R.P. Pant

Improved microwave absorption in lightweight resin-based carbon foam by decorating with magnetic and dielectric nanoparticles

Carbon foams (CFoams) are sponge-like high performance lightweight engineering materials that possess excellent electrical and mechanical properties as well as thermal stability. CFoams possess bulk density in the range from 0.30 to 0.40 g cm−3 and open porosity of more than 70%. The CFoam consists of pore walls, i.e., ligaments, which are responsible for the conduction path and hence the electrical conductivity due to mobile charge carrier (delocalized π electron), are interconnected to each other. The high value of electrical conductivity causes the CFoam to act as an electromagnetic radiation reflector rather than an absorber; however, in certain applications, shielding materials must be able to absorb the maximum electromagnetic radiation. Therefore, to improve the absorptivity of electromagnetic radiation in lightweight CFoams, the CFoams are decorated by Fe3O4 and ZnO nanoparticles. It is observed that coating with Fe3O4 and Fe3O4–ZnO nanoparticles not only improved the absorption losses but also enhanced the compressive strength of CFoam by 100%. This modified CFoam demonstrated excellent shielding response in the frequency range from 8.2 to 12.4 GHz, in which the total shielding effectiveness (SE) was dominated by absorption losses. The total SE is −45.7 and −48.5 dB of Fe3O4 and Fe3O4–ZnO-coated CFoam, respectively, and it is governed by absorption losses of −34.3 dB and −41.5 dB, respectively. Moreover, the absorption losses increased by 236% in Fe3O4-coated CFoam and 281% in Fe3O4–ZnO-coated CFoam without much enhancement in the bulk density. This is due to the high level of magnetic and dielectric losses of nanoparticles with high surface area. Note that the absorption losses are 80% higher than any value reported for CFoam; thus, lightweight CFoam decorated with magnetic and dielectric nanoparticles is an excellent material for stealth technology.

Investigations on ferrofluid-conducting polymer composite and its application

The study describes the synthesis and characterization of ferrofluid-conducting polymer composite materials and its thin films. The results of our measurement for the film grown under the influence of with and without magnetic field are quite interesting and encouraging for the electromagnetic interference shielding purpose. Change in the physical properties were correlated by analyzing the spectral features of the films.

XRD, SEM, EPR and microwave investigations of ferrofluid-PVA composite films

Ferrofluid-polymer composite films, prepared under the influence of a magnetic field and without magnetic field, have been studied for their physical characteristics. Results of X-ray diffraction, electron paramagnetic resonance, surface structure and microwave absorption studies are reported in this paper and the experimental data correlated with the crystallite size and relatively cluster size variation in the applied field direction.

Improved properties of bidispersed magnetorheological fluids

We have investigated the influence of nanosized particle concentration on rheological properties when mixed with a magnetorheological (MR) fluid. We have also studied the structural, morphological and magnetic properties of ferrofluid-based MR fluids (F-MRFs). Field-induced rheological and viscoelastic properties of F-MRFs with varying shear rate and strain amplitude have been investigated. The Herschel–Bulkley model was found to fit well with the flow behaviour of F-MRFs. In the oscillatory strain sweep test, F-MRFs show linear viscoelasticity at low strain and the storage modulus (G′) is higher than the viscous modulus (G′′), which indicates the existence of strong links among the particles that form the microscopic structures. The storage modulus increases with increasing weight fraction of nanosized particles. Furthermore, the loss factor (ratio of G′′ and G′) was also investigated as a function of magnetic field strength. In addition, time-dependent relaxation behaviour of magnetically induced chain-like structures has also been described. The study reveals that the addition of nanoparticles to MR fluids increases the viscosity as well as the fluid stability under a magnetic field.

Investigation of dielectric behaviour in ferrofluid-ferroelectric liquid crystal nanocomposites

We demonstrate here the frequency-bias-temperature-dependent dielectric studies of ferrofluid (FF) mixed ferroelectric liquid crystals (FLCs; SCE13 and Felix017/100). As a FF, cobalt ferrite nanoparticles (∼9 nm) synthesised through chemical co-precipitation were used in the study. In these FF–FLCs nanocomposites, a memory (dielectric) effect is observed at room temperature, which becomes more pronounced as the temperature tends towards the smectic C* (SmC*) to smectic A (SmA) phase transitions. Moreover, in addition to the memory effect, the observed enhanced dielectric constant (ϵ′) also reveals the importance of FF nanoparticles in the FLC matrix. We anticipate that, in current nanocomposites, the interaction of the AC field frequency response of FF nanoparticles with the dielectric response of FLCs could be the plausible reason for these observations.

Preparation and characterization of magnetic polymeric thin films

The revolution in information technology has led the scientists to look for advanced materials to cater for the growing capacity of data storage. Over the recent years, significant advances have been made in the development of materials, which possess smart and intelligent functions of the magnetic data storage and handling. These magnetic materials exhibit ferroelectric, ferrielectric and anti-ferroelectric properties. There have been successful attempts to prepare semiconducting conjugated polymers as potential materials, which has potential of being used as a base material. The magnetic properties of polyaniline are achieved by suitably doping the base material. We have developed a unique and novel method for preparation of polyaniline magnetic thin films by vapor deposition of magnetic polyaniline powder on various substrates. The characterization of thin films by optical absorption, SEM, X-ray are reported here. These studies suggest that vacuum deposited magnetic polyaniline thin films are suitable for magnetic data storage device fabrication.

Kinetic, mechanistic, and thermodynamic investigations on ferrofluid-catalyzed oxidation of L-ascorbic acid by hydrogen peroxide in acidic aqueous solution

The reduction of ferrofluid (FF) by L-ascorbic acid (H(2)A) and the reoxidation of the reduced FF to its original form by hydrogen peroxide have been investigated in aqueous acidic medium. The rate of reduction of FF was found to be first order with respect to [H(2)A] and [FF] and independent with respect to [H(2)O(2)] and ionic strength. The rate of reduction of FF increased with increasing pH (2.5-4.0), having an inverse first order dependence in [H(+)]. With increasing temperature (15-45 degrees C), the rate of reduction was increased in line with the Arrhenius equation. Based on experimental evidence and results a mechanism, operative to reduce FF and reoxidize the reduced FF by H(2)O(2), which makes the system catalytic, is suggested. Thermodynamic quantities associated with FF-catalyzed oxidation of H(2)A by H(2)O(2) were determined and compared with other closely related systems.

Variable temperature electron paramagnetic resonance investigations of a kerosene-based magnetic fluid

Abstract The kerosene-based ferrofluid RP-90 has been examined by electron paramagnetic resonance (EPR) from room temperature to liquid nitrogen temperature at the X-band frequency 9.41 GHz. The variations in the g -value and ( ΔH ) with temperature indicate the presence of a magnetic phase transition from a ferromagnetic to a ‘spin glass or cluster glass’ state. This transition is associated with the freezing point of the carrier medium. No evidence of the presence of superparamagnetism was observed. The linewidth variation with temperature indicates a dominant bulk rotation relaxation mechanism ( τ B ).

Effect of CoFe magnetic nanoparticles on the hole transport in poly(2-methoxy, 5-(2-ethylhexiloxy) 1,4-phenylenevinylene)

The effect of doping of CoFe magnetic nanoparticles (MNPs) on the hole transport in poly(2-methoxy,5-(2-ethylhexyloxy)-1,4-phenylenevinylene)(MEH-PPV) thin films has been investigated in the temperature range 280?120?K. Hole transport in MEH-PPV is found to be governed by space-charge-limited-conduction (SCLC) with exponential distribution of traps in energy space. Doping of CoFe MNPs in MEH-PPV reduces the hole mobility from 1 ? 10?5 to 6 ? 10?6?cm2?V?1?s?1 by introducing new trap sites causing their net density increase from 1 ? 1018 to 2.1 ? 1018?cm?3, which is likely to result in balanced injection and efficient recombination of charge carriers to improve the performance of polymer light emitting diodes.

INVESTIGATIONS ON NANOCRYSTALLINE SUPERPARAMAGNETIC PARTICLES OF CoFe2O4

Superparamagnetic (SP) crystalline cobalt ferrite (CoFe2O4) nanoparticles are synthesized by chemical co-precipitation method. Grown nanoparticles are annealed in air at various temperatures in the range 373 K to 1173 K to understand the variation in properties in nanoregion. Physical properties are analyzed for crystalline phase, crystallite size, particle size, shape, magnetization and relaxation behavior by using various characterization techniques viz. X-ray diffractometer (XRD), transmission electron microscope (TEM), vibrating sample magnetometer (VSM) and electron paramagnetic resonance (EPR). Annealing effect on various physical properties of particles are investigated. Particles are used in the development of stable ferrofluid.