Anjan Ray

Polyaniline: Solutions, Films and Oxidation State

Abstract The emeraldine oxidation state of polyaniline in its base form, “emeraldine base” can be solution-processed to yield large flexible films which can be doped to the metallic conducting regime (σ ∼ 1-5 S/cm). The approximate solubility of emeraldine base at room temperature in 80% aqueous acetic acid, 60% and 88% aqueous formic acid, dimethyl sulfoxide (DMSO), dimethylformamide (DMF) and N-methylpyrrolidinone (NMP) have been determined. Both emeraldine base and emeraldine hydrochloride can be sublimed onto a variety of substrates to produce high quality, ∼2000 A thick films which are similar but not identical to emeraldine base. Emeraldine base, which is slowly oxidized by air, can be reconverted to the emeraldine oxidation state by treatment with dilute aqueous acids.

Polyaniline: Processability from aqueous solutions and effect of water vapor on conductivity

Abstract The chemically-synthesized emeraldine base form of polyaniline is soluble in aqueous acetic acid solutions, in which it presumably exists as the ‘doped’ emeraldine acetate salt. Films having a conductivity of ≈0.5 –2 S /cm may be cast from the solutions. These films may be converted to relatively flexible, free-standing, lustrous, copper-colored films of emeraldine base, which can in turn be converted to free-standing, lustrous, dark blue films of emeraldine hydrochloride ( θ ≈1–2 S / cm ). The resistance of films of both emeraldine base and 50% protonated emeraldine hydrochloride decreases by a factor of ∼2 when exposed to ∼4 Torr of water vapor. The resistance increases only very slowly on removing the water vapor under dynamic vacuum, consistent with the postulated structure of emeraldine hydrochloride involving ‘islands’ of heavily-doped emeraldine base in a matrix of undoped or slightly-doped material.

Polyaniline: Doping, structure and derivatives

Abstract Redox titration results and electronic spectral evidence show that the oxidation state of the “emeraldine” base form of polyaniline can vary depending on whether its synthesis is performed in the presence or absence of air. Chemical doping of leucoemeraldine, the completely reduced form of polyaniline, to selected oxidation states can be accomplished by a variety of oxidizing agents such as Cl 2 , (NO) + (PF 6 ) − , FeCl 3 , SnCl 4 and TCNQ.

Polyaniline: protonation/deprotonation of amine and imine sites

Abstract A model describing the dependence of the protonation level and the oxidation potential of polyaniline as a function of pH of equilibration and oxidation state has been derived. It is assumed that amine and imine sites do not function independently. Predictions are compared with previous experimental data.

Solution studies of the emeraldine oxidation state of polyaniline

Abstract Optical studies of emeraldine base in solutions show a red shift in both 2eV and 3.8eV absorption peaks compared with the optical absorption for emeraldine films and powders. As for solids, the 2.0eV peak is absent for the salt form. Unlike the salt film, the strong absorption peak is narrow without the free electron absorption tail, suggestive of strong localization of polarons in the solution form. Dilution studies show there is no shift in the absorption peaks with concentration in both emeraldine base and salt, indicating that optical absorption is an intrachain interaction. Temperature dependent UV-VIS spectra show the first thermochromatic effect in a system without side groups that suggests possible ring flipping. Photoinduced optical studies of emeraldine base polymer in solution shows photoinduced absorption peaks at 1.4eV and 3.0eV and photoinduced bleaching at 1.8eV. The photoinduced absorption peak observed at 0.9eV in film is no longer present. Its disappearance implies the importance of interchain interactions for the formation of the electronic state. In contrast, the 1.4eV absorption is from the interchain excitation of polarons.

X-ray structure of polyanilines

Abstract We describe two classes of the emeraldine form of polyaniline, Class I exhibits ES-I crystal structure in the HCl salt form and in the base form it is amorphous EB-I. Class II materials form partially crystalline structures EB-II and ES-II in base and HCl salt forms, respectively. We compare structural results on emeraldine with data for partially crystalline leucoemeraldine base (LEB) and pernigraniline base (PNB) — the fully reduced and oxidized forms of polyaniline, respectively. We contrast our studies of the EB-I/ES-I system with results for poly( o -toluidine) base, POT-EB and hydrochloride, POT-ES.

Influence of Burner Geometry on Heat Transfer Characteristics of Methane/Air Flame Impinging on Flat Surface

An experimental study has been conducted to find the heat transfer characteristics of methane/air flames impinging normally to a flat surface using different burner geometries. The burners used were of nozzle, tube, and orifice type each with a diameter of 10 mm. Due to different exit velocity profiles, the flame structures were different in each case. Because of nearly flat velocity profile, the flame spread was more in case of orifice and nozzle burners as compared to tube burner. Effects of varying the value of Reynolds number (600–2500), equivalence ratio (0.8–1.5) and dimensionless separation distance (0.7–8) on heat transfer characteristics on the flat plate have been investigated for the tube burner. Different flame shapes were observed for different impingement conditions. It has been observed that the heat transfer characteristics were intimately related to flame shapes. Heat transfer characteristics were discussed for the cases when the flame inner reaction cone was far away, just touched, and was intercepted by the plate. Negative heat fluxes at the stagnation point were observed when the inner reaction cone was intercepted by the plate due to impingement of cool un-burnt mixture directly on the surface. Different heat transfer characteristics were observed for different burner geometries with similar operating conditions. In case of tube burner, the maximum heat flux is around the stagnation point and decay is faster in the radial direction. In case of nozzle and orifice burner, the heat transfer distribution is more uniform over the surface.

15N NMR of polyaniline

Abstract 15 N NMR spectroscopy has been utilized as a structural probe for the leuco- and “emeraldine” base forms of polyaniline. Preliminary results suggest that the emeraldine base polymer exists as an alternating copolymer of oxidized and reduced units. End-groups are not detected at the experimental level of sensitivity.

Development of a semi-empirical model for pyrolysis of an annular sawdust bed

Abstract A model for simulating pyrolysis of sawdust in a packed bed of annular shape has been developed. Heat transfer is assumed to be purely due to conduction, and chemical reaction of pyrolysis has been approximated to a pseudo-first order reaction. The reaction rate constant has been obtained as a function of temperature for the species of sawdust used in the present work using thermogravimetric analysis, and its variation with heating rate has been accounted for. Thermal conductivity of the packed bed of sawdust has been estimated experimentally by temperature measurement in the sawdust bed. The sawdust bed was pyrolysed using an electric heater in contact with the inner surface of the annulus as the source of energy. Using the history of temperature profiles measured on the heater wall at various points of time, a simulation of the experiment has been carried out. The predicted mass loss history compares reasonably well with the measured one. A sensitivity analysis using the model suggests that the predictions may be improved by considering the flow of volatiles in the void space of char bed, and by accounting for secondary pyrolysis due to residence of volatiles in the bed.

Use of CFD simulation as a design tool for biomass stoves

Design of biomass stoves has relied mostly on empirical information and trial-and-error experiments backed up by simple thermodynamic and heat transfer calculations. Quite frequently, the details of fluid flow inside the biomass stove, which is caused by buoyancy due to the high temperature prevailing in the combustion region, have been ignored and correlations of heat transfer based on forced flow have been used in the heat transfer analysis of stoves. This paper presents an approach in which detailed CFD simulations of the flow, heat transfer, pyrolysis and combustion in th e configuration of a simple sawdust stove are used to evolve simple algebraic equations that describe individual phenomena. Such equations are needed in the field for performance analysis and prediction, and could also be used for the optimization of stove geometry for performance. The paper describes the development of the building-blocks of the detailed simulation model and its use in the derivation of simple model equations relating design and performance parameters.