Manju Arora

High permittivity polyaniline–barium titanate nanocomposites with excellent electromagnetic interference shielding response

Organic conductive polymers are at the forefront of materials science research because of their diverse applications built around their interesting and unique properties. This work reports for the first time a correlation between the structural, electrical, and electromagnetic properties of polyaniline (PANI)-tetragonal BaTiO3 (TBT) nanocomposites prepared by in-situ emulsion polymerization. XRD studies and HRTEM micrographs of these nanocomposites clearly revealed the incorporation of TBT nanoparticles in the conducting PANI matrix. EPR and XPS measurements reveal that increase in loading level of BaTiO3 results in a reduction of the doping level of PANI. The Ku-Band (12.4-18 GHz) network analysis of these composites shows exceptional microwave shielding response with absorption dominated total shielding effectiveness (SET) value of -71.5 dB (blockage of more than 99.99999% of incident radiation) which is the highest value reported in the literature. Such a high attenuation level, which critically depends on the fraction of BaTiO3 is attributed to optimized dielectric and electrical attributes. This demonstrates the possibility of using these materials in stealth technology and for making futuristic radar absorbing materials (RAMs).

Microwave Absorption and EMI Shielding Behavior of Nanocomposites Based on Intrinsically Conducting Polymers, Graphene and Carbon Nanotubes

© 2012 Saini and Arora, licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Microwave Absorption and EMI Shielding Behavior of Nanocomposites Based on Intrinsically Conducting Polymers, Graphene and Carbon Nanotubes

Formation mechanism, electronic properties & microwave shielding by nano-structured polyanilines prepared by template free route using surfactant dopants

Conducting polymers are at the forefront of nanomaterials research but the fundamental mechanisms that govern the formation of functional nanostructures and control their electromagnetic (EM) properties are still unknown. Herein, we report for the first time a detailed correlation between acquired morphology, structural, spectral, electrical and EM properties of the polyaniline (PANI) nanostructures synthesized by a template free route using surfactant dopants as structure directing agents. Aniline has been emulsion polymerized in the presence of different sulfonic acids viz. dodecylbenzenesulfonic acid, camphorsulfonic acid, ligninsulfonic acid & cardanolazophenylsulfonic acid and the formed PANIs have been designated as PDB, PCS, PLS and PCD, respectively. The SEM investigations revealed that the morphology is critically dependent on the nature of the dopant, while FTIR, XRD, EPR and UV-visible studies revealed that doping level follows the order PCD 99.999% of incident EM radiation) demonstrate the potential of these materials for making future microwave shields.

An investigation on the key features of a D–π–A type novel chalcone derivative for opto-electronic applications

The current study is focused on the donor–bridge–acceptor (D–π–A) type of novel organic charge transport and non-linear optical material, 1-(4-bromophenyl)-3-(2,4,5-trimethoxyphenyl) prop-2-en-1-one (2,4,5-TMBC) to spotlight its various important properties through experimental and quantum chemical approaches. The compound 2,4,5-TMBC was synthesized via a Claisen–Schmidt condensation reaction and its single crystal was grown by a slow evaporation solution growth technique. FT-IR and FT-Raman spectra of 2,4,5-TMBC were obtained and investigated. The molecular geometry of 2,4,5-TMBC was optimized by HF, B3LYP, CAM-B3LYP, wb97xd and LC-BLYP methods using the 6-31G* basis set. The calculated geometrical parameters and vibrational spectra are in good agreement with the experimental results. Time dependent density functional theory (TD-DFT) has been applied to investigate the optical properties of the title compound. The absorption wavelength calculated at the TD-B3LYP/6-31G* level of theory in the gas phase was in good agreement with the experimental value (∼400 nm) when compared with other methods. The HOMO–LUMO energy gap was calculated at all the applied levels of theory. The total dipole moment, polarizability, anisotropy of polarizability and static first and total hyperpolarizability values of 2,4,5-TMBC were calculated at different levels of theory. The dipole moment and first hyperpolarizability values are found to be many folds (2 and 56 times calculated at B3LYP) higher than urea. It is also expected that 2,4,5-TMBC would be electron transport material due to its smaller electron reorganization energy value. The study of non-linear optical (NLO) properties shows that 2,4,5-TMBC would be an outstanding candidate for NLO device applications.

Multiphonon infrared absorption in silicon

Investigations have been carried out on silicon crystals, grown by float zone (FZ) and Czochralski (CZ) methods, of infrared absorption bands using a Fourier transform infrared spectrophotometer. Multiphonon bands are identified in the light of recent theoretical calculations based on the total energy of silicon crystal lattice. Theoretical results of Ihm et al.(1) and Yin and Cohen(2,3) are found to be in good agreement with the experimental observations of multiphonon infrared bands.

Photoluminescence and electron paramagnetic resonance studies of springlike carbon nanofibers

Carbon nanofiber (CNF) with springlike and double-helix structures has been synthesized by catalytic thermal pyrolysis of an acetylene precursor at 850–950 °C using iron nanopowder and thiophene as catalyst and promoter, respectively. High resolution electron microscopy revealed a higher d-spacing (∼3.46 A) of (002) crystal plane than customary multiwalled carbon nanotube (MWCNT) (3.37 A) that helps in sustaining mechanical shocks better than MWCNTs. The large surface to volume ratio of springlike CNF does provide many delocalized free electrons to enhance the photoluminescence activity. Electron paramagnetic resonance signal showed a single narrow line having g-value 2.0024±0.0002 and spin contribution 3.4956×10−16 spins/g.

Influence of ZnO on optical properties and dc conductivity of vanadyl-doped alkali bismuthate glasses

A new family of glasses based on Bi2O3 was found in the systems xZnO · (0.30 − x)M2O · 0.70Bi2O3 (M = Li, Na) in the range 0.00 ≤ x ≤ 0.20 containing 2.0 mol% of V2O5. Density, molar volume, optical band gap and dc conductivity of these glasses have been investigated. The position of the absorption edge and hence the value of the optical band gap has been reported.

Mechanism of photoluminescence enhancement and quenching in Nd2O3 nanoparticles–ferroelectric liquid crystal nanocomposites

The mechanism of photoluminescence enhancement and quenching in np-Nd2O3:FLC nanocomposites has been explored in the current study by UV-Vis and photoluminescence (PL) spectroscopy techniques. UV-Vis absorption spectra of Nd2O3 NPs in the 200–800 nm range shows two absorptions at 248 nm and 292 nm whereas pure FLC gives a broad absorption in the 265 nm to 348 nm region. PL emission intensity of np-Nd2O3:FLC composites recorded at 248 nm excitation wavelength where Nd2O3 NPs show intense emission, increases with gradually increasing the concentration of NPs up to 8 μl. This enhancement in PL intensity without blue/red shifting the FLCs emission band was attributed to the up-conversion of doped Nd3+ ions and transfer of excitation energy to liquid crystal molecules. When excited with 248 nm, the Nd3+ ground state 4I9/2 absorption excites electrons to a higher excited state 2G5/2. The excited Nd3+ ions in 2G5/2 level relax non-radiatively to the metastable 2H11/2 state and then re-excites to an unstable 4G11/2 level. The electrons populated in 4G11/2 release energy either radiatively to different defect energy levels in the visible region or transfers this excitation energy to liquid crystal molecules which resulted into the enhancement in PL emission intensity. On the other hand, emission spectra at 303, 323, 333, 343 nm excitation wavelengths exhibit quenching of all emission bands in np-Nd2O3:FLC composites due to the stress induced structural disordering by the Nd2O3 NPs in the FLC matrix and creation of non-radiative channels in the system.

Electro-optic switching in iron oxide nanoparticle embedded paramagnetic chiral liquid crystal via magneto-electric coupling

The variation in optical texture, electro-optic, and dielectric properties of iron oxide nanoparticles (NPs) embedded ferroelectric liquid crystal (FLC) with respect to change in temperature and electrical bias conditions are demonstrated in the current investigations. Improvement in spontaneous polarization and response time in nanocomposites has been attributed to magneto-electric (ME) coupling resulting from the strong interaction among the ferromagnetic nanoparticles exchange field (due to unpaired e−) and the field of liquid crystal molecular director. Electron paramagnetic resonance spectrum of FLC material gives a broad resonance signal with superimposed components indicating the presence of a source of spin. This paramagnetic behavior of host FLC material had been a major factor in strengthening the guest host interaction by giving an additional possibility of (a) spin-spin interaction and (b) interactions between magnetic-dipole and electric-dipole moments (ME effects) in the composite materials...

Evolution of excitation wavelength dependent photoluminescence in nano-CeO2 dispersed ferroelectric liquid crystals

The optical properties of nano-ceria (nano-CeO2) dispersed ferroelectric liquid crystals (FLCs) have been investigated by excitation wavelength dependent photoluminescence (PL) spectroscopy. The PL spectra of nano-ceria exhibited a strong excitation wavelength dependence in the 255–370 nm range. The red shift in the violet emission band of ceria i.e. from 368 nm to 396 nm with increasing excitation wavelength, has been attributed to the recombination of electrons trapped in the defect band and the deeply trapped holes in oxygen vacancies. This excitation wavelength dependence of ceria has noticeably been manifested in the PL response of FLC–CeO2 nanocomposites as well. PL emission recorded at an excitation wavelength where host and guest materials show intense emission, i.e. 340 nm, exhibits a quenching effect connected to the overlapping of emission and absorption bands of the host FLC and guest ceria NPs respectively. No blue/red shift in the spectral energy band was observed at 310 and 340 nm excitations. On the other hand, emission spectra at a lower excitation wavelength followed a reverse trend: an increase in the emission intensity, with a large blue shift in spectral energy band. The mechanisms involved in the changes of the PL spectrum of FLC–ceria nanocomposites with varying ceria concentration and excitation wavelengths are discussed in detail.