Narayan Chandra Das

Effect of processing parameters, applied pressure and temperature on the electrical resistivity of rubber-based conductive composites

Abstract Carbon black- and short carbon fibre (SCF)-filled conductive composites were prepared from ethylene vinyl acetate (EVA), ethylene propylene diene (EPDM) rubber and their 50:50 blend. The electrical resistivity of carbon black- and SCF-filled composites were measured under different conditions. The electrical conductivity of filled polymer composites is due to the formation of a continuous conductive network in the polymer matrix. These conductive networks involve specific arrangement of conductive elements so that the electrical paths are formed for free movement of electrons. It was found that electrical conductivity of filled conductive composites depends on different processing parameters like mixing time, rotor speed, mixing temperature, vulcanization time and pressure and service conditions like applied pressure and temperature. The results of different experiments have been discussed in light of break down and formation of the continuous conductive network.

Simple cubic super crystals containing PbTe nanocubes and their core-shell building blocks.

We report a preparation of high-quality cubic PbTe nanocrystals and their assembly into both square-array, two-dimensional patterns and three-dimensional simple cubic super crystals. The influence of oleylamine in the nanocrystal synthesis and core-shell formation through an anion-exchange mechanism was also studied. The simple cubic super crystals together with two-dimensional assembly patterns containing PbTe nanocubes and their core-shell building blocks were examined using TEM, SEM, AFM, XRD, SAXS, and FTIR. Such super crystals consisting of cubic structural building blocks may allow engineering of more complex materials from which novel properties may emerge.

Electromagnetic Interference Shielding Effectiveness of Hybrid Conductive Polymer Composite

Electromagnetic interference (EMI) shielding characteristics of ethylene vinyl acetate (EVA) and ethylene propylene diene (EPDM) and their 50: 50 blend filled with conductive carbon black and short carbon fibre (SCF) have been studied. The measurements of shielding effectiveness (SE) were carried out in two different frequency ranges 100-2000 MHz and 8-12 GHz (X-band range). The return loss and the loss due to absorption were also measured as a function of frequency in the X-band range and microwave region. It is observed that the SE of the composites is frequency dependent, especially at higher frequency range, and it increases with increasing frequency. The SE also increases with the increase in filler loading. It was found that electromagnetic waves interact with the material via the impurities, inclusions and voids existing in the bulk composites. The SCF-filled composites show higher SE compared to that of conductive carbon black. The correlation between SE and conductivity of the various composites is also discussed. The results suggest that the fibre-filled (20 phr) composites can be used for the EMI shielding, as well as for some microwave applications.

Synthesis and characterization of graphene oxide filled ethylene methyl acrylate hybrid nanocomposites

Graphene oxide (GO) filled ethylene methyl acrylate (EMA) hybrid nanocomposites containing both organic–inorganic features were prepared through a solution mixing method. The morphologies of the graphene oxide within the polymer matrices were examined by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM). Enhanced dispersion of GO through EMA by exfoliation of the graphene oxide layers were confirmed by X-ray diffraction (XRD) analysis and this value is also supported by the RMS roughness value obtained from AFM analysis. Raman spectroscopy studies revealed the impact of graphene oxide destratification as well as changing of graphene oxide affectivity in the presence of elastomeric media. The physico–mechanical properties of the composites extensively depend on the filler loading, exfoliation of graphene oxide layers, and polymer–filler interaction. Interactions between various oxygen containing groups of chemically derived GO and EMA enhance thermal stability more than pure polymer as shown by thermogravimetric (TGA) and differential scanning calorimetry (DSC) analysis.

A simplistic approach to green future with eco-friendly luminescent carbon dots and their application to fluorescent nano-sensor ‘turn-off’ probe for selective sensing of copper ions

Zero-dimensional fluorescent nanoparticles having specificity as molecular probe appears to be strategically balanced fluorescent nano-probes. In this work, purified lemon extract and l-arginine have been thermally coupled for the extremely acute detection of Cu2+ in aqueous medium. The Cu2+ ions may be captured by the amino groups on the surface of the nano-sensor to form cupric ammine complex resulting in quenched fluorescence via an inner filter effect. Our proposed nano-probe is N-doped carbon dots (NCDs) which are efficiently selective as fluorescent chemosensor due to enormous binding affinity towards Cu2+ in a wide range of concentration (0.05-300μM) within a few minutes.

Conductive rubbers made by adding conductive carbon black to EVA, EPDM, and EVA–EPDM blends

Abstract Electrically conductive rubbers have been prepared by the incorporation of conductive carbon black into ethylene/vinyl acetate (EVA) copolymers, ethylene/propylene/diene monomer (EPDM) terpolymers, and a 50 : 50 EVA–EPDM blend. The electrical and mechanical properties of these composites have been studied. The percolation limit for high conductivity in the filled rubbers depends on their compatibility as well as the viscosity and polarity of the rubbers. The electrical resistivity decreases with increasing temperature and the activation energy for conduction decreases with increasing filler loading. The temperature dependence of resistivity can be correlated with data from DSC, XRD, and DMTA measurements. Electrical set and electrical hysteresis have been observed during heating–cooling cycles. The change in resistivity with applied pressure is also reported.

Synthesis of a novel pH responsive phyllosilicate loaded polymeric hydrogel based on poly(acrylic acid-co-N-vinylpyrrolidone) and polyethylene glycol for drug delivery: modelling and kinetics study for the sustained release of an antibiotic drug

In this study, we developed a novel pH-sensitive composite interpenetrating polymeric network (IPN) hydrogel based on polyethylene glycol (PEG) and poly(acrylic acid-co-N-vinylpyrrolidone) crosslinked with N,N-methylenebisacrylamide (MBA). This composite was used for the controlled release (CR) of cefadroxil, an antibiotic drug. A systematic method via in situ polymerization in sodium aluminosilicate dispersion media was also performed to achieve a much higher degree of swelling behaviour followed by sufficient gel strength in the simulated pH atmosphere. The resulting hydrogel imprinted was characterized by Fourier transform infrared spectroscopy (FTIR) to confirm the copolymer formation and cross linking reaction, and scanning electron microscopy (SEM) to understand the surface morphology. Differential thermal analysis thermogravimetric analysis (DTA-TGA) and X-ray diffraction (XRD) were also performed to investigate the deviations from crystallinity and swelling experiments. The in vitro release of the drug loaded hydrogel performed in the acidic and basic media affected the drug release characteristics. The release data was analysed using an empirical equation to understand the transport of a drug-containing solution through the polymeric matrices. The wt% of PEG, MBA, initiator, total monomer concentration, pH of the medium was found to strongly influence the drug release behaviour of the gels. The impression of drug loading on the encapsulation efficiency was also investigated. The release rate of the drug was much faster at pH 7.8 than at pH 1.7. The modelling and kinetics of sustained release of antibiotic is reported.

Green approach to photoluminescent carbon dots for imaging of gram-negative bacteria Escherichia coli

Fluorescent carbon dots, zero-dimensional nanomaterials with surface ligands, have been studied extensively over the past few years in biolabelling or fluorescence-based live cell assays. In the past, synthetic organic dyes have been used as cell tracking materials, but they have severe limitations; fluorescent carbon dots may pave the way to biolabelling and cell imaging. In this work, green fluorescent carbon dots have been synthesized from a green source, gram, without any sort of covalent or ionic modifications. These gram-derived carbon dots are unique with respect to synthetic commercial cell-tracking dyes as they are non-toxic, cell internalization occurs quickly, and they have excellent bioconjugation with bacterial cells. Our aim is to establish these carbon dots in a biolabelling assay with its other physicochemical features like the tunable luminescence property, high degree of water solubility and low toxicity, towards various environments (wide range of pH, high ionic strength). Our study introduces a new perspective on the commercialization of carbon dots as a potential alternative to synthetic organic dyes for fluorescence-based cell-labelling assays.

Synthesis of polydopamine-coated halloysite nanotube-based hydrogel for controlled release of a calcium channel blocker

A stimuli-triggered drug delivery vehicle has been synthesized by self-polymerization of dopamine (DA) on the outer surface of halloysite nanotubes (HNT) followed by gelation via alginate. DA in aqueous medium is made to adhere on outer surface of lumen and self-polymerizes in alkaline medium. Self-polymerized DA (PDA)-coated HNTs have been incorporated into alginate hydrogel and ionically crosslinked. Scanning electron microscope and transmission electron microscope images imply a coating of PDA of 12–17 nm in thickness on the HNT surface. The rheological behavior of the hydrogels as prepared can reveal their shear thinning character and they show sufficient gel strength (prominent difference between elastic and loss modulus). The thermal decay profile from thermogravimetric analysis implies the superior thermal stability with respect to pristine alginate. The action of PDA as an additional effective gelator has been noticed and confirmed by swelling trends in aqueous media. Drug loading has been achieved by two procedures: one is in situ loading and the other one is post-loading. It has been noticed that in situ loading of drug molecules during polymerization process of DA on HNT surface shows better controlled release feature than post-loading. Such release behavior was also tuned by altering the synthesis parameters.

The photovoltaic performance of ZnO nanorods in bulk heterojunction solar cells

A novel approach has been followed for synthesizing vertically aligned ZnO nanorods (ZONRs) on indium tin oxide (ITO) coated glass substrates for photovoltaic applications. The fabricated ZONR arrays have been used to construct bulk heterojunction photovoltaic devices together with pristine poly-(3-hexylthiophene) (P3HT) or (6,6)-phenyl C61 butyric acid methyl ester (PCBM) and P3HT blends, respectively. Scanning electron microscopy, X-ray diffraction, photoluminescence, UV-vis absorption spectroscopy, and photovoltaic measurements were performed to study the morphology and device performance of the prepared structures. The typical microstructure of the vertically aligned ZONR arrays plays an important role in collecting the photo-generated electrons and acts as conducting paths to the ITO electrode. Fill factor of the devices increased from 35% to 47% when the PCBM was introduced, which directly contributed to the enhancement of the power conversion efficiencies up to 1.23%.