Extrinsic and intrinsic structural change during heat treatment of polyaniline

HCl doped polyaniline (PAni) was synthesized electrochemically and heat treated at 150 °C, 200 °C and 250 °C for 30 min in vacuum. Different intrinsic and extrinsic structural changes due to heat treatment were determined from XRD, TGA, FT-IR, conductivity and solubility measurement. When HCl doped PAni is subjected to heat treatment, different changes are taking place in the system like doping, dedoping (extrinsic), oxidation, chain scission, cross-linking and changes in crystal structure (intrinsic). Mechanism for doping, dedoping, oxidation, chain scission and cross-linking is proposed.     

Computational analysis of ordering in non-liquid crystalline versus liquid crystalline materials with special reference to <Emphasis Type="Italic">n</Emphasis>BAC

A computational analysis of ordering in non-liquid crystalline p-n-alkyl benzoic acid, having 1 (1BAC), 2 (2BAC) and 3(3BAC) carbon atoms in the alkyl chain has been carried out with respect to translatory and orientational motions, but detailed results are reported only for 3BAC. The evaluation of net atomic charges and dipole moments at each atomic center has been carried out using complete neglect differential overlap (CNDO/2) method. The modified Rayleigh-Schrodinger perturbation theory along with the multicentered-multipole expansion method has been employed to evaluate long-range interactions, while a “6-exp” potential function has been assumed for short-range interactions. On the basis of stacking, in-plane and terminal interaction energy calculations, all possible arrangements of a molecular pair have been considered. A comparative picture of molecular parameters, such as total energy, binding energy, and total dipole moment of 3BAC with higher homologous series liquid crystalline compounds having 4(4BAC), 5(5BAC), and 6(6BAC) alkyl chain carbon atoms, has been given. It is found that, if a suitable functional group is attached to 3BAC, so that the length to breadth ratio is increased, the molecule will show a change in the long-range order, the phase transition temperature and other liquid crystalline properties.     

Dispersion tailoring in single mode optical fiber by doping silver nanoparticle

We propose an optical fiber which has very low dispersion loss (typically ~ 6.7 ps²/km at 1,550 nm) that can be achieved by doping Ag nanoparticle into the core glass. At low absorption loss approximation, dispersion free propagation can be achieved up to 64 km for a 20 ps pulse. Enhanced third order nonlinearity due to the presence of Ag nanoparticle (typically ~ 3.82 × 10^?20 W/m²) compensates for long length dispersion broadening that is not possible in conventional fused silica step index fiber.     

Incremental optimization in donor polymers for bulk heterojunction organic solar cells exhibiting high performance

The power conversion efficiency of an organic solar cell has now exceeded the 10% mark, which is a significant improvement in the last decade. This has been made possible due to the development of low-band-gap polymers with tunable electron affinity, ionization potential, solubility, and miscibility with the fullerene acceptor, and the improved understanding of the factors affecting the critical device parameters such as the V_OC and the J_SC. This review examines the latest strategies, results, and trends that have evolved in the design of solar cells with better efficiency and durability. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Spectral changes of stochastic beams scattered on a deterministic medium

It is well known that scattering of a polychromatic plane wave by a random medium, i.e., by a medium whose refractive index varies randomly with position, may produce frequency shifts of spectral lines. It has been a common perception that a random medium is required for generation of such spectral shifts by scattering. In this Letter we show that such a phenomenon occurs even when the refractive index of the medium is a deterministic function of position. We also show that this phenomenon may be used to obtain information about the structure of a deterministic medium.     

Ytterbium-sensitized thulium-doped fiber laser with a single-mode output operating at 1900-nm region

A single-mode laser is demonstrated using a newly developed double-clad thulium-ytterbium-doped fiber (TYDF) in a linear cavity formed by two fiber Bragg gratings (FBGs). The YTF used is drawn from a D-shape preform fabricated using the modified chemical vapor deposition and solution doping technique. The laser is operated at 1 901.6 nm via the transition of thulium ions from 3F4 to 3H6 with the assistance of ytterbium to thulium ion energy transfer. The efficiencies of the laser are 0.71% and 0.75% at 927- and 905-nm multimode pumping, respectively. The thresholds of the launched pump power for 927- and 905-nm pumping are 1 314 and 1 458 mW, respectively. A 7-mW output is obtained at a 905-nm pump power of 2 400 mW.     

Does a light beam of very narrow bandwidth always behave as a monochromatic beam?

We show by analyzing coherence and polarization properties of narrow-band stochastic electromagnetic beams that a light beam of a very narrow bandwidth does not necessarily behave as a monochromatic beam with regards to its coherence and polarization properties. Our analysis also provides a new insight into the relation between the theories of coherence and polarization in the space-time domain and in the space-frequency domain.     

Polypyrrole nanocomposite made by polypyrrole dispersion in poly (vinyl alcohol) matrix

Polypyrrole-polyvinyl alcohol (PPy-PVA) nanocomposite is synthesized by dispersing interface polymerized polypyrrole in PVA matrix. The composite films are characterized by FTIR, XRD and SEM. FTIR spectra indicates crosslinking in the composite film. XRD pictures show more crystallinity for higher polymerization temperature, whereas SEM pictures clearly indicate PPy rod formation for the same film. The electrical conductivity of the films is in the range of 10⁻¹ S/cm, whereas the current-voltage (I–V) characteristics shows power law behaviour.     

Effect of different reaction parameters on the conductivity and dielectric properties of polyaniline synthesized electrochemically and modeling of conductivity against reaction parameters through regression analysis

The polyaniline (PAni) is prepared electrochemically from an aqueous solution of aniline and HCl in a single compartment electrochemical cell. Different PAni samples obtained by varying monomer concentration, acid concentration, applied potential, reaction time, and reaction temperature are subjected to conductivity and dielectric tests. The degree of crystallinity, d‐spacing, interchain separation, and crystallite size are determined form X‐ray analysis, the oxidation state is determined from infrared spectroscopy (FTIR) analysis, and the doping level is estimated from TGA analysis for all the PAni samples synthesized under different conditions. All these structural properties are correlated with electrical properties. The whole result reveals that all the aforementioned reaction parameters affect the structural properties, which in turn affect the electrical properties of PAni. The mathematical model correlations between conductivity and reaction parameters are established from the regression analysis for individual variables as well as for all the variables together. These relationships give the conductivity as an output when we input the value of reaction variables. The output obtained from the model relations found in well agreement with the experimental results under identical conditions. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2046–2059, 2007