A. Kumar

Effects of 160 MeV Ni12+ ion irradiation on HCl doped polyaniline electrode

Conducting polymers are suitable as electrode materials for high performance supercapacitors because of their high specific capacitance and high dc conductivity in the charged state. Ion beam (energy >1 MeV) irradiation of materials is a novel technique to modify their properties. Polyaniline conducting polymer thin films doped with HCl are synthesized electrochemically on indium tin oxide coated glass substrates and are irradiated with 160 MeV Ni12+ ions at different fluences, namely, 5 × 1010, 5 × 1011 and 3 × 1012 ions cm−2. The dc conductivity measurements of the irradiated films showed up to 70% increase in conductivity, which may be due to the increase of carrier concentration in the polymer film as observed in UV-Vis spectroscopy and other effects like the cross linking of polymer chains, bond breaking and creation of defects sites. An x-ray diffractogram study shows that the degree of crystallinity of polyaniline increases upon swift heavy ion (SHI) irradiation with the increase in ion fluence. The capacitance of the irradiated films is lowered but that of the supercapacitors with irradiated films showed enhanced electrochemical stability compared with the devices with unirradiated films while characterized for a cycle life up to 10 000 cycles. This effect could possibly be ascribed to the stabilization of volatile surface groups upon SHI irradiation.

Biocompatible novel starch/polyaniline composites: Characterization, anti-cytotoxicity and antioxidant activity

Starch/polyaniline composites have been synthesized using oxidative polymerization of polyaniline in an aqueous dispersion of starch isolated from Colocasia esculenta corm. Scanning electron micrographs reveals the growth of polyaniline over the surface of the starch granules. DPPH scavenging and haemolysis prevention assay have been performed to estimate the antioxidant activity and cytotoxicity of the composites. Formation of new properties of the composites as compared to starch and poloyaniline was evident from the X-ray diffraction analysis (XRD). Characterization done using UV-Vis, FTIR and DSC analysis provide evidence of composite formation. Composite possesses antioxidant nature which increases with the concentration of polyaniline. The haemolysis prevention activity of these novel composite materials is found to increase as compared to the pure polyaniline with minor compromise in the antioxidant activity. The materials show tremendous potential for biomedical applications.

Antioxidant activity and haemolysis prevention efficiency of polyaniline nanofibers.

Polyaniline (PAni) nanofibers have been synthesized by interfacial polymerization using hydrochloric acid (HCl) and camphor sulfonic acid (CSA) as dopants. The powder x-ray diffraction pattern of bulk polyaniline reveals ES I structure and has been indexed in a pseudo-orthorhombic lattice. The broadening of (110) reflection in the nanofiber samples has been analysed in terms of domain length and strain using a convolution method employing a Voigt function. The increase in d spacing for the (110) reflection in HCl-doped PAni nanofibers have been assigned to the change in structural conformation due to the increase in the tilt angle of the polymer chain, which is also evident from microRaman spectra. UV-vis spectra of the PAni nanofibers exhibit a remarkable blueshift in the absorption bands attributed to pi-pi* and pi-polaron band transitions indicating a reduction in particle size, which is also observed in TEM micrographs. The antioxidant activity of the polyaniline nanofiber samples has been investigated using 1,1-diphenyl-2-picrylhydrazyl (DPPH) scavenging assay by employing UV-visible spectroscopy. It has also been observed that polyaniline nanofibers are able to protect the haemolysis of red blood cells (RBCs) from cytotoxic agents, namely H(2)O(2). The observed enhancement in the antioxidant and haemolysis prevention activity of the PAni nanofibers as compared to bulk has been attributed to the reduction in particle size and changes in structural conformation, as evident from TEM, XRD and microRaman spectroscopy.

Experimental studies on poly methyl methacrylate based gel polymer electrolytes for application in electrical double layer capacitors

Studies have been carried out on gel polymer electrolytes comprising poly methyl methacrylate (PMMA)-ethylene carbonate (EC)–propylene carbonate (PC)–salts, LiClO4, NaClO4 and (C2H5)4NClO4 (TEAClO4) with a view to using them as electrolytes in electrical double layer capacitors (EDLCs) based on activated charcoal powder electrodes. The optimum composition of gel electrolytes, PMMA (20 wt%)–EC : PC (1 : 1 v/v)–1.0 M salts exhibit high ionic conductivity of the order of ~10−3 S cm−1 at room temperature with good mechanical/dimensional stability, suitable for their application in EDLCs. The EDLCs have been characterized using linear sweep cyclic voltammetry, galvanostatic charge–discharge tests and ac impedance spectroscopy. The values of capacitance of 68–151 mF cm−2 (equivalent to single electrode specific capacitance of 38–78 Fg−1 of activated charcoal powder) have been observed. These values correspond to a specific energy of 5.3–10.8 Wh kg−1 and a power density of 0.19–0.22 kW kg−1. The capacitance values have been observed to be stable up to 5000 voltammetric cycles or even more. A comparison of studies shows the predominant role of anions of the gel electrolytes in the capacitive behaviour of EDLCs.

Antibacterial and hemolysis activity of polypyrrole nanotubes decorated with silver nanoparticles by an in-situ reduction process

Polypyrrole nanotube-silver nanoparticle nanocomposites (PPy-NTs:Ag-NPs) have been synthesized by in-situ reduction of silver nitrate (AgNO3) to suppress the agglomeration of Ag-NPs. The morphology and chemical structure of the nanocomposites have been studied by HRTEM, SEM, XRD, FTIR and UV-vis spectroscopy. The average diameter of the polypyrrole nanotubes (PPy-NTs) is measured to be 130.59±5.5 nm with their length in the micrometer range, while the silver nanoparticles (Ag-NPs) exhibit spherical shape with an average diameter of 23.12±3.23 nm. In-vitro blood compatibility of the nanocomposites has been carried out via hemolysis assay. Antimicrobial activity of the nanocomposites has been investigated with Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) bacteria. The results depict that the hemolysis and antimicrobial activities of the nanocomposites increase with increasing Ag-NP concentration that can be controlled by the AgNO3 precursor concentration in the in-situ process.

Study of Li3+ ion irradiation effects in P(VDF-HFP) based gel polymer electrolytes for application in Li-ion battery

Swift heavy ion (SHI) irradiation of P(VDF–HFP)–(PC+DEC)–LiClO4 gel polymer electrolyte system with 48 MeV Li3+ ion having five different fluences were investigated with a view to increasing the Li+ ion diffusivity in the electrolyte. Irradiation with SHI shows enhancement of conductivity at lower fluences and decrease in conductivity at higher fluences with respect to unirradiated polymer electrolyte films. Maximum room temperature (303 K) ionic conductivity is found to be 2.2 × 10−2 S cm−1 after irradiation with fluence of 1011 ions cm−2. This interesting result could be ascribed to the fluence dependent change in porosity and to the fact that for a particular ion beam with a given energy higher fluence provides critical activation energy for cross linking and crystallization to occur, which results in a decrease in ionic conductivity. XRD results show a decrease in the degree of crystallinity upon ion irradiation at low fluences (≤1011 ions cm−2) and an increase in crystallinity at high fluences (>1011 ions cm−2). Analysis of FTIR results suggests the bond breaking at a fluence of 5 × 1010 ions cm−2 and cross linking at a fluence of 5 × 1012 ions cm−2 which corroborate the conductivity and XRD results. Scanning electron micrographs exhibit increased porosity of the polymer electrolyte films after ion irradiation.

Dielectric spectroscopy for probing the relaxation and charge transport in polypyrrole nanofibers

Conductivity relaxation and charge transport mechanisms in polypyrrole (PPy) nanofibers synthesized using a micellar polymerization technique with varying surfactant concentration has been investigated by dielectric relaxation spectroscopy. TEM micrographs depict that the increasing surfactant concentration leads to the reduction of the nanofiber diameter. X-ray diffraction studies show that domain length in the PPy nanofibers decreases with decreasing fiber diameter whereas the strain caused due to dislocations and point defects increases. The permittivity spectra reveal that the relaxation mechanism in PPy nanofibers are dominated by hopping of trapped charges. Two relaxation peaks in the impedance spectra are attributed to the two-phase structure in the PPy nanofibers; the lower frequency peak is ascribed to the phase of oxidized repeat units and the higher frequency peak to the reduced repeat units of PPy nanofibers. The occurrence of relaxation peaks at different frequencies in the impedance and modu...

Swift heavy ion irradiation induced enhancement in the antioxidant activity and biocompatibility of polyaniline nanofibers

Polyaniline (PAni) nanofibers doped with HCl and CSA have been irradiated with 90 MeV O(7+) ions with fluence of 3 x 10(10), 3 x 10(11) and 1 x 10(12) ions cm(-2). TEM micrographs show a decrease in the fiber diameter with increasing irradiation fluence, which has been explained on the basis of the Coulomb explosion model. XRD analysis reveals a decrease in the crystalline domain length and an increase in the strain. The increase in d-spacing for the (100) reflection with increasing irradiation fluence is ascribed to the increase in the tilt angle of the polymer chain, which is also evident from micro-Raman spectra. UV-vis spectra of the PAni nanofibers exhibit blue-shift in the absorption bands attributed to pi-pi* band transitions indicating a reduction in particle size after SHI irradiation; as also observed in TEM micrographs. Micro-Raman spectra also reveal a transition from the benzenoid to quinoid structures in the PAni chain as the fluence is increased. Although the quinoid unit has no hydrogen for DPPH scavenging, the antioxidant activity of PAni nanofibers is found to increase with increasing fluence. This has been attributed to the availability of more reaction sites as a result of fragmentation of the PAni nanofibers which compensates for the benzenoid to quinoid transition after irradiation. The biocompatibility of the PAni nanofibers is also found to increase with increasing irradiation fluence, indicating the possibility of employing swift heavy ion irradiation as an effective technique in order to modify conducting polymer nanostructures for biomedical applications.

Ionic conduction in 70-MeV C5+-ion-irradiated poly(vinylidenefluoride-co-hexafluoropropylene)-based gel polymer electrolytes

In an attempt to increase the Li+-ion diffusivity, poly(vinylidenefluoride-co-hexafluoropropylene)-(propylene carbonate+diethyl carbonate)-lithium perchlorate gel polymer electrolyte system has been irradiated with 70-MeV C5+-ion beam of nine different fluences. Swift heavy-ion irradiation shows enhancement in ionic conductivity at lower fluences and decrease in ionic conductivity at higher fluences with respect to unirradiated gel polymer electrolyte films. Maximum room-temperature (303K) ionic conductivity is found to be 2×10−2S∕cm after irradiation with a fluence of 1011ions∕cm2. This interesting result could be attributed to the fact that for a particular ion beam with a given energy, a higher fluence provides critical activation energy for cross linking and crystallization to occur, which results in the decrease in ionic conductivity. X-ray-diffraction results show decrease in the degree of crystallinity upon ion irradiation at low fluences (⩽1011ions∕cm2) and increase in crystallinity at higher flue...

Fluorescence enhancement of glutaraldehyde functionalized polyaniline nanofibers in the presence of aromatic amino acids

Polyaniline nanofibers (PNFs) synthesized by dilute polymerization method have been surface functionalized with glutaraldehyde at their N-terminals in Phosphate Buffered Saline (PBS) at P(H)=7.4 in order to achieve improved interaction of surface functionalized polyaniline nanofibers (SF-PNFs) with aromatic amino acids-Tyrosine, Tryptophan and Phenylalanine through incorporation of aldehyde (-CHO) and hydroxyl (-OH) functionalities. HRTEM reveals nanofibers of average diameter of 35.66 nm. FESEM depicts interconnected networks of nanofibers of polyaniline (PAni). UV-visible absorption and Fluorescence spectroscopy indicate that the PNFs and SF-PNFs are in emeraldine base (EB) form. FT-IR, (1)H NMR spectroscopy suggests covalent interactions of SF-PNFs with aromatic amino acids and possible reaction mechanisms have been proposed based on these results. Remarkable enhancement in fluorescence signals of SF-PNFs in the presence of aromatic amino acids has been observed and the apparent binding constant (KA) and the number of binding sites (n) have been calculated using fluorescence enhancement equation. The KA value is found to be highest for SF-PNFs+Tyrosine and n is two for all the polymer amino acid complexes, which are in agreement with the FT-IR and (1)H NMR results. Fluorescence resonance energy transfer (FRET) efficiency has been found to be highest for SF-PNFs+Tyrosine giving maximum fluorescence enhancement. The study of interaction mechanisms by means of an extremely sensitive technique like fluorescence using SF-PNFs as a substrate may provide a promising analytical tool for detection and monitoring any biochemical reactions involving these three aromatic amino acids.