Well-dispersed single phasic flower-like zero valent iron nanoparticles have been synthesized und... more Well-dispersed single phasic flower-like zero valent iron nanoparticles have been synthesized under aer-obic conditions using a facile approach without the addition of any additives or templates. The role of hydroxyl groups of polyhydroxy alcohols in controlling surface morphology of nanoparticles has been thoroughly investigated. The obtained nanoparticles have been characterized by TEM, FE-SEM, XRD and BET surface area analyzer. Electron microscopy analyses reveal that the solvent plays a pivotal role in determining the morphology of the particles. With increase in viscosity of the solvent, formations of 'petal-like' structures, which are joined at the center are formed. The nitrate removal efficiency of the iron nanoparticles synthesized in different solvents has been studied and it is seen that the ''flower-like " iron nanoparticles were most active in the removal of nitrate. Experiments have been done by varying (i) nitrate concentrations, (ii) nanoparticle dose, and (iii) type of nanoparticles. The results conclude that highest removal efficiency ($100%) was achieved when the nanoparticle dose was 2.88 g/L, even for high nitrate concentrations up to 400 mg/L. The major highlight of this work is the fact that even though the nanoparticles synthesized in glycerol-water mixture have larger size in comparison to the other nanopar-ticles, still they remove the nitrates with highest efficiency. "
There is an enormous scope for graphene and its analogues in electromagnetic interference (EMI) a... more There is an enormous scope for graphene and its analogues in electromagnetic interference (EMI) applications, especially as microwave absorbers. Recent studies have shown that graphene analogues exhibit excellent electromagnetic shielding through uniquely designed 3D macroporous foams or as ultrathin papers and thus, are inevitable towards developing hybrid architectures. Herein, we provide a comprehensive evaluation of the key structural and mechanistic attributes of both graphene-based foams and papers towards EM shielding applications. Furthermore, we emphasize on the crucial aspect of architecture and alignment of graphene in both foam and paper towards enhancing EMI shielding for emerging applications.
Unique multilayered assembly was designed here using polymeric blends containing " flower-like " ... more Unique multilayered assembly was designed here using polymeric blends containing " flower-like " ferrite nanoparticles conjugated with multiwall carbon nanotubes (MWCNTs) for attenuating 99.999% of the incoming electromagnetic (EM) radiation. In comparison to a traditional single layered structure, this unique assembly is superior for myriad applications related to suppressing the incoming EM radiation, mostly by absorption. The three key requirementsimpedance wave matching, absorption, and multiple scattering from the heterogeneous structureswere accounted here by suitably modifying the nanomaterials. A bicomponent blend consisting of two immiscible polymers, poly-vinylidine fluoride (PVDF) and polycarbonate (PC), was used here to construct the multilayered assembly wherein selective localization of nanoparticles in one of the components, driven by thermodynamics, reduced the percolation threshold of the nanoparticles. In order to improve the impedance matching, MWCNTs were functionalized using the defect sites induced by harsh chemical treatment and incorporated in PC/PVDF blends as the inner layer of the multilayered assembly. The conjugation of flower-like Fe 3 O 4 nanoclusters on the defect sites of the surface functionalized MWCNTs absorbs the incident EM waves due to the interfacial polarization of different heterogeneous structures. The value of total loss tangent, attenuation constant, and absorption coefficient supports absorption driven shielding in PC/PVDF blends. The efficient thermal dissipation together with high absorption led to fix this as the intermediate layer of the assembly. Finally, multiple scattering through the network of pristine MWCNTs was utilized as the outermost layer of the assembly, which guided the penetrated waves to interact with this layer resulting in maximum attenuation. This unique three-layered assembly, which exhibited a shielding effectiveness of −64 dB at 18 GHz for 0.9 mm thickness, powered by multifunctionality, offer amendable replacement of the existing solution related to EM absorption.
Conducting polymer composites containing ferromagnetic grafted-graphene derivatives are already a... more Conducting polymer composites containing ferromagnetic grafted-graphene derivatives are already appreciated for their lightweight, flexibility, and cost effectiveness in terms of microwave absorption. To further leverage the said properties of this wonder material, we propose a highly efficient replacement by blending conducting multiwall carbon nanotube (MWCNT) and FeCo anchored covalent cross-linked reduced graphene oxide (rGO) with poly(vinylidene fluoride) (PVDF). Interconnected conducting network of MWCNTs introduces higher electrical conductivity in the blend which is essential for microwave absorption. FeCo-anchored porous interconnected rGO framework was designed via solvent-mediated in situ coreduction in the presence of Fe(II) and Co(II) precursors. Resulting cross-linked-rGO/FeCo displays fascinating coexistence of ferromagnet-ism and conducting-dielectric behavior, while largely preserving the robust 3D porous interconnected structure. Coupled with conducting MWCNTs, diamine cross-linked rGO/FeCo in a soft polymer matrix yields remarkably high total shielding effectiveness (SE T) of −41.2 dB at 12 GHz, for a meager 10 wt % filler content. In addition, the composite materials display efficient heat dissipation abilities in conjunction with the trend in their thermal conductivities. This new-age microwave-absorbing material, powered by multifunctionality and tunable magnetodielectric properties, henceforth offers an amendable, cost-effective replacement to the existing solutions.
Fabrication of multilayered thin polymer films by rational arrangement of tailor-made nanocomposi... more Fabrication of multilayered thin polymer films by rational arrangement of tailor-made nanocomposites was designed to absorb electromagnetic (EM) radiation. Mn (manganese) ferrite nanoparticles were incorporated in polyvinylidene fluoride (PVDF) matrix, along with conductive MWCNTs, treated as outer layers of the multilayer assembly. The higher permittivity, permeability and attenuation constant ensure the higher absorption ability of these resulting outer layers. Selectively etching of one of the phases of the inner layers, which consist of immiscible blends of polycarbonate (PC) and PVDF with conductive MWCNTs, porous structure can be designed to maximize the penetration of incoming EM radiation from outer layers. Further scattering of the penetrated EM wave between the interfacial walls of conducting nano fillers inside the porous matrix enhance the shielding efficiency. The resulting ultrathin (0.60 mm) multilayered architecture was able to block > 99.999 % (ca. À50dB) of the incoming EM radiation. This new-age EM radiation absorbing material, powered by multi-functionality henceforth, offers amendable, cost-effective replacement to the existing solutions.
The fabrication of thin multilayer polymer nanocomposite films and their judicious arrangement in... more The fabrication of thin multilayer polymer nanocomposite films and their judicious arrangement in a sandwich structure to attenuate incoming electromagnetic (EM) radiation, mostly by absorption, is discussed herein. Two key properties (reasonably high conductivity, with high dielectric loss and magnetic permeability) were targeted here by using multiwall nanotubes (MWCNTs) and BaTiO 3 /Fe 3 O 4 (BT/Fe) co-doped graphene oxide (GO) sheets to design soft functional nanocomposites using bi-component blends of PC (polycarbonate) and PVDF (polyvinylidene fluoride). High dielectric loss and magnetic permeability were achieved by uniformly distributing BT and Fe nanoparticles on the huge specific surface area provided by the GO sheets. The MWCNTs were non-covalently modified to exfoliate the nanotubes and to get a well-connected structure of the blend components. The MWCNTs were thoroughly characterized by TEM, UV-vis, fluorescence emission, Raman and TGA. This surface modification of the MWCNTs also helps with their specific localization in the continuous bi-component blends. BT and Fe were co-doped onto the GO sheets by a well-designed step-by-step synthesis protocol, and the product can facilitate the absorption of incoming EM radiation. This hybrid structure was thoroughly characterized by various microscopic and spectroscopic techniques. By following a sequential mixing protocol, the BT/Fe co-doped GO sheets can be specifically localized in the PC components of the blends while the MWCNTs localize in the PVDF phase through a process driven by thermodynamics. This provides excellent heterogeneous boundaries with multiple scattering within the engineered nanostructures, in addition to retaining the conducting network and the associated dielectric loss properties. The resultant local field variation of such boundaries and the presence of highly lossy materials readily enhance the EM attenuation coefficient. The bulk compositions exhibited a high shielding effectiveness (SE) of À35 dB at 18 GHz (>85% absorption), and when rationally stacked into a multilayer architecture with absorption–multiple reflection–absorption pathways, the SE was further enhanced to À46 dB for a thin shield of 0.9 mm thickness. Such a high SE indicates >99.99% attenuation of the incoming EM radiation. This new-generation EM suppressor, distinguished by its multifunctionality and tunable dielectric and magnetic properties, hence offers an amendable, cost-effective replacement to existing solutions.
A novel fluorophore–spacer–receptor has been designed with hydrazono methyl phenol as the recepto... more A novel fluorophore–spacer–receptor has been designed with hydrazono methyl phenol as the receptor, anthracene as the fluorophore and imine (CQN) groups as the spacer. This newly designed fluorophoric system has a receptor that can bind with ferrites and a fluorophore core that can conjugate non-covalently with multiwalled carbon nanotubes (MWNTs) via p–p conjugation. The hybrid nanoparticles were thoroughly characterized using Raman, UV-vis and fluorescence spectroscopy. This unique hybrid is further explored as a novel material to screen electromagnetic (EM) radiation. By precisely localizing these hybrids in a given phase of an immiscible co-continuous blend, unique microstructures can be constructed. Herein, blends of polyvinylidene fluoride (PVDF) and polycarbonate (PC) were chosen as a model system. The hybrid nanoparticles were selectively localized in the PVDF phase owing to its higher polarity and were systematically characterized by electron microscopic and solution–dissolution techniques. The hybrid nanoparticles that were designed to shield from the incident EM radiation resulted in 499.99% attenuation, dominated mostly by absorption. This non-covalent approach of conjugating MWNTs with ferrites, aided by the fluorophoric system, was noted to be a more effective way to improve the properties (both bulk electrical conductivity and structural) than direct physical mixing/covalent conjugation approaches. In order to further enhance the shielding effectiveness (SE), a layer-by-layer architecture was constructed essentially with outer layers containing PC/PVDF blends with a MWNT–ferrite hybrid and the inner layers consisting of PC/PVDF blends with only MWNTs. An ultra-thin shield of 0.90 mm showed 499.9999% attenuation suggesting new pathways for designing lightweight, flexible EMI shielding materials.
To minimize electromagnetic (EM) pollution, two key parameters, namely, intrinsic wave impedance ... more To minimize electromagnetic (EM) pollution, two key parameters, namely, intrinsic wave impedance matching and intense absorption of incoming EM radiation, must satisfy the utmost requirements. To target these requirements, soft conducting composites consisting of binary blends of polycarbonate (PC) and poly(vinylidene fluoride) (PVDF) were designed with doped multiwalled carbon nanotubes (MWCNTs) and a three-dimensional cross-linked graphene oxide (GO) framework doped with ferrite nanoparticles. The doping of α-MnO 2 onto the MWCNTs ensured intrinsic wave impedance matching in addition to providing conducting pathways, and the ferrite-doped cross-linked GO facilitated the enhanced attenuation of the incoming EM radiation. This unique combination of magnetodielectric coupling led to a very high electromagnetic shielding efficiency (SE) of −37 dB at 18 GHz, dominated by absorption-driven shielding. The promising results from the composites further motivated us to rationally stack individual composites into a multilayer architecture following an absorption−multiple reflection−absorption pathway. This resulted in an impressive SE of −57 dB for a thin shield of 0.9-mm thickness. Such a high SE indicates >99.999% attenuation of the incoming EM radiation, which, together with the improvement in structural properties, validates the potential of these materials in terms of applications in cost-effective and tunable solutions.
Herein, we demonstrate that very high electromagnetic (EM) shielding efficiency can be achieved b... more Herein, we demonstrate that very high electromagnetic (EM) shielding efficiency can be achieved by dispersing nanoengineered FeCo anisometric nanostructures in a poly(vinylidene difluoride) matrix in the presence of conductive nanofillers (multiwall carbon nanotubes, MWCNTs). The FeCo nanorods (∼800 nm) and nanocubes (∼100 nm) were fabricated by a facile surfactant and polymer-assisted one-pot borohydride reduction method. The growth mechanism depicted a two-directional growth for cubes, whereas for nanorods, a unidirectional growth pattern across the (110) plane was evident. A total shielding effectiveness (SE T) of −44 dB at 18 GHz was achieved for a particular combination of FeCo nanorods and MWCNT, and for nanocube-based composites, it was found to be −39 dB at 18 GHz. It was observed from zero field cooled-field cooled curves that the samples displayed room temperature ferromagnetism. An excellent correlation between high aspect ratio FeCo nanorod and superior EM absorption (89%) was explored, pertaining to the fact that nanorods possessed higher magnetic saturation (177.1 emu/g) and coercivity (550 Oe) in contrast to the nanocubes with similar composition. Furthermore, theoretical insight into the mechanism revealed a high degree of interface scattering between conductive MWCNT and magnetic loss components, giving rise to an excellent synergy between magnetic and dielectric parts.
The fabrication of thin multilayer polymer nanocomposite films and their judicious arrangement in... more The fabrication of thin multilayer polymer nanocomposite films and their judicious arrangement in a sandwich structure to attenuate incoming electromagnetic (EM) radiation, mostly by absorption, is discussed herein. Two key properties (reasonably high conductivity, with high dielectric loss and magnetic permeability) were targeted here by using multiwall nanotubes (MWCNTs) and BaTiO 3 /Fe 3 O 4 (BT/Fe) co-doped graphene oxide (GO) sheets to design soft functional nanocomposites using bi-component blends of PC (polycarbonate) and PVDF (polyvinylidene fluoride). High dielectric loss and magnetic permeability were achieved by uniformly distributing BT and Fe nanoparticles on the huge specific surface area provided by the GO sheets. The MWCNTs were non-covalently modified to exfoliate the nanotubes and to get a well-connected structure of the blend components. The MWCNTs were thoroughly characterized by TEM, UV-vis, fluorescence emission, Raman and TGA. This surface modification of the MWCNTs also helps with their specific localization in the continuous bi-component blends. BT and Fe were co-doped onto the GO sheets by a well-designed step-by-step synthesis protocol, and the product can facilitate the absorption of incoming EM radiation. This hybrid structure was thoroughly characterized by various microscopic and spectroscopic techniques. By following a sequential mixing protocol, the BT/Fe co-doped GO sheets can be specifically localized in the PC components of the blends while the MWCNTs localize in the PVDF phase through a process driven by thermodynamics. This provides excellent heterogeneous boundaries with multiple scattering within the engineered nanostructures, in addition to retaining the conducting network and the associated dielectric loss properties. The resultant local field variation of such boundaries and the presence of highly lossy materials readily enhance the EM attenuation coefficient. The bulk compositions exhibited a high shielding effectiveness (SE) of À35 dB at 18 GHz (>85% absorption), and when rationally stacked into a multilayer architecture with absorption–multiple reflection–absorption pathways, the SE was further enhanced to À46 dB for a thin shield of 0.9 mm thickness. Such a high SE indicates >99.99% attenuation of the incoming EM radiation. This new-generation EM suppressor, distinguished by its multifunctionality and tunable dielectric and magnetic properties, hence offers an amendable, cost-effective replacement to existing solutions.
The world has dominated by automation, wireless communication and various electronic equipments, ... more The world has dominated by automation, wireless communication and various electronic equipments, which has led to the most undesirable offshoots like electromagnetic (EM) pollution. The rationale is environmental concern and the necessity to develop EM absorbing materials. This paper reviews the state of the art of designing polymer based nanocomposites containing nanoscopic particles with high electrical conductivity and complex microwave properties for enhanced EM attenuation. Given the brevity of this review article, herein we have summarized the high frequency millimetre wave absorbing properties of polymer nanocomposites consisting of various nanoparticles that either reflect or absorb microwave radiation like electrically conducting carbon nanotubes (CNTs) and graphene nanosheets (GNs), high dielectric constant ceramic nanoparticles that show relaxation loss in the microwave frequency and magnetic metal and ferrite nanoparticles that absorb microwave radiation through natural resonance, eddy current and hysteresis losses. Furthermore, we have stressed the necessity and impact of hybrid nanoparticles consisting of magnetic and dielectric nanoparticles along with conducting inclusions like CNT and GNs in this review. Electromagnetic interference (EMI) theory and necessary criterion for attenuation has been briefly discussed. The emphasis is made on various mechanisms towards EM attenuation controlled by these nanoparticles. Various structures developed using polymer nano-composites like bulk, foam and layered structures and their effect on EM attenuation has been elaborately discussed. In addition, various covalent/non-covalent modifications on nanoparticles have been juxtaposed in context to EM attenuation. In addition, we have highlighted important facets and direction for enhancing the microwave attenuation.
Nanoscale ordering in a polymer blend structure is indispensable to obtain materials with tailore... more Nanoscale ordering in a polymer blend structure is indispensable to obtain materials with tailored properties. It was established here that controlling the arrangement of nanoparticles, with different characteristics, in co-continuous PC/PVDF (polycarbonate/poly(vinylidene fluoride)) blends can result in outstanding microwave absorption (ca. 90%). An excellent reflection loss (R L) of ca. À71 dB was obtained for a model blend structure wherein the conducting (multiwall carbon nanotubes, MWNTs) and the magnetic inclusions (Fe 3 O 4) are localized in PVDF and the dielectric inclusion (barium titanate, BT) is in PC. The MWNTs were modified using polyaniline, which facilitates better charge transport in the blends. Furthermore, by introducing surface active groups on BT nanoparticles and changing the macroscopic processing conditions , the localization of BT nanoparticles can be tailored, otherwise BT nanoparticles would localize in the preferred phase (PVDF). In this study, we have shown that by ordered arrangement of nanoparticles, the incoming EM radiation can be attenuated. For instance, when PANI–MWNTs were localized in PVDF, the shielding was mainly through reflection. Now by localizing the conducting inclusion and the magnetic lossy materials in PVDF and the dielectric materials in PC, an outstanding shielding effectiveness of ca. À37 dB was achieved where shielding was mainly through absorption (ca. 90%). Thus, this study clearly demonstrates that lightweight microwave absorbers can be designed using polymer blends as a tool.
A unique approach was adopted to drive the multiwall carbon nanotubes (MWNTs) to the interface of... more A unique approach was adopted to drive the multiwall carbon nanotubes (MWNTs) to the interface of immiscible PVDF–ABS blends by wrapping the nanotubes with a mutually miscible homopolymer (PMMA). A tailor made interface with an improved stress transfer was achieved in the blends with PMMA wrapped MWNTs. This manifested in an impressive 108% increment in the tensile strength and 48% increment in the Young's modulus with 3 wt% PMMA wrapped MWNTs in striking contrast to the neat blends. As the PMMA wrapped MWNTs localized at the interface of PVDF–ABS blends, the electrical conductivity could be tuned with respect to only MWNTs, which were selectively localized in the PVDF phase, driven by thermodynamics. The electromagnetic shielding properties were assessed using a vector network analyser in a broad range of frequency, X-band (8–12 GHz) and K u-band (12–18 GHz). Interestingly, enhanced EM shielding was achieved by this unique approach. The blends with only MWNTs shielded the EM waves mostly by reflection however, the blends with PMMA wrapped MWNTs (3 wt%) shielded mostly by absorption (62%). This study opens new avenues in designing materials, which show simultaneous improvement in mechanical, electrical conductivity and EM shielding properties.
A unique strategy was adopted here to improve the compatibility between the components of an immi... more A unique strategy was adopted here to improve the compatibility between the components of an immiscible polymer blend and strengthen the interface. PMMA, a mutually miscible polymer to both PVDF and ABS, improved the compatibility between the phases by localizing at the blends interface. This was supported by the core–shell formation with PMMA as the shell and ABS as the core as observed from the SEM micrographs. This phenomenon was strongly contingent on the concentration of PMMA in the blends. This strategy was further extended to localize graphene oxide (GO) sheets at the blends interface by chemically coupling it to PMMA (PMMA-g-GO). A dramatic increment of ca. 84% in the Young's modulus and ca. 124% in the yield strength was observed in the presence of PMMA-g-GO with respect to the neat blends. A simultaneous increment in both the strength and the modulus was observed in the presence of PMMA-g-GO whereas, only addition of GO resulted in a moderate improvement in the yield strength. This study reveals that a mutually miscible polymer can render compatibility between the immiscible pair and can improve the stress transfer at the interface.
In order to obtain better materials, control over the precise location of nanoparticles is indisp... more In order to obtain better materials, control over the precise location of nanoparticles is indispensable. It is shown here that ordered arrangements of nanoparticles, possessing different characteristics (electrical/ magnetic dipoles), in the blend structure can result in excellent microwave absorption. This is manifested from a high reflection loss of ca. −67 dB for the best blend structure designed here. To attenuate electromagnetic radiation, the key parameters of high electrical conductivity and large dielectric/magnetic loss are targeted here by including a conductive material [multiwall carbon nanotubes, MWNTs], ferroelectric nanostructured material with associated relaxations in the GHz frequency [barium titanate, BT] and lossy ferromagnetic nanoparticles [nickel ferrite, NF]. In this study, bi-continuous structures were designed using 50/50 (by wt) blends of polycarbonate (PC) and polyvinylidene fluoride (PVDF). The MWNTs were modified using an electron acceptor molecule, a derivative of perylenediimide, which facilitates π–π stacking with the nanotubes and stimulates efficient charge transport in the blends. The nanoscopic materials have specific affinity towards the PVDF phase. Hence, by introducing surface-active groups, an ordered arrangement can be tailored. To accomplish this, both BT and NF were first hydroxylated followed by the introduction of amine-terminal groups on the surface. The latter facilitated nucleophilic substitution reactions with PC and resulted in their precise location. In this study, we have shown for the first time that by a compartmentalized approach, superior EM attenuation can be achieved. For instance, when the nanoparticles were localized exclusively in the PVDF phase or in both the phases, the minimum reflection losses were ca. −18 dB (for the MWNT/BT mixture) and −29 dB (for the MWNT/NF mixture), and the shielding occurred primarily through reflection. Interestingly, by adopting the compartmentalized approach wherein the lossy materials were in the PC phase and the conductive materials (MWNT) were in the PVDF phase, outstanding reflection losses of ca. −57 dB (for the BT and MWNT combination) and −67 dB (for the NF and MWNT combination) were noted and the shielding occurred primarily through absorption. Thus, the approach demonstrates that nanoscopic structuring in the blends can be achieved under macroscopic processing conditions and this strategy can further be explored to design microwave absorbers.
Multiwall carbon nanotubes (MWNTs) were anchored onto graphene oxide sheets (GOs) via diazonium a... more Multiwall carbon nanotubes (MWNTs) were anchored onto graphene oxide sheets (GOs) via diazonium and C–C coupling reactions and characterized by spectroscopic and electron microscopic techniques. The thus synthesized MWNT–GO hybrid was then melt mixed with 50/50 polyamide6– maleic anhydride-modified acrylonitrile-butadiene-styrene (PA6–mABS) blend to design materials with high dielectric constant (3 0) and low dielectric loss. The phase morphology was studied by SEM and it was observed that the MWNT–GO hybrid was selectively localized in the PA6 phase of the blend. The 3 0 scales with the concentration of MWNT–GO in the blends, which interestingly showed a very low dielectric loss (<0.2) making them potential candidate for capacitors. In addition, the dynamic storage modulus scales with the fraction of MWNT–GO in the blends, demonstrating their reinforcing capability as well.
Herein, we report tailor-made properties by dispersing nanostructured materials in a co-continuou... more Herein, we report tailor-made properties by dispersing nanostructured materials in a co-continuous polymer blend (PVDF/ABS) that is capable of shielding electromagnetic (EM) radiation. To accomplish this, lossy materials were employed like multi-walled carbon nanotubes (MWNTs), and barium titanate (BT), (which exhibit relaxation losses in the microwave frequency domain) and ferrites (like Fe 3 O 4 ). To improve the state of dispersion, the MWNTs were non-covalently modified using 3,4,9,10-perylenetetracarboxylic dianhydride (PTCD) via π-π stacking, and for effective shielding the MWNTs were conjugated with either BT or Fe 3 O 4 nanoparticles through suitable modifications. The hybrid nanoparticles were selectively localized in the PVDF phase, governed by its polarity, and exhibited excellent microwave attenuation. In order to gain insight into the dielectric and magnetic attributes, the microwave parameters were assessed systematically. Taken together, our results uncover polymer blend as a promising candidate for designing lightweight, thermally stable microwave absorber materials.
Lightweight and flexible electromagnetic shielding materials were designed by selectively localiz... more Lightweight and flexible electromagnetic shielding materials were designed by selectively localizing multiwall carbon nanotubes (MWNTs) anchored magnetic nanoparticles in melt mixed co-continuous blends of polyvinylidene fluoride (PVDF) and poly(styrene-co-acrylonitrile) (SAN). In order to facilitate better dispersion, the MWNTs were modified using pyrenebutyric acid (PBA) via p–p stacking. While one of the two-targeted properties, i.e., high electrical conductivity, was achieved by PBA modified MWNTs, high magnetic loss was accomplished by introducing nickel (NF) or cobalt ferrites (CF). Moreover, the attenuation by absorption can be tuned either by using NF (58% absorption) or CF (64% absorption) in combination with PBA-MWNTs. More interestingly, when CF was anchored on to MWNTs via the pyrene derivative, the minimum reflection loss attained was À55 dB in the Ku band (12–18 GHz) frequency and with a large bandwidth. In addition, the EM waves were blocked mostly by absorption (70%). This study opens new avenues in designing flexible and lightweight microwave absorbers.
Highly conducting composites were derived by selectively localizing multiwall carbon nanotubes (M... more Highly conducting composites were derived by selectively localizing multiwall carbon nanotubes (MWNTs) in co-continuous PVDF/ABS (50/50, wt/wt) blends. The electrical percolation threshold was obtained between 0.5 and 1 wt% MWNTs as manifested by a dramatic increase in the electrical conductivity by about six orders of magnitude with respect to the neat blends. In order to further enhance the electrical conductivity of the blends, the MWNTs were modified with amine terminated ionic liquid (IL), which, besides enhancing the interfacial interaction with PVDF, facilitated the formation of a network like structure of MWNTs. This high electrical conductivity of the blends, at a relatively low fraction (1 wt%), was further explored to design materials that can attenuate electromagnetic (EM) radiation. More specifically, to attenuate the EM radiation by absorption, a ferroelectric phase was introduced. To accomplish this, barium titanate (BT) nanoparticles chemically stitched onto graphene oxide (GO) sheets were synthesized and mixed along with MWNTs in the blends. Intriguingly, the total EM shielding effectiveness (SE) was enhanced by ca. 10 dB with respect to the blends with only MWNTs. In addition, the effect of introducing a ferromagnetic phase (Fe 3 O 4) along with IL modified MWNTs was also investigated. This study opens new avenues in designing materials that can attenuate EM radiation by selecting either a ferroelectric (BT–GO) or a ferromagnetic phase (Fe 3 O 4) along with intrinsically conducting nanoparticles (MWNTs).
Well-dispersed single phasic flower-like zero valent iron nanoparticles have been synthesized und... more Well-dispersed single phasic flower-like zero valent iron nanoparticles have been synthesized under aer-obic conditions using a facile approach without the addition of any additives or templates. The role of hydroxyl groups of polyhydroxy alcohols in controlling surface morphology of nanoparticles has been thoroughly investigated. The obtained nanoparticles have been characterized by TEM, FE-SEM, XRD and BET surface area analyzer. Electron microscopy analyses reveal that the solvent plays a pivotal role in determining the morphology of the particles. With increase in viscosity of the solvent, formations of 'petal-like' structures, which are joined at the center are formed. The nitrate removal efficiency of the iron nanoparticles synthesized in different solvents has been studied and it is seen that the ''flower-like " iron nanoparticles were most active in the removal of nitrate. Experiments have been done by varying (i) nitrate concentrations, (ii) nanoparticle dose, and (iii) type of nanoparticles. The results conclude that highest removal efficiency ($100%) was achieved when the nanoparticle dose was 2.88 g/L, even for high nitrate concentrations up to 400 mg/L. The major highlight of this work is the fact that even though the nanoparticles synthesized in glycerol-water mixture have larger size in comparison to the other nanopar-ticles, still they remove the nitrates with highest efficiency. "
There is an enormous scope for graphene and its analogues in electromagnetic interference (EMI) a... more There is an enormous scope for graphene and its analogues in electromagnetic interference (EMI) applications, especially as microwave absorbers. Recent studies have shown that graphene analogues exhibit excellent electromagnetic shielding through uniquely designed 3D macroporous foams or as ultrathin papers and thus, are inevitable towards developing hybrid architectures. Herein, we provide a comprehensive evaluation of the key structural and mechanistic attributes of both graphene-based foams and papers towards EM shielding applications. Furthermore, we emphasize on the crucial aspect of architecture and alignment of graphene in both foam and paper towards enhancing EMI shielding for emerging applications.
Unique multilayered assembly was designed here using polymeric blends containing " flower-like " ... more Unique multilayered assembly was designed here using polymeric blends containing " flower-like " ferrite nanoparticles conjugated with multiwall carbon nanotubes (MWCNTs) for attenuating 99.999% of the incoming electromagnetic (EM) radiation. In comparison to a traditional single layered structure, this unique assembly is superior for myriad applications related to suppressing the incoming EM radiation, mostly by absorption. The three key requirementsimpedance wave matching, absorption, and multiple scattering from the heterogeneous structureswere accounted here by suitably modifying the nanomaterials. A bicomponent blend consisting of two immiscible polymers, poly-vinylidine fluoride (PVDF) and polycarbonate (PC), was used here to construct the multilayered assembly wherein selective localization of nanoparticles in one of the components, driven by thermodynamics, reduced the percolation threshold of the nanoparticles. In order to improve the impedance matching, MWCNTs were functionalized using the defect sites induced by harsh chemical treatment and incorporated in PC/PVDF blends as the inner layer of the multilayered assembly. The conjugation of flower-like Fe 3 O 4 nanoclusters on the defect sites of the surface functionalized MWCNTs absorbs the incident EM waves due to the interfacial polarization of different heterogeneous structures. The value of total loss tangent, attenuation constant, and absorption coefficient supports absorption driven shielding in PC/PVDF blends. The efficient thermal dissipation together with high absorption led to fix this as the intermediate layer of the assembly. Finally, multiple scattering through the network of pristine MWCNTs was utilized as the outermost layer of the assembly, which guided the penetrated waves to interact with this layer resulting in maximum attenuation. This unique three-layered assembly, which exhibited a shielding effectiveness of −64 dB at 18 GHz for 0.9 mm thickness, powered by multifunctionality, offer amendable replacement of the existing solution related to EM absorption.
Conducting polymer composites containing ferromagnetic grafted-graphene derivatives are already a... more Conducting polymer composites containing ferromagnetic grafted-graphene derivatives are already appreciated for their lightweight, flexibility, and cost effectiveness in terms of microwave absorption. To further leverage the said properties of this wonder material, we propose a highly efficient replacement by blending conducting multiwall carbon nanotube (MWCNT) and FeCo anchored covalent cross-linked reduced graphene oxide (rGO) with poly(vinylidene fluoride) (PVDF). Interconnected conducting network of MWCNTs introduces higher electrical conductivity in the blend which is essential for microwave absorption. FeCo-anchored porous interconnected rGO framework was designed via solvent-mediated in situ coreduction in the presence of Fe(II) and Co(II) precursors. Resulting cross-linked-rGO/FeCo displays fascinating coexistence of ferromagnet-ism and conducting-dielectric behavior, while largely preserving the robust 3D porous interconnected structure. Coupled with conducting MWCNTs, diamine cross-linked rGO/FeCo in a soft polymer matrix yields remarkably high total shielding effectiveness (SE T) of −41.2 dB at 12 GHz, for a meager 10 wt % filler content. In addition, the composite materials display efficient heat dissipation abilities in conjunction with the trend in their thermal conductivities. This new-age microwave-absorbing material, powered by multifunctionality and tunable magnetodielectric properties, henceforth offers an amendable, cost-effective replacement to the existing solutions.
Fabrication of multilayered thin polymer films by rational arrangement of tailor-made nanocomposi... more Fabrication of multilayered thin polymer films by rational arrangement of tailor-made nanocomposites was designed to absorb electromagnetic (EM) radiation. Mn (manganese) ferrite nanoparticles were incorporated in polyvinylidene fluoride (PVDF) matrix, along with conductive MWCNTs, treated as outer layers of the multilayer assembly. The higher permittivity, permeability and attenuation constant ensure the higher absorption ability of these resulting outer layers. Selectively etching of one of the phases of the inner layers, which consist of immiscible blends of polycarbonate (PC) and PVDF with conductive MWCNTs, porous structure can be designed to maximize the penetration of incoming EM radiation from outer layers. Further scattering of the penetrated EM wave between the interfacial walls of conducting nano fillers inside the porous matrix enhance the shielding efficiency. The resulting ultrathin (0.60 mm) multilayered architecture was able to block > 99.999 % (ca. À50dB) of the incoming EM radiation. This new-age EM radiation absorbing material, powered by multi-functionality henceforth, offers amendable, cost-effective replacement to the existing solutions.
The fabrication of thin multilayer polymer nanocomposite films and their judicious arrangement in... more The fabrication of thin multilayer polymer nanocomposite films and their judicious arrangement in a sandwich structure to attenuate incoming electromagnetic (EM) radiation, mostly by absorption, is discussed herein. Two key properties (reasonably high conductivity, with high dielectric loss and magnetic permeability) were targeted here by using multiwall nanotubes (MWCNTs) and BaTiO 3 /Fe 3 O 4 (BT/Fe) co-doped graphene oxide (GO) sheets to design soft functional nanocomposites using bi-component blends of PC (polycarbonate) and PVDF (polyvinylidene fluoride). High dielectric loss and magnetic permeability were achieved by uniformly distributing BT and Fe nanoparticles on the huge specific surface area provided by the GO sheets. The MWCNTs were non-covalently modified to exfoliate the nanotubes and to get a well-connected structure of the blend components. The MWCNTs were thoroughly characterized by TEM, UV-vis, fluorescence emission, Raman and TGA. This surface modification of the MWCNTs also helps with their specific localization in the continuous bi-component blends. BT and Fe were co-doped onto the GO sheets by a well-designed step-by-step synthesis protocol, and the product can facilitate the absorption of incoming EM radiation. This hybrid structure was thoroughly characterized by various microscopic and spectroscopic techniques. By following a sequential mixing protocol, the BT/Fe co-doped GO sheets can be specifically localized in the PC components of the blends while the MWCNTs localize in the PVDF phase through a process driven by thermodynamics. This provides excellent heterogeneous boundaries with multiple scattering within the engineered nanostructures, in addition to retaining the conducting network and the associated dielectric loss properties. The resultant local field variation of such boundaries and the presence of highly lossy materials readily enhance the EM attenuation coefficient. The bulk compositions exhibited a high shielding effectiveness (SE) of À35 dB at 18 GHz (>85% absorption), and when rationally stacked into a multilayer architecture with absorption–multiple reflection–absorption pathways, the SE was further enhanced to À46 dB for a thin shield of 0.9 mm thickness. Such a high SE indicates >99.99% attenuation of the incoming EM radiation. This new-generation EM suppressor, distinguished by its multifunctionality and tunable dielectric and magnetic properties, hence offers an amendable, cost-effective replacement to existing solutions.
A novel fluorophore–spacer–receptor has been designed with hydrazono methyl phenol as the recepto... more A novel fluorophore–spacer–receptor has been designed with hydrazono methyl phenol as the receptor, anthracene as the fluorophore and imine (CQN) groups as the spacer. This newly designed fluorophoric system has a receptor that can bind with ferrites and a fluorophore core that can conjugate non-covalently with multiwalled carbon nanotubes (MWNTs) via p–p conjugation. The hybrid nanoparticles were thoroughly characterized using Raman, UV-vis and fluorescence spectroscopy. This unique hybrid is further explored as a novel material to screen electromagnetic (EM) radiation. By precisely localizing these hybrids in a given phase of an immiscible co-continuous blend, unique microstructures can be constructed. Herein, blends of polyvinylidene fluoride (PVDF) and polycarbonate (PC) were chosen as a model system. The hybrid nanoparticles were selectively localized in the PVDF phase owing to its higher polarity and were systematically characterized by electron microscopic and solution–dissolution techniques. The hybrid nanoparticles that were designed to shield from the incident EM radiation resulted in 499.99% attenuation, dominated mostly by absorption. This non-covalent approach of conjugating MWNTs with ferrites, aided by the fluorophoric system, was noted to be a more effective way to improve the properties (both bulk electrical conductivity and structural) than direct physical mixing/covalent conjugation approaches. In order to further enhance the shielding effectiveness (SE), a layer-by-layer architecture was constructed essentially with outer layers containing PC/PVDF blends with a MWNT–ferrite hybrid and the inner layers consisting of PC/PVDF blends with only MWNTs. An ultra-thin shield of 0.90 mm showed 499.9999% attenuation suggesting new pathways for designing lightweight, flexible EMI shielding materials.
To minimize electromagnetic (EM) pollution, two key parameters, namely, intrinsic wave impedance ... more To minimize electromagnetic (EM) pollution, two key parameters, namely, intrinsic wave impedance matching and intense absorption of incoming EM radiation, must satisfy the utmost requirements. To target these requirements, soft conducting composites consisting of binary blends of polycarbonate (PC) and poly(vinylidene fluoride) (PVDF) were designed with doped multiwalled carbon nanotubes (MWCNTs) and a three-dimensional cross-linked graphene oxide (GO) framework doped with ferrite nanoparticles. The doping of α-MnO 2 onto the MWCNTs ensured intrinsic wave impedance matching in addition to providing conducting pathways, and the ferrite-doped cross-linked GO facilitated the enhanced attenuation of the incoming EM radiation. This unique combination of magnetodielectric coupling led to a very high electromagnetic shielding efficiency (SE) of −37 dB at 18 GHz, dominated by absorption-driven shielding. The promising results from the composites further motivated us to rationally stack individual composites into a multilayer architecture following an absorption−multiple reflection−absorption pathway. This resulted in an impressive SE of −57 dB for a thin shield of 0.9-mm thickness. Such a high SE indicates >99.999% attenuation of the incoming EM radiation, which, together with the improvement in structural properties, validates the potential of these materials in terms of applications in cost-effective and tunable solutions.
Herein, we demonstrate that very high electromagnetic (EM) shielding efficiency can be achieved b... more Herein, we demonstrate that very high electromagnetic (EM) shielding efficiency can be achieved by dispersing nanoengineered FeCo anisometric nanostructures in a poly(vinylidene difluoride) matrix in the presence of conductive nanofillers (multiwall carbon nanotubes, MWCNTs). The FeCo nanorods (∼800 nm) and nanocubes (∼100 nm) were fabricated by a facile surfactant and polymer-assisted one-pot borohydride reduction method. The growth mechanism depicted a two-directional growth for cubes, whereas for nanorods, a unidirectional growth pattern across the (110) plane was evident. A total shielding effectiveness (SE T) of −44 dB at 18 GHz was achieved for a particular combination of FeCo nanorods and MWCNT, and for nanocube-based composites, it was found to be −39 dB at 18 GHz. It was observed from zero field cooled-field cooled curves that the samples displayed room temperature ferromagnetism. An excellent correlation between high aspect ratio FeCo nanorod and superior EM absorption (89%) was explored, pertaining to the fact that nanorods possessed higher magnetic saturation (177.1 emu/g) and coercivity (550 Oe) in contrast to the nanocubes with similar composition. Furthermore, theoretical insight into the mechanism revealed a high degree of interface scattering between conductive MWCNT and magnetic loss components, giving rise to an excellent synergy between magnetic and dielectric parts.
The fabrication of thin multilayer polymer nanocomposite films and their judicious arrangement in... more The fabrication of thin multilayer polymer nanocomposite films and their judicious arrangement in a sandwich structure to attenuate incoming electromagnetic (EM) radiation, mostly by absorption, is discussed herein. Two key properties (reasonably high conductivity, with high dielectric loss and magnetic permeability) were targeted here by using multiwall nanotubes (MWCNTs) and BaTiO 3 /Fe 3 O 4 (BT/Fe) co-doped graphene oxide (GO) sheets to design soft functional nanocomposites using bi-component blends of PC (polycarbonate) and PVDF (polyvinylidene fluoride). High dielectric loss and magnetic permeability were achieved by uniformly distributing BT and Fe nanoparticles on the huge specific surface area provided by the GO sheets. The MWCNTs were non-covalently modified to exfoliate the nanotubes and to get a well-connected structure of the blend components. The MWCNTs were thoroughly characterized by TEM, UV-vis, fluorescence emission, Raman and TGA. This surface modification of the MWCNTs also helps with their specific localization in the continuous bi-component blends. BT and Fe were co-doped onto the GO sheets by a well-designed step-by-step synthesis protocol, and the product can facilitate the absorption of incoming EM radiation. This hybrid structure was thoroughly characterized by various microscopic and spectroscopic techniques. By following a sequential mixing protocol, the BT/Fe co-doped GO sheets can be specifically localized in the PC components of the blends while the MWCNTs localize in the PVDF phase through a process driven by thermodynamics. This provides excellent heterogeneous boundaries with multiple scattering within the engineered nanostructures, in addition to retaining the conducting network and the associated dielectric loss properties. The resultant local field variation of such boundaries and the presence of highly lossy materials readily enhance the EM attenuation coefficient. The bulk compositions exhibited a high shielding effectiveness (SE) of À35 dB at 18 GHz (>85% absorption), and when rationally stacked into a multilayer architecture with absorption–multiple reflection–absorption pathways, the SE was further enhanced to À46 dB for a thin shield of 0.9 mm thickness. Such a high SE indicates >99.99% attenuation of the incoming EM radiation. This new-generation EM suppressor, distinguished by its multifunctionality and tunable dielectric and magnetic properties, hence offers an amendable, cost-effective replacement to existing solutions.
The world has dominated by automation, wireless communication and various electronic equipments, ... more The world has dominated by automation, wireless communication and various electronic equipments, which has led to the most undesirable offshoots like electromagnetic (EM) pollution. The rationale is environmental concern and the necessity to develop EM absorbing materials. This paper reviews the state of the art of designing polymer based nanocomposites containing nanoscopic particles with high electrical conductivity and complex microwave properties for enhanced EM attenuation. Given the brevity of this review article, herein we have summarized the high frequency millimetre wave absorbing properties of polymer nanocomposites consisting of various nanoparticles that either reflect or absorb microwave radiation like electrically conducting carbon nanotubes (CNTs) and graphene nanosheets (GNs), high dielectric constant ceramic nanoparticles that show relaxation loss in the microwave frequency and magnetic metal and ferrite nanoparticles that absorb microwave radiation through natural resonance, eddy current and hysteresis losses. Furthermore, we have stressed the necessity and impact of hybrid nanoparticles consisting of magnetic and dielectric nanoparticles along with conducting inclusions like CNT and GNs in this review. Electromagnetic interference (EMI) theory and necessary criterion for attenuation has been briefly discussed. The emphasis is made on various mechanisms towards EM attenuation controlled by these nanoparticles. Various structures developed using polymer nano-composites like bulk, foam and layered structures and their effect on EM attenuation has been elaborately discussed. In addition, various covalent/non-covalent modifications on nanoparticles have been juxtaposed in context to EM attenuation. In addition, we have highlighted important facets and direction for enhancing the microwave attenuation.
Nanoscale ordering in a polymer blend structure is indispensable to obtain materials with tailore... more Nanoscale ordering in a polymer blend structure is indispensable to obtain materials with tailored properties. It was established here that controlling the arrangement of nanoparticles, with different characteristics, in co-continuous PC/PVDF (polycarbonate/poly(vinylidene fluoride)) blends can result in outstanding microwave absorption (ca. 90%). An excellent reflection loss (R L) of ca. À71 dB was obtained for a model blend structure wherein the conducting (multiwall carbon nanotubes, MWNTs) and the magnetic inclusions (Fe 3 O 4) are localized in PVDF and the dielectric inclusion (barium titanate, BT) is in PC. The MWNTs were modified using polyaniline, which facilitates better charge transport in the blends. Furthermore, by introducing surface active groups on BT nanoparticles and changing the macroscopic processing conditions , the localization of BT nanoparticles can be tailored, otherwise BT nanoparticles would localize in the preferred phase (PVDF). In this study, we have shown that by ordered arrangement of nanoparticles, the incoming EM radiation can be attenuated. For instance, when PANI–MWNTs were localized in PVDF, the shielding was mainly through reflection. Now by localizing the conducting inclusion and the magnetic lossy materials in PVDF and the dielectric materials in PC, an outstanding shielding effectiveness of ca. À37 dB was achieved where shielding was mainly through absorption (ca. 90%). Thus, this study clearly demonstrates that lightweight microwave absorbers can be designed using polymer blends as a tool.
A unique approach was adopted to drive the multiwall carbon nanotubes (MWNTs) to the interface of... more A unique approach was adopted to drive the multiwall carbon nanotubes (MWNTs) to the interface of immiscible PVDF–ABS blends by wrapping the nanotubes with a mutually miscible homopolymer (PMMA). A tailor made interface with an improved stress transfer was achieved in the blends with PMMA wrapped MWNTs. This manifested in an impressive 108% increment in the tensile strength and 48% increment in the Young's modulus with 3 wt% PMMA wrapped MWNTs in striking contrast to the neat blends. As the PMMA wrapped MWNTs localized at the interface of PVDF–ABS blends, the electrical conductivity could be tuned with respect to only MWNTs, which were selectively localized in the PVDF phase, driven by thermodynamics. The electromagnetic shielding properties were assessed using a vector network analyser in a broad range of frequency, X-band (8–12 GHz) and K u-band (12–18 GHz). Interestingly, enhanced EM shielding was achieved by this unique approach. The blends with only MWNTs shielded the EM waves mostly by reflection however, the blends with PMMA wrapped MWNTs (3 wt%) shielded mostly by absorption (62%). This study opens new avenues in designing materials, which show simultaneous improvement in mechanical, electrical conductivity and EM shielding properties.
A unique strategy was adopted here to improve the compatibility between the components of an immi... more A unique strategy was adopted here to improve the compatibility between the components of an immiscible polymer blend and strengthen the interface. PMMA, a mutually miscible polymer to both PVDF and ABS, improved the compatibility between the phases by localizing at the blends interface. This was supported by the core–shell formation with PMMA as the shell and ABS as the core as observed from the SEM micrographs. This phenomenon was strongly contingent on the concentration of PMMA in the blends. This strategy was further extended to localize graphene oxide (GO) sheets at the blends interface by chemically coupling it to PMMA (PMMA-g-GO). A dramatic increment of ca. 84% in the Young's modulus and ca. 124% in the yield strength was observed in the presence of PMMA-g-GO with respect to the neat blends. A simultaneous increment in both the strength and the modulus was observed in the presence of PMMA-g-GO whereas, only addition of GO resulted in a moderate improvement in the yield strength. This study reveals that a mutually miscible polymer can render compatibility between the immiscible pair and can improve the stress transfer at the interface.
In order to obtain better materials, control over the precise location of nanoparticles is indisp... more In order to obtain better materials, control over the precise location of nanoparticles is indispensable. It is shown here that ordered arrangements of nanoparticles, possessing different characteristics (electrical/ magnetic dipoles), in the blend structure can result in excellent microwave absorption. This is manifested from a high reflection loss of ca. −67 dB for the best blend structure designed here. To attenuate electromagnetic radiation, the key parameters of high electrical conductivity and large dielectric/magnetic loss are targeted here by including a conductive material [multiwall carbon nanotubes, MWNTs], ferroelectric nanostructured material with associated relaxations in the GHz frequency [barium titanate, BT] and lossy ferromagnetic nanoparticles [nickel ferrite, NF]. In this study, bi-continuous structures were designed using 50/50 (by wt) blends of polycarbonate (PC) and polyvinylidene fluoride (PVDF). The MWNTs were modified using an electron acceptor molecule, a derivative of perylenediimide, which facilitates π–π stacking with the nanotubes and stimulates efficient charge transport in the blends. The nanoscopic materials have specific affinity towards the PVDF phase. Hence, by introducing surface-active groups, an ordered arrangement can be tailored. To accomplish this, both BT and NF were first hydroxylated followed by the introduction of amine-terminal groups on the surface. The latter facilitated nucleophilic substitution reactions with PC and resulted in their precise location. In this study, we have shown for the first time that by a compartmentalized approach, superior EM attenuation can be achieved. For instance, when the nanoparticles were localized exclusively in the PVDF phase or in both the phases, the minimum reflection losses were ca. −18 dB (for the MWNT/BT mixture) and −29 dB (for the MWNT/NF mixture), and the shielding occurred primarily through reflection. Interestingly, by adopting the compartmentalized approach wherein the lossy materials were in the PC phase and the conductive materials (MWNT) were in the PVDF phase, outstanding reflection losses of ca. −57 dB (for the BT and MWNT combination) and −67 dB (for the NF and MWNT combination) were noted and the shielding occurred primarily through absorption. Thus, the approach demonstrates that nanoscopic structuring in the blends can be achieved under macroscopic processing conditions and this strategy can further be explored to design microwave absorbers.
Multiwall carbon nanotubes (MWNTs) were anchored onto graphene oxide sheets (GOs) via diazonium a... more Multiwall carbon nanotubes (MWNTs) were anchored onto graphene oxide sheets (GOs) via diazonium and C–C coupling reactions and characterized by spectroscopic and electron microscopic techniques. The thus synthesized MWNT–GO hybrid was then melt mixed with 50/50 polyamide6– maleic anhydride-modified acrylonitrile-butadiene-styrene (PA6–mABS) blend to design materials with high dielectric constant (3 0) and low dielectric loss. The phase morphology was studied by SEM and it was observed that the MWNT–GO hybrid was selectively localized in the PA6 phase of the blend. The 3 0 scales with the concentration of MWNT–GO in the blends, which interestingly showed a very low dielectric loss (<0.2) making them potential candidate for capacitors. In addition, the dynamic storage modulus scales with the fraction of MWNT–GO in the blends, demonstrating their reinforcing capability as well.
Herein, we report tailor-made properties by dispersing nanostructured materials in a co-continuou... more Herein, we report tailor-made properties by dispersing nanostructured materials in a co-continuous polymer blend (PVDF/ABS) that is capable of shielding electromagnetic (EM) radiation. To accomplish this, lossy materials were employed like multi-walled carbon nanotubes (MWNTs), and barium titanate (BT), (which exhibit relaxation losses in the microwave frequency domain) and ferrites (like Fe 3 O 4 ). To improve the state of dispersion, the MWNTs were non-covalently modified using 3,4,9,10-perylenetetracarboxylic dianhydride (PTCD) via π-π stacking, and for effective shielding the MWNTs were conjugated with either BT or Fe 3 O 4 nanoparticles through suitable modifications. The hybrid nanoparticles were selectively localized in the PVDF phase, governed by its polarity, and exhibited excellent microwave attenuation. In order to gain insight into the dielectric and magnetic attributes, the microwave parameters were assessed systematically. Taken together, our results uncover polymer blend as a promising candidate for designing lightweight, thermally stable microwave absorber materials.
Lightweight and flexible electromagnetic shielding materials were designed by selectively localiz... more Lightweight and flexible electromagnetic shielding materials were designed by selectively localizing multiwall carbon nanotubes (MWNTs) anchored magnetic nanoparticles in melt mixed co-continuous blends of polyvinylidene fluoride (PVDF) and poly(styrene-co-acrylonitrile) (SAN). In order to facilitate better dispersion, the MWNTs were modified using pyrenebutyric acid (PBA) via p–p stacking. While one of the two-targeted properties, i.e., high electrical conductivity, was achieved by PBA modified MWNTs, high magnetic loss was accomplished by introducing nickel (NF) or cobalt ferrites (CF). Moreover, the attenuation by absorption can be tuned either by using NF (58% absorption) or CF (64% absorption) in combination with PBA-MWNTs. More interestingly, when CF was anchored on to MWNTs via the pyrene derivative, the minimum reflection loss attained was À55 dB in the Ku band (12–18 GHz) frequency and with a large bandwidth. In addition, the EM waves were blocked mostly by absorption (70%). This study opens new avenues in designing flexible and lightweight microwave absorbers.
Highly conducting composites were derived by selectively localizing multiwall carbon nanotubes (M... more Highly conducting composites were derived by selectively localizing multiwall carbon nanotubes (MWNTs) in co-continuous PVDF/ABS (50/50, wt/wt) blends. The electrical percolation threshold was obtained between 0.5 and 1 wt% MWNTs as manifested by a dramatic increase in the electrical conductivity by about six orders of magnitude with respect to the neat blends. In order to further enhance the electrical conductivity of the blends, the MWNTs were modified with amine terminated ionic liquid (IL), which, besides enhancing the interfacial interaction with PVDF, facilitated the formation of a network like structure of MWNTs. This high electrical conductivity of the blends, at a relatively low fraction (1 wt%), was further explored to design materials that can attenuate electromagnetic (EM) radiation. More specifically, to attenuate the EM radiation by absorption, a ferroelectric phase was introduced. To accomplish this, barium titanate (BT) nanoparticles chemically stitched onto graphene oxide (GO) sheets were synthesized and mixed along with MWNTs in the blends. Intriguingly, the total EM shielding effectiveness (SE) was enhanced by ca. 10 dB with respect to the blends with only MWNTs. In addition, the effect of introducing a ferromagnetic phase (Fe 3 O 4) along with IL modified MWNTs was also investigated. This study opens new avenues in designing materials that can attenuate EM radiation by selecting either a ferroelectric (BT–GO) or a ferromagnetic phase (Fe 3 O 4) along with intrinsically conducting nanoparticles (MWNTs).
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Papers by Sourav Biswas