Ajit R. Kulkarni

Complex permittivity characteristics of epoxy nanocomposites at low frequencies

The complex permittivity characteristics of epoxy nanocomposite systems were examined and an attempt has been made to understand the underlying physics governing some of the unique macroscopic dielectric behaviors. The experimental investigations were performed using two different nanocomposite systems with low filler concentrations over the frequency range of 10-2-400 Hz, but for some cases, the data has been reported upto 106 Hz for a better understanding of the behaviors. Results demonstrate that nanocomposites do possess unique permittivity behaviors as compared to those already known for unfilled polymer and microcomposite systems. The nanocomposite real permittivity and tanδ values are found to be lower than that of unfilled epoxy. In addition, results show that interfacial polarization and charge carrier mobilities are suppressed in epoxy nanocomposite systems. The complex permittivity spectra coupled with the ac conductivity characteristics with respect to frequency was found to be sufficient to identify several of the nanocomposite characteristics like the reduction in permittivity values, reduction in the interfacial polarization mechanisms and the electrical conduction behaviors. Analysis of the results are also performed using electric modulus formalisms and it has been seen that the nanocomposite dielectric behaviors at low frequencies can also be explained clearly using this formalism.

Electrical behaviour of attritor processed Al/PMMA composites

Abstract Al/PMMA composites containing different volume fractions of aluminium were prepared by attritor milling followed by hot pressing and their thermal expansion and electrical behaviour were studied. Room temperature resistivity of these composites dropped by several orders of magnitude when the volume percent of aluminium ranged between 20 and 40 vol.%. Microstructural examination revealed the presence of continuous chains of aluminium in highly conducting composites. The dielectric constant and dissipation factor of the composites increased with increase in aluminium content. This has been attributed to the interfacial polarization associated with aluminium particles.

Dielectric and microstructure studies of lead magnesium niobate prepared by partial oxalate route

Abstract Lead magnesium niobate (PMN) has been prepared using the partial oxalate method without addition of excess PbO and sintering at four different temperatures, 900, 1000, 1100 and 1200 °C. Increase in the sintering temperature resulted in increased dielectric constant which is attributed to an increase in the grain size. Here we report an unusually high dielectric constant (24000 at −16 °C, 1 kHz) observed in PMN sintered at 1200 °C [PMN(1200)]. The room temperature dielectric constant and dissipation factor at 1 kHz is ~15000 and 0.0025, respectively, for PMN(1200). These values are superior to the reported values. A detailed and systematic study on phase, physical and dielectric properties and microstructure has been carried out. Grain size appears to be a dominant factor in controlling dielectric constant rather than the pyrochlore phase, as claimed earlier.

Electrical Conduction in 0–3 BaTiO3/PVDF Composites

(1-x)PVDF-xBaTiO3 ceramic-polymer composites with x = 0.10, 0.20, 0.30 were prepared using melt growth technique. The crystal symmetry, space group and unit cell dimensions were determined from the XRD data of BaTiO3 using FullProf software, whereas crystallite size and lattice strain were estimated through Williamson-Hall approach. The distribution of BaTiO3 particles in the PVDF matrix were examined using a scanning electron microscope. The correlated barrier hopping model has been applied to the ac conductivity data in order to ascertain the conduction mechanism of charge transport in BaTiO3/PVDF composites. Also, the ac conductivity data have been used to estimate the apparent activation energy, density of states at Fermi level and minimum hopping length. Filler concentration dependent ac conductivity, density of states at Fermi level and minimum hopping length data followed definite trends of exponential growth/decay types of variation.

Synthesis and transport properties of mixed MEEP-PEO-NaSCN polymer electrolytes

Abstract Poly[bis(methyoxy-ethoxy-ethoxy)phosphazene] (MEEP) has been prepared from hexachlorocyclotriphosphazene by polymerizing the latter and then replacing the Cl groups by methoxy ethoxy-ethoxy groups to obtain a completely amorphous polymer. Mixed electrolyte of MEEP, PEO and NaSCN have been prepared by varying NaSCN concentration in the electrolyte while maintaining the ratio of MEEP and PEO constant at 55:45. The mixed electrolytes showed the highest electrical conductivity of 5×10 −5 S cm −1 at room temperature which is two orders of magnitude higher than PEO-based systems. Mixed electrolytes have been characterized by infrared and differential scanning calorimetry. The transport numbers of Na + and SCN − are 0.92 and 0.08 respectively. Addition of PEO, to amorphous MEEP introduces crystalline PEO-NaSCN phases into the mixed electrolyte system.