Goutam Prasanna Kar

Tailoring the dispersion of multiwall carbon nanotubes in co-continuous PVDF/ABS blends to design materials with enhanced electromagnetic interference shielding

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 (Fe3O4) 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 (Fe3O4) along with intrinsically conducting nanoparticles (MWNTs).

Microwave absorbers designed from PVDF/SAN blends containing multiwall carbon nanotubes anchored cobalt ferrite via a pyrene derivative

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 π–π 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 −55 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.

Nanoparticle-Driven Intermolecular Cooperativity and Miscibility in Polystyrene/Poly(vinyl methyl ether) Blends

The effect of silver nanoparticles (nAg) in PS/PVME [polystyrene/poly(vinyl methyl ether)] blends was studied with respect to the evolution of morphology, demixing temperature, and segmental dynamics. In the early stage of demixing, PVME developed an interconnected network that coarsened in the late stage. The nAg induced miscibility in the blends as supported by shear rheological measurements. The physicochemical processes that drive phase separation in blends also led to migration of nAg to the PVME phase as supported by AFM. The segmental dynamics was greatly influenced by the presence of nAg due to the specific interaction of nAg with PVME. Slower dynamics and an increase in intermolecular cooperativity in the presence of nAg further supported the role of nAg in delaying the phase separation processes and augmenting the demixing temperature in the blends. Different theoretical models were assessed to gain insight into the dynamic heterogeneity in PS/PVME blends at different length scales.

Tuning the microwave absorption through engineered nanostructures in co-continuous polymer blends

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 Fe3O4). To improve the state of dispersion, the MWNTs were non-covalently modified using 3,4,9,10-perylenetetracarboxylic dianhydride (PTCD) via pi-pi stacking, and for effective shielding the MWNTs were conjugated with either BT or Fe3O4 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.

A unique strategy towards high dielectric constant and low loss with multiwall carbon nanotubes anchored onto graphene oxide sheets

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 (e′) 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 e′ 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.

Synergistic effect of polymorphism, substrate conductivity and electric field stimulation towards enhancing muscle cell growth in vitro

Poly(vinylidene difluoride), a well-known candidate for artificial muscle patch applications is a semi-crystalline polymer with a host of attributes such as piezo- and pyroelectricity, polymorphism along with low dielectric constant and stiffness. The present work explores the unique interplay among the factors (conductivity, polymorphism and electrical stimulation) towards cell proliferation on poly(vinylidene difluoride) (PVDF)-based composites. In this regard, multi-walled carbon nanotubes (MWNTs) are introduced in the PVDF matrix (limited to 2%) through melt mixing to increase the conductivity of PVDF. The addition of MWNTs also led to an increase in the fraction of piezoelectric β-phase, tensile strength and modulus. The melting and crystallization behaviour of PVDF–MWNT together with FT-IR confirms that the crystallization is found to be aided by the presence of MWNT. The conducting PVDF–MWNTs are used as substrates for the growth of C2C12 mouse myoblast cells and electrical stimulation with a range of field strengths (0–2 V cm−1) is intermittently delivered to the cells in culture. The cell viability results suggest that metabolically active cell numbers can statistically increase with electric stimulation up to 1 V cm−1, only on the PVDF + 2% MWNT. Summarising, the current study highlights the importance of biophysical cues on cellular function at the cell–substrate interface. This study further opens up new avenues in designing conducting substrates, that can be utilized for enhancing cell viability and proliferation and also reconfirms the lack of toxicity of MWNTs, when added in a tailored manner.

Lightweight, flexible and ultra-thin sandwich architectures for screening electromagnetic radiation

A lightweight and flexible multilayer structure consisting of poly(vinylidene fluoride) and iron particles deposited (electroless) on to a carbon nanofiber (CF) mat was successfully fabricated for electromagnetic interference shielding (EMI) application. The CF was pre-activated before depositing the iron particles by an electroless deposition technique. To enhance the shielding, a poly(vinylidene fluoride) PVDF composite containing multiwalled carbon nanotubes (MWNT) was sandwiched as an inner layer between two outer layers of iron particles deposited onto the CF mat (Fe@CF). The electroless deposition of iron particles onto the CF mat is reflected in a dramatically enhanced SE of ca. −54 dB (at 18 GHz) for an ultra-thin sheet of 0.6 mm as compared to the controlled sandwich structure (consisting of PVDF/CF) due to the presence of a conducting MWNT/PVDF film and magnetically active Fe@CF layer. This particular structure exhibits >95% absorption of the incoming EM radiation. Such a lightweight and flexible sandwich structure promises protection against EM microwave radiation.

A high-performance BaTiO3-grafted-GO-laden poly(ethylene oxide)-based membrane as an electrolyte for all-solid lithium-batteries

Nanocomposite polymer electrolytes (NCPEs) comprising poly(ethylene oxide) (PEO), barium titanate-grafted-graphene oxide (BaTiO3-g-GO) and lithium bis(trifluoromethanesulfonyl imide) (LiTFSI) were prepared by a simple hot-press technique. An increase of two orders of magnitude in the ionic conductivity was achieved upon incorporation of BaTiO3-g-GO in the polymeric matrix even at 0 °C. The addition of BaTiO3-g-GO as a filler has significantly enhanced the thermal stability and mechanical integrity of the membrane. The BaTiO3-g-GO-laden membrane was found to have better interfacial properties with a lithium metal anode than the filler-free membrane. Charge–discharge studies revealed a stable cycling profile even at 5C-rate and it was found to be superior to those reported earlier.