Fabrication and evaluation of thin layer PVDF composites using MWCNT reinforcement: Mechanical, electrical and enhanced electromagnetic interference shielding properties

Impact of synthesis temperature on morphology, rheology and electromagnetic interference shielding of CVD-grown carbon nanotube/polyvinylidene fluoride nanocomposites

Abstract: Employing chemical vapor deposition technique, multi-walled carbon nanotubes (CNTs) were synthesized over Fe catalyst at a broad range of temperatures, i.e. 550° C to 950° C (at 100° C intervals). CNTs were melt-mixed into a polyvinylidene fluoride (PVDF) matrix at various loadings, and then compression molded. Surprisingly, despite the ascending trend of CNT powder conductivity with the synthesis temperature, the nanocomposites made with CNT synthesized at 650° C had significantly lower percolation threshold (around 0.4 wt%) and higher electromagnetic interference shielding effectiveness (EMI SE) (20.3 dB over the X-band for 3.5 wt% CNT and 1.1 mm thickness) than the other temperatures. Exhaustive characterization studies were conducted on both CNTs and composites to unveil their morphological and electrical characteristics. Superior EMI shielding of CNT 650° C was attributed to a combination of high carbon purity, aspect ratio, crystallinity, and moderate powder conductivity along with decent state of dispersion within the PVDF matrix.

Crystal polymorphism in polydiacetylene-embedded electrospun polyvinylidene fluoride nanofibers.

Abstract: In this study, polydiacetylene (PDA) is embedded in electrospun polyvinylidene fluoride (PVDF) nanofibers for the preparation of mats with dual colorimetric and piezoelectric responses. The diacetylene monomers are self-assembled during the electrospinning process. The PDA-embedded PVDF nanofibers in the blue phase are obtained via photo-polymerization upon UV-light irradiation. The colorimetric transition of the nanofibers is studied as a function of temperature using a spectrophotometer. The morphology and crystal polymorphism of the nanofibers are investigated. The results show that the addition of PDA increases the diameter of the nanofibers due to the increase in the electrospinning solution viscosity. The results of Fourier transform infrared and wide angle X-ray diffraction demonstrate that PDA has the effect of inhibiting the growth of non-polar α-phase crystals, while promoting the growth of the polar β-phase. However, the red phase of PDA-embedded PVDF exhibits a lower intensity of the β-phase in comparison to that of the blue phase. In fact, the blue-to-red color transition of the PDA-embedded electrospun PVDF nanofibers is accompanied by the variation of piezoelectric signaling caused by variations in the β-phase. This phenomenon creates great potential in commercial detection sensors in addition to their colorimetric detection properties.

Lightweight, flexible and thin Fe3O4-loaded, functionalized multi walled carbon nanotube buckypapers for enhanced X-band electromagnetic interference shielding

Abstract: Electromagnetic interference (EMI) is undesirable and uncontrolled interference with the signal of intelligence. This is controlled by using either novel materials, or appropriate electronic design or a combination of both. In this context, functionalized multiwalled carbon nanotubes (FMWCNTs) have been proposed to use as EM shielding materials because of their promising electromagnetic properties, high flexibility, and high electrical conductivity. The non-functionalised MWCNTs does not demonstrate high shielding of electromagnetic waves but with acid functionalisation and further loading with optimized nanoparticles of Fe3O4, enhanced absorption (15.85 dB), enhanced reflection (9.43 dB), resulted in high total specific shielding effectiveness of around 49.56 dB (g cm−3)−1. All samples were light weight, flexible, thin and self-standing in the form of a buckypaper of thickness of 50 µm and density of 0.51 g cm−3. These buckypapers could be promising materials for electromagnetic shielding via both absorption and reflection. A fine amalgamated system of MWCNTs with half metallic Fe3O4, resulting in enhanced conductivity, in an extremely thin and flexible matrix, is considered to be the main contribution to these high shielding effectiveness values.

Fabrication and characterization of polydiacetylene supramolecules in electrospun polyvinylidene fluoride nanofibers with dual colorimetric and piezoelectric responses

Abstract: The ability to prepare Polydiacetylenes based materials in the polyvinylidene fluoride matrix polymer is interesting due to the combination of colorimetric and electrical signaling. The new PVDF/PDA composite nanofibers were prepared via the electrospinning method. The self-assembly of diacetylene monomers (PCDAs) occurred during the electrospinning process. The assembled diacetylene monomers in the PVDF nanofibres were further polymerized to form PDA. Full factorial experimental design was applied to investigate the influence of PVDF concentration and PCDA content on the morphology of nanofibers. The colorimetric transitional of the uniform and beadless PVDF/PDA nanofibers were studied as a function of temperature. The crystal polymorphism of these structures were evaluated using Fourier transform infrared, differential scanning calorimetry, and wide angle X-Ray diffraction. The piezoelectric response of the PVDF/PDA nanofibers in the red and blue phases was also measured. The results showed that a combination of colorimetric and piezoelectric responses is available with composite nanofibers of PVDF/PDA. The polymorphism investigation demonstrated that assembled PCDAs have the effect of inhibiting the growth of non-polar α phase crystals, while promoting the growth of polar β phase. Moreover, the electrospun PVDF/PCDA nanofibers after UV-irradiation and formation of PDA exhibited greater intensity of β-phase in comparison to that before irradiation. However, the red phase of PVDF/PDA nanofibers indicated less fraction of β-phase than the blue phase. The blue-to-red color transition of PVDF/PDA composite nanofibers accompanied by the variation of piezoelectric response could open new avenues for many sensor applications.

Development of polyvinylidene fluoride-graphite composites as an alternate material for electromagnetic shielding applications

Abstract: Polyvinylidene fluoride (PVDF)-graphite composites have been developed using solution mixing with uniform dispersion of micro-fillers within the PVDF polymer matrix for electromagnetic interference (EMI) shielding applications. A conductive network of flake shaped graphite particles is formed within the PVDF polymer layers which improved the electrical conductivity of the composite thus providing promising EMI shielding properties. Conductivity of the composite increased by several orders of magnitude on graphite (80 wt%) incorporation in the PVDF (i.e. from 3.41 × 10−13 S cm−1 to 120 S cm−1). A high effective dielectric constant ( at a frequency of 8.2 GHz) has also been obtained for the PVDF-graphite composite having 80 wt% graphite. A high absorption dominated total shielding effectiveness value of ~98 dB has also been achieved at a frequency of 8.2 GHz for the above mentioned composite. The results are promising for using the PVDF-graphite composite as EMI shielding material in the X-band frequency.

Graphene/Polymer Nanocomposites

Abstract: Graphene has emerged as a subject of enormous scientific interest due to its exceptional electron transport, mechanical properties, and high surface area. When incorporated appropriately, these atomically thin carbon sheets can significantly improve physical properties of host polymers at extremely small loading. We first review production routes to exfoliated graphite with an emphasis on top-down strategies starting from graphite oxide, including advantages and disadvantages of each method. Then solvent- and melt-based strategies to disperse chemically or thermally reduced graphene oxide in polymers are discussed. Analytical techniques for characterizing particle dimensions, surface characteristics, and dispersion in matrix polymers are also introduced. We summarize electrical, thermal, mechanical, and gas barrier properties of the graphene/polymer nanocomposites. We conclude this review listing current challenges associated with processing and scalability of graphene composites and future perspectives f...

Carbon nanotube–polymer composites: Chemistry, processing, mechanical and electrical properties

Abstract: Carbon nanotubes have long been recognized as the stiffest and strongest man-made material known to date. In addition, their high electrical conductivity has roused interest in the area of electrical appliances and communication related applications. However, due to their miniscule size, the excellent properties of these nanostructures can only be exploited if they are homogeneously embedded into light-weight matrices as those offered by a whole series of engineering polymers. We review the present state of polymer nanocomposites research in which the fillers are carbon nanotubes. In order to enhance their chemical affinity to engineering polymer matrices, chemical modification of the graphitic sidewalls and tips is necessary. In this review, an extended account of the various chemical strategies for grafting polymers onto carbon nanotubes and the manufacturing of carbon nanotube/polymer nanocomposites is given. The mechanical and electrical properties to date of a whole range of nanocomposites of various carbon nanotube contents are also reviewed in an attempt to facilitate progress in this emerging area.

Dispersion and functionalization of carbon nanotubes for polymer-based nanocomposites: a review

Abstract: Carbon nanotubes (CNTs) hold the promise of delivering exceptional mechanical properties and multi-functional characteristics. Ever-increasing interest in applying CNTs in many different fields has led to continued efforts to develop dispersion and functionalization techniques. To employ CNTs as effective reinforcement in polymer nanocomposites, proper dispersion and appropriate interfacial adhesion between the CNTs and polymer matrix have to be guaranteed. This paper reviews the current understanding of CNTs and CNT/polymer nanocomposites with two particular topics: (i) the principles and techniques for CNT dispersion and functionalization and (ii) the effects of CNT dispersion and functionalization on the properties of CNT/polymer nanocomposites. The fabrication techniques and potential applications of CNT/polymer nanocomposites are also highlighted.

Highly aligned graphene/polymer nanocomposites with excellent dielectric properties for high-performance electromagnetic interference shielding.

Abstract: Nanocomposites that contain reinforcements with preferred orientation have attracted significant attention because of their promising applications in a wide range of multifunctional fields. Many efforts have recently been focused on developing facile methods for preparing aligned graphene sheets in solvents and polymers because of their fascinating properties including liquid crystallinity and highly anisotropic characteristics. Self-aligned in situ reduced graphene oxide (rGO)/polymer nanocomposites are prepared using an all aqueous casting method. A remarkably low percolation threshold of 0.12 vol% is achieved in the rGO/epoxy system owing to the uniformly dispersed, monolayer graphene sheets with extremely high aspect ratios (>30000). The self-alignment into a layered structure at above a critical filler content induces a unique anisotropy in electrical and mechanical properties due to the preferential formation of conductive and reinforcing networks along the alignment direction. Accompanied by the anisotropic electrical conductivities are exceptionally high dielectric constants of over 14000 with 3 wt% of rGO at 1 kHz due to the charge accumulation at the highly-aligned conductive filler/insulating polymer interface according to the Maxwell-Wagner-Sillars polarization principle. The highly dielectric rGO/epoxy nanocomposites with the engineered structure and properties present high performance electromagnetic interference shielding with a remarkable shilding efficiency of 38 dB.

Formation of percolating networks in multi-wall carbon-nanotube–epoxy composites

Abstract: This paper explores the use of aligned chemical vapour deposition (CVD)-grown multi-wall carbon nanotubes as a conductive filler in an epoxy system based on a bisphenol-A resin and an amine hardener. During the production of composite samples containing 0.01 wt% nanotubes, stirring rates, resin temperatures, and curing temperatures were varied. Optical microscopy of bulk samples was used to classify the degree of nanotube agglomeration. In addition, the specific bulk conductivity of the materials was analysed by AC impedance spectroscopy. The resulting electrical properties of the composites ranged from purely dielectric behaviour to bulk conductivities of 10−3 Sm−1 and were found to depend strongly on three separate stages during processing. All samples contained individually dispersed carbon nanotubes after initial shear-intensive stirring. Negative surface charges on the nanotubes led to charge-stabilised dispersions. After the addition of the hardener, the nanotubes reaggregated upon application of elevated temperatures and/or modest shear forces. The formation of the final network depended on the curing temperature of the matrix. The experimental results are compared to previous studies on nanotube and carbon black epoxy composites and are discussed with respect to aspects of colloid theory.