmed. With differential scanning calorimeter (DSC) and dynamic mechanic thermal analysis (DMA) techniques, thermal and mechanical properties of the composite films were examined. As the DSC results showed, addition of MWNTs would lead to the increased cooling crystallization temperature (T_c), implying that MWNTs nanoparticles could act as nucleating agents, which is further proved with the help of polarized optical microphotographs. On the other hand, the decreasing of D_d (degree of crystallinity) implied that the MWNTs networks can confine the crystallization of PVDF. Through the curve analysis of the dynamic mechanical measurements, it was found that the storage modulus (E′) is significantly enhanced, revealing that a strong interaction should exist between PVDF and MWNTs. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Exceptional dielectric properties of chlorine-doped graphene oxide/poly (vinylidene fluoride) nanocomposites

Herein, we report a facile method to significantly enhance the dielectric performance of reduced graphene oxide-based polymer composites. Addition of thionyl chloride into graphene oxide (GO) dispersion induces synergistic modifications of the structure, chemistry, charge carrier density and electrical conductivity of GO, as well as the interfacial interaction and phase of the surrounding matrix in the poly (vinylidene fluoride) (PVDF) composite. The composites reinforced with a very low reduced chlorinated GO (Cl-rGO) content of 0.2 vol% deliver an exceptional dielectric constant of 364 with a moderate dielectric loss of 0.077 at 1 kHz. These values are well contrasted with the corresponding properties of the neat PVDF polymer with a constant of 28 and a loss of 0.0029. Synergistic effects arising from chlorination are identified, including the much enhanced electrical conductivity of Cl-GO sheets by more than 3 orders of magnitude through introducing charge-transfer complexes, the improved interfacial interactions between the fillers and the PVDF matrix through hydrogen bonds, and the transformation of PVDF to β-phase with an inherently high dielectric constant due to dipolar interaction. The comparison with the literature data confirms superior dielectric performance of the present Cl-rGO/PVDF composites.     

多壁碳纳米管/聚酰亚胺复合材料制备及其性能研究

聚酰亚胺的前聚体,聚酰胺酸,是通过4,4-二氨基二苯醚(ODA)与3,3,4,4二苯甲酮四羧酸二酐(BTDA)反应制备的.未改性的、酸改性和胺改性的多壁碳纳米管(MWCNT)被分别地单独加入到聚酰胺酸溶液中,并加热至300℃,从而制成聚酰亚胺/碳纳米管复合材料.扫描型电子显微镜(SEM)和透射电子显微镜(TEM)的显微...     

New piezoelectric damping composites of poly(vinylidene fluoride) blended with clay and multi‐walled carbon nanotubes

Damping materials are used to control mechanical vibrations, and piezoelectric damping composite is a very promising material due to its unique mechanism. In this study, a potential piezoelectric damping composite was developed by simply melt mixing poly(vinylidene fluoride) (PVDF) with small amounts of organic modified montmorillonite (OMMT) and multi‐walled carbon nanotubes (MWCNTs). The piezoelectric, mechanical and electrical properties were investigated using a dynamic mechanical analyser, direct current electrical resistivity measurements, X‐ray diffraction, Fourier transform infrared spectroscopy and the direct quasi‐static d₃₃ piezoelectric coefficient method. It was found that the damping property of PVDF can be greatly improved by adding both MWCNTs and OMMT, and the composite containing 1.9 wt% of MWCNTs and 3 wt% of OMMT showed the best damping property. A model and an approximate calculation were applied to explain the improved damping property. Moreover, similar mechanical properties of PVDF composites were observed in the tensile testing and dynamic mechanical analyser measurements. Copyright © 2012 Society of Chemical Industry     

Coaxial electrospun nanofibers of poly(vinylidene fluoride)/polyaniline filled with multi‐walled carbon nanotubes

Core‐shell nanofibers of poly (vinylidene fluoride)/polyaniline/multi‐walled carbon nanotubes (PVDF/PANi/MWCNTs) have been produced using the coaxial electrospinning technique. The nanofibers were semiconductive and had better piezoelectric properties than pure PVDF nanofibers. Piezoelectric PVDF nanofibers are capable of converting mechanical energy into electrical energy, which can be stored in charge storage devices. However, PVDF is not conductive and therefore, a conductive associate material is needed to transfer accumulated static charges into the capacitor. Fourier Transform Infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC) were carried out to study the crystalline β‐phase of PVDF. There was an increase in β‐phase in the electrospun PVDF nanofibers filled with MWCNTs as compared with compression molded samples of neat PVDF. Incorporation of PANi as an intrinsically conductive polymer (ICP) and MWCNTs as conductive nanofiller helps the movement of static charges. Core‐shell nanofibers had conductivities of about seven orders of magnitude higher than simple electrospun nanofibers. POLYM. COMPOS., 35:1198–1203, 2014. © 2013 Society of Plastics Engineers     

Hydrogen sulfide sensing properties of multi walled carbon nanotubes

This paper investigates the effect of functional groups on the hydrogen sulfide sensing properties of multi-walled carbon nanotubes using carboxyl and amide groups and Mo and Pt nanoparticles as decorated precursors in gaseous state at working temperature. Carbon nanotubes were synthesized by the CVD process and decorated with the nano particles; provide higher sensitivity for H₂S gas detection. The MWCNTs were characterized by scanning electron microscopy combined with energy dispersive X-ray (SEM/EDX), transmission electron microscopy (TEM), X-ray diffraction (XRD), ATR-IR absorption and Fourier transforms infrared (FT-IR) analyses. The MWCNTs were deposited as a thin film layer between prefabricated gold electrodes on alumina surfaces. The sensitivity of carbon nanotubes was measured for different H₂S gas concentrations and at working temperature. The results showed that the measured electrical conductance of the modified carbon nanotubes with functional groups is modulated by charge transfer with P-type semiconducting characteristics and metal decorated carbon nanotubes exhibit better performances compared to functional groups of carboxyl and amide for H₂S gas monitoring at room temperature.     

Graphene nanocomposites based on poly(vinylidene fluoride): Structure and properties

A nanocomposite of Poly(vinylidene fluoride) (PVDF) was prepared with graphene sheets (GSs), which are a novel filler by a solution method. The structure‐properties relationships of PVDF/GSs nanocomposites were studied. The results of differential scanning calorimetry and X‐ray diffraction show that addition of GSs to the PVDF matrix promotes an α phase to β phase transformation of the polymer crystal. The nanocomposites exhibit significant increases in dynamic mechanical properties and thermal stability compared to the neat PVDF. In addition, the incorporation of GSs in PVDF indicated excellent optical transparency at the lowest weight fractions of GSs and modified wettability of PVDF. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Electrical conductivity of carbon nanotube/poly(vinylidene fluoride) composites prepared by high-speed mechanical mixing

Electrically conductive multi-walled nanotube (MWCNT)/poly(vinylidene fluoride) (PVDF) composites with a segregated structure were prepared by high-speed mechanical mixing method. It was found that MWCNTs were uniformly dispersed on polymer particle surfaces. At the MWCNTs composition of 0.1 vol.%, the composites exhibited a dramatic enhancement in electrical conductivity by 11 orders of magnitude. A low percolation threshold was achieved at the CNT concentration of 0.078 vol.%. The mechanical mixing method presented can be adapted to other CNT/polymer composites with a segregated structure.     

Preparation and properties of single-walled carbon nanotubes/poly(butylene terephthalate) nanocomposites

A neat poly(butylene terephthalate) (PBT) polymer and functionalized single-walled carbon nanotubes (F-SWNTs)/PBT nanocomposite films were prepared by solution casting technique. The SWNTs were functionalized by acid treatment, which introduced carboxylic groups onto the SWNTs. The morphological studies showed that the F-SWNTs were embedded and dispersed well within the PBT polymer matrix. The POM study illustrated that a neat PBT showed Maltese-type spherulites. It was also observed that the size of neat PBT spherulites was larger than F-SWNTs/PBT nanocomposite spherulites, which might be due to the nucleation effect of F-SWNTs in the case of nanocomposites. The thermal stabilities and mechanical properties such as stress yield and moduli of F-SWNTs/PBT nanocomposites were enhanced as compared to neat PBT. The DSC study showed that the melting temperature (T _m) of PBT was slightly increased by addition of F-SWNTs. This increase in T _m might be due to the formation of compact structure, which was formed through different types of molecular interactions with addition of F-SWNTs. It was also found that initially the solvent (distilled water, kerosene, 2 M HNO₃ solution) uptake by neat PBT polymer and its nanocomposites increased gradually, which became steady after specific intervals for each sample. The results also exhibited that the solvent uptake of F-SWNTs/PBT nanocomposites was less than neat PBT.     

Dielectric properties of poly(vinylidene fluoride) composites based on Bucky gels of carbon nanotubes with ionic liquids

“Bucky gels” of carbon nanotubes were successfully prepared by grinding multi‐walled carbon nanotubes (MWNTs) and ionic liquids (ILs) for several hours. A series of poly(vinylidene fluoride) (PVDF) composites with Bucky gels was obtained through simple melt compounding. The Raman spectrum showed significant interaction among the ILs, MWNTs, and PVDF. The dielectric behavior of the PVDF composites based on unmodified and IL‐modified MWNTs was studied from 40 Hz to 30 MHz. The addition of ILs significantly enhanced the dielectric property of the PVDF/IL/MWNT ternary composites, which was much higher than that of the sum of PVDF/IL and PVDF/MWNT binary composites. The SEM results revealed that both MWNTs and ILs uniformly dispersed throughout the PVDF/IL/MWNT composites because of the strong interaction between them. The DSC and XRD results showed that the addition of ILs in the composites changed the crystallinity and crystal form of the PVDF. POLYM. COMPOS., 36:94–101, 2015. © 2014 Society of Plastics Engineers     

Crystal transformation and thermomechanical properties of poly(vinylidene fluoride)/clay nanocomposites

The crystal transformation and thermomechanical properties of melt‐intercalated poly(vinylidene fluoride) (PVDF)/clay nanocomposites are reported in this study. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were used to study the thermal properties of PVDF and its nanocomposites with various clay concentrations. The incorporation of clay in PVDF results in the formation of β‐form crystals of PVDF. DSC study of melting behavior suggested the presence of only α‐phase crystals in neat PVDF and both α‐ and β‐phase crystals in the nanocomposite. This conclusion was corroborated by findings from Fourier‐transform infrared (FTIR) spectroscopy and X‐ray diffraction (XRD). Dynamic mechanical analysis (DMA) indicated significant improvements in storage modulus over a temperature range of 20–150 °C. The coefficient of thermal expansion (CTE) decreases with increasing clay loading. Copyright © 2004 Society of Chemical Industry     

Electrical characteristics of fluorinated carbon black‐filled poly(vinylidene fluoride) composites

Dispersion and electrical properties of fluorinated carbon black‐filled poly(vinylidene fluoride) (PVDF) composites were studied as a function of the fluorine content. It was found that with increasing the fluorine content carbon particles tend to stick together to form large aggregates. The percolation concentration increases to a high concentration, whereas the percolation process becomes gradual. The temperature dependence of resistivity measurements show that the fluorinated carbon black‐filled PVDF composites exhibit a high PTC intensity and a low NTC effect. These phenomena were discussed in terms of thermodynamic interactions between fluorinated carbon and the PVDF matrix. The dielectric behavior was also investigated in this study. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1063–1070, 2001     

Conductive chitosan/multi walled carbon nanotubes electrospun nanofiber feasibility

The current study focuses on the electrospinning of chitosan (CHT)/multi walled carbon nanotubes (MWNTs) composite nanofiber using a highly stable dispersion. The acetic acid (1–100%) and trifluoroacetic acid/dichloromethane (TFA/DCM 70: 30) was tested as solvent, and the TFA/DCM (70 : 30) is most preferred for fiber formation process with acceptable electrospinnability. Moreover, a new protocol was used to establish proper technique for preparation of electrospinning solution. FT-IR spectroscopy utilized to infer the extent of interaction between CHT polymer chain and MWNT filaments. A quite simple technique was employed to show the stability of electrospinning solution before nanofiber formation process. Scanning electronic microscope (SEM) was employed to show the influence of spinning parameters on surface morphology of electrospun fiber. Under optimized condition, homogeneous and beadfree CHT/MWNTs nanofibers and known physical characteristics were prepared. The formation of conducting nanofibers based on CHT nanocomposites can be considered as a significant improvement in electrospinning of CHT/CNT dispersion. The direct outcome of the current study includes the homogeneous CHT/MWNTs nanofibers with an average diameter of 275 nm and a conductivity of 9×10⁻⁵ S/cm. These results are extremely important for further investigation regarding biomedical applications.     

Preparation and tribological properties of carbon fibre reinforced poly(vinylidene fluoride) composites

Abstract

The current study examines the tribological performance of poly(vinylidene fluoride) (PVDF) and carbon fibre reinforced poly(vinylidene fluoride) (CF/PVDF) under dry sliding condition. Different contents of carbon fibres (CFs) were employed as reinforcement. All filled and unfilled polyimide composites were tested against CGr15 ball and representative testing was performed. The effects of CF content on tribological properties of the composites were investigated. The worn surface morphologies of neat PVDF and its composites were examined by scanning electron microscopy and the wear mechanisms were discussed. Moreover, all filled PVDFs have superior tribological characteristics to unfilled PVDFs. The optimum wear reduction was obtained when the content of CF is 20 vol.-%.     

Synthesize procedures,mechanical and electrical properties of poly(vinylidene fluoride) nanocomposite thin films containing multiwalled carbon nanotubes

A procedure is proposed to prepare poly(vinylidene fluoride) (PVDF) multiwalled carbon nanotubes (MWCNTs) nanocomposite thin films with improved mechanical and dielectric properties compared to the pure PVDF films. The PVDF/MWCNT mixture with a composition range from 0.0 to 5.0% MWCNTs by weight was formed using solution blending and the ultrasonic dispersion method and then spin coated on a rotating glass substrate to produce films nearly 20 μ thick. Results indicate that the appropriate addition of MWCNTs (up to 3.0 wt%) to PVDF can significantly increase its elastic modulus while decrease its fracture toughness. The elastic modulus shows softening at a 5.0 wt% MWCNT loading. The DC and AC conductivity of the composite films were also examined with various MWCNTs concentrations. The dielectric constants were found more than doubled for 0.5 wt% MWCNTs composite compared to the values for the pure PVDF. POLYM. COMPOS., 2012. © 2011 Society of Plastics Engineers     

Polymorphism in intercalated poly(vinylidene fluoride)/clay nanocomposites

Polymorphism in poly(vinylidene fluoride) (PVDF)/clay nanocomposites was studied. Poly(vinylidene fluoride)/clay nanocomposites were prepared with melt intercalation. The samples were characterized with X‐ray diffraction, differential scanning calorimetry, and Fourier transform infrared spectroscopy. The nanocomposite exhibited the β form. Thermal annealing performed at 125 and 185°C showed that the β form of PVDF was stable. The stability of the β form of PVDF was ascertained from these studies. The β form of PVDF in the nanocomposites could be due to crystallization in the constrained phase. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2036–2040, 2003