Electrical transport and magnetoresistance in advanced polyaniline nanostructures and nanocomposites

In this paper, the electrical transport mechanism and giant magnetoresistance (GMR) in advanced polyaniline (PANI) nanostructures and the related PANI nanocomposite systems are critically reviewed. The GMR phenomena in these materials have been theoretically interpreted by numerical models including forward interference model and wave-function shrinkage model. This knowledge could serve as a guideline for optimal design and manufacturing of conductive polyaniline-based GMR devices.     

Electrical transport properties in zirconia/alumina functionally graded materials

Functionally graded materials (FGMs) are promising candidates for the fabrication of technological components, not only as structural devices, but also in electrochemical ones, such as solid oxide fuel cells (SOFC), or high-efficiency hybrid direct energy conversion systems. In the present work FGMs were prepared by the sequential slip casting technique, starting with an yttria tetragonal zirconia polycrystalline layer and increasing subsequently the amount of Al₂O₃ in the following layers. Electrochemical impedance spectroscopy (EIS) analysis was used to evaluate the electrical characteristics of these materials and to compare with those of the monolithic compacts. In general, it was observed that the FGM conductivity is ruled by the conductivity of the layer which contains the highest amount of alumina blocking particles. By EIS no electrical interfaces between adjoining layers were detected and, accordingly, no specific electric ohmic losses were observed. The conductivity of the FGMs is close to that calculated using the normalized thicknesses and the alumina volume fractions of the layers after measuring the conductivity of the monolithic materials with the same composition to what correspond to that of the final layer in the FGM. These results suggest that the gradient structure can be used to control the oxygen vacancy motion, and then applied in electrochemical devices.     

Electrical transport and morphological studies of polyaniline nanostructures

Polyaniline nanostructures have been synthesized by self‐assembly method by varying the dopant to monomer molar ratio. High resolution transmission electron micrographs show how the dopant to monomer molar ratio influences on the morphology and structure. The temperature dependence of dc conductivity study shows semiconducting behavior. From dc conductivity study it has been observed that conductivity increases with increasing dopant concentration and maximum conductivity is attained at dopant to monomer molar ratio of 3:4. From the slope of the reduced activation energy versus temperature plot it is confirmed that the charge transport in polyaniline nanostructures is in insulating regime and dominated by variable range hopping mechanism. In particular, a crossover from 1D to 3D variable range hopping conduction is observed by changing the dopant to monomer molar ratio. With increasing the dopant concentration the 680 nm absorption peak shifted towards higher wavelength range. The red shifting of this peak indicates the increased extent of π‐conjugation length. The enhancement of characteristic band intensity at 1336 cm^?1 in Micro‐Raman spectra indicates the increase of delocalization degree. Temperature profiles of the degradation processes have been mapped using thermogravimetry analyzer and it is observed three‐step weight losses for all the samples. POLYM. ENG. SCI., 55:995–1002, 2015. © 2014 Society of Plastics Engineers     

The transport properties of oxygen in aqueous borate solutions

The solubility and diffusivity of oxygen in borate buffer solutions were studied on a Pt μ electrode under diffusion-controlled conditions. The solubility of oxygen in diluted borate solution is unusually high (4.2 × 10⁻³ M l⁻¹), whereas its diffusion coefficient is lower (5 × 10⁻⁶ cm² s⁻¹) than in other aqueous solutions The decrease in oxygen solubility at higher ionic strengths is due to the salting-out effect. The results are consistent with the formation of “oxygen-borate” complex whereby the stability of BO₃ containing polymeric anions is enhanced.     

Preparation of surface initiated polystyrenesulfonate films and PEDOT doped by the films

Various substrates such as glass slides and silicon wafers were modified by styrylethyltrimethoxysilane to attach double bonds to those surfaces. The double bond layer was initiated and capped by benzoyl peroxide (BPO) and 2,2,6,6-tetramethylpiperidirooxy (TEMPO), respectively, to form ‘living’ free radical layer from which polystyrene brushes were grown. The density of double bonds on the surface controlled the orientation of polystyrene brush or film. The polystyrene films were then sulfonated by fuming sulfuric acid (H₂SO₄·xSO₃) to obtain polystyrenesulfonic acid (PSS) films with controlled polymer chain alignment. The lower double bond density led to a lower degree of polymer chain alignment. 3,4-Ethylenedioxythiophene monomer was diffused into PSS film and then polymerized. A conductive polyethylenedioxythiophene (PEDOT)/PSS film was obtained. The films were characterized by four-point probe, AFM and UV-VIS. The conductivity of PSS/PEDOT film measured along the direction which is normal to polymer chain alignment, is lower than that from commercial PSS/PEDOT.     

Analytical solutions of moisture-chloride ion coupled transport in unsaturated concrete

Studies of chloride-induced corrosion in reinforced concrete structures are performed based on the reliable predictions of chloride and moisture distributions in concrete. This paper adopted the Laplace Transformation and the inverse Laplace Transformation to obtain the analytical solutions of the moisture-chloride two-way coupled transport processes. Additionally, the model has involved with realistic material parameters to predict the internal distributions of relative humidity and free chloride ions in concrete samples. To illustrate the accuracy of the present model, the calculations were compared with the available experimental results, and good agreements were obtained. It indicates that the present analytical model can successfully characterize the two-way coupling effects between chloride transport and moisture diffusion in concrete; and the model can provide the distribution profiles of both chloride and relative humidity in concrete, which are useful for predicting the service life of reinforced concrete structures.     

Useful representations of series solutions for transport problems

Simple techniques are presented for rearrangement of an infinite series in a systematic way such that the convergence of the resulting expression is accelerated. These procedures also allow calculation of required boundary derivatives. Several examples of conduction and diffusion-reaction problems illustrate the methods.     

Electrical and thermal transport behaviours of high-entropy perovskite thermoelectric oxides

Oxide-based ceramics could be promising thermoelectric materials because of their thermal and chemical stability at high temperature.However,their mediocre electrical conductivity or high thermal conductivity is still a challenge for the use in commercial devices.Here,we report significantly suppressed thermal conductivity in SrTiO₃-based thermoelectric ceramics via high-entropy strategy for the first time,and optimized electrical conductivity by defect engineering.In high-entropy(Ca_0.2Sr_0.2Ba_0.2Pb_0.2La_0.2)TiO₃bulks,the minimum thermal conductivity can be 1.17 W/(m·K)at 923 K,which should be ascribed to the large lattice distortion and the huge mass fluctuation effect.The power factor can reach about 295μW/(m·K²)by inducing oxygen vacancies.Finally,the ZT value of 0.2 can be realized at 873 K in this bulk sample.This approach proposed a new concept of high entropy into thermoelectric oxides,which could be generalized for designing high-performance thermoelectric oxides with low thermal conductivity.     

Electrical transport and magnetic properties of PEDOT‐ferrite nanocomposites

We have studied the temperature‐dependent transport and magnetic properties of the nanocomposites, containing varied amounts of CoFe₂O₄, NiFe₂O₄, and Fe₃O₄ nanoparticles embedded in the conducting poly(3,4‐ethylenedioxythiophene) or PEDOT matrix, in the temperature range 77–300 K. Resistivities of all the composites, including pure PEDOT follows the Mott VRH relation ρ = ρ₀ T^−1/4 over the studied temperature range. This suggests that hopping is the mechanism of transport in these systems. Plots of (lnρ − lnρ₀)/A as a function of temperature for all the studied samples are found to collapse on a single curve. Although, the conduction mechanism does not change with nanoparticle inclusions in the polymer matrix, the hopping parameters change in the nanocomposites. Magnetic studies of ferrite nanoparticles and nanocomposites show signature of superparamagnetic blocking, with a distribution of particle size. The spin structure on the surface of any particle is different from that of the core. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Vinyl polymerization, 399. Polymerization of methyl methacrylate with sodium polystyrenesulfonate in presence of polyethyleneglycol

The effect of polyethyleneglycol on the radical polymerization of methyl methacrylate initiated with an aqueous solution of sodium polystyrenesulfonate was studied. Under the definite condition, the conversion of methyl methacrylate raised from 6.6 to 100% by the addition of polyethyleneglycol. It was concluded that polyethyleneglycol acted only as a host of Na⁺, but not as a phase transfer catalyst.     

Electrical transport properties of Sm-doped La0.7Ca0.3MnO3 polycrystalline ceramics

Improving the magnetoresistance effect of perovskite ceramic materials under a low applied magnetic field to expand its application range is one of the main research directions of this type of material. In this study, La_0.7Ca_0.3MnO₃ was doped with different levels of Sm by the sol-gel method to yield a series of La_0.7-xSm_xCa_0.3MnO₃ (LSCMO) polycrystalline ceramics. X-ray diffraction (XRD) results revealed that LSCMO ceramics possessed standard perovskite structures. Scanning electron microscopy (SEM) showed grains closely connected without obvious holes. In addition, the grain size gradually decreased with the increase in Sm doping content. The resistivity temperature curves displayed a clear metal-insulator transition behavior of LSCMO accompanied by a steep change from ferromagnetic to paramagnetic behavior (FM-PM). The metal-insulator transition temperature (T_p) values of the as-obtained LSCMO gradually shifted toward lower temperatures with increase in Sm content. Moreover, resistivity temperature coefficient (TCR) and magnetoresistance (MR) values also gradually increased with Sm doping content. The transport properties in polycrystalline ceramics could be adequately explained by the double exchange model, which would be useful for interpreting the CMR effects when used in magnetic devices.     

Electrical transport properties of polycrystalline CVD graphene on SiO2/Si substrate

Transport behavior of single layer graphene (SLG) grown by chemical vapor deposition technique on copper foil and transferred to SiO₂/Si substrate has been studied by measuring the dc conductivity and Hall mobility in the temperature range 2–460 K. The samples of size 1 × 1 cm² have been found to be polycrystalline in nature. Raman spectrum has been studied at various locations of the sample and the formation of SLG has been confirmed. From dc conductivity and mobility measurements it has been concluded that the one dimensional grain boundary defects are mainly responsible for the deterioration of mobility and conductivity of charge carriers in the polycrystalline samples.     

The effect of weak acids upon the transport of carbon dioxide in alkaline solutions

The transport of carbon dioxide through stationary alkaline liquid films is investigated both theoretically and experimentally. Attention is focused on the effect of catalysis of the hydrolysis reaction and on the role of weak acids which may be present. As a result of their ionic character and their buffering capabilities, weak acids can substantially increase the rate of transport. The experimental magnitude of this effect, which has apparently not been generally recognized, is in good quantitative agreement with theoretical prediction.     

Water transport during the concentration of waste zinc sulfate solutions by electrodialysis

Electrodialysis is a useful electromembrane process for the purification or the demineralization of a wide variety of electrolytic solutions. It is also used for the concentration of sea water and for the reconcentration of dilute solutions in surface treatment works or in hydrometallurgical plants. In the last two particular cases, ED allows recycling of inorganic ions to the process stream and reuse of water, avoiding the discharge of dilute solutions as wastes in the environment.These both possibilities indicate that electrodialysis is a separation process of great interest. However, when used for concentrating aqueous solutions, there is always water transport from the diluting stream to the concentrating solution.It is often stated that this water transport is induced by the water of hydration of ions migrating from the diluting solution to the concentrating solution. Sometimes, the electroosmosis flow is also taken into account.The work presented here relates this water transport in the frame of the thermodynamics of irreversible processes. It starts with phenomenological relations between flux densities of water and ions from the diluting stream to the concentrating one and isothermal generalized forces. These forces are taken under the form of a gradient of the electrochemical potential. But, as they cannot be directly measured, the intensive variables really acting on water and ions are expressed as functions of practically measurable parameters. The flux of water is expressed taking into account the water associated with migrating ions, but it is not necessary to know the true hydration number of each ion, the value of which is generally unknown.In conclusion, flux densities are related to measurable forces by means of six parameters, quite different from classical phenomenological coefficients.Then, these equations are used to study water transport and ionic fluxes encountered during the concentration by electrodialysis of waste zinc sulfate solutions. The theoretical model suggested fits well experimental results obtained with two kind of electrodialysis stacks : one with tortuous path gaskets, the other with flow sheet spacers.As a result, this work shows that it is possible to define the appropriate parameters to be controlled during an electrodialysis process, and to predict correctly the effects of their variations.     

Electrical transport properties of small diameter single-walled carbon nanotubes aligned on ST-cut quartz substrates

A method is introduced to isolate and measure the electrical transport properties of individual single-walled carbon nanotubes (SWNTs) aligned on an ST-cut quartz, from room temperature down to 2 K. The diameter and chirality of the measured SWNTs are accurately defined from Raman spectroscopy and atomic force microscopy (AFM). A significant up-shift in the G-band of the resonance Raman spectra of the SWNTs is observed, which increases with increasing SWNTs diameter, and indicates a strong interaction with the quartz substrate. A semiconducting SWNT, with diameter 0.84 nm, shows Tomonaga-Luttinger liquid and Coulomb blockade behaviors at low temperatures. Another semiconducting SWNT, with a thinner diameter of 0.68 nm, exhibits a transition from the semiconducting state to an insulating state at low temperatures. These results elucidate some of the electrical properties of SWNTs in this unique configuration and help pave the way towards prospective device applications.     

Analytical solutions for species transport in a T‐sensor at low peclet numbers

A 3D analytical solution is presented for the problem of mass transport in a T‐sensor by taking the axial diffusion effects into account. The solution methodology is based on an eigenfunction expansion of the solute concentration and enjoys the variational calculus for the solution of the associated eigenvalue problem. The method is capable of handling a mixed electroosmotic and pressure‐driven velocity profile and is executed assuming a rectangular channel cross‐section although it can be easily extended to more complex geometries. Two simplified models, one based on a uniform velocity profile, valid for the channel half height to Debye length ratios of above 100, and the other based on a depthwise averaging of the species concentration to be used for cases in which the channel width to height ratio is above 5 are also presented. As a part of the latter, expressions are derived for the Taylor dispersion coefficient of the mixed flow in a slit microconduit. The most interesting finding of this study is that, when the diffusion mechanism significantly contributes to the axial movement of the species, the well‐known heterogeneous mass transport evolves into a nearly uniform pattern in the depthwise direction and the mixing length noticeably increases. © 2016 American Institute of Chemical Engineers AIChE J, 62: 4119–4130, 2016     

Heat transport in the membrane-electrode assembly of a direct methanol fuel cell: Exact solutions

We develop a model of heat transport in the membrane-electrode assembly of a DMFC. The exact analytical solutions to model equations are derived. Based on these solutions a method for measuring thermal conductivities of the catalyst layers and membrane in a fuel cell environment is suggested.     

Mass transport studies at rotating cylinder electrode during zinc removal from dilute solutions

The mass transport in the rotating cylinder electrode (RCE) for the Zn(II) recovery from dilute solutions was investigated. Global mass transport data were obtained by monitoring the (first order) concentration decay of dissolved zinc in sulfate media at pH 2. The electrolyses were performed at holding potential of −1.7 V vs. sat. MSE at Reynolds numbers comprised between 15 470 ≤ Re ≤ 123 680. Based on the analysis of Sh = aRe^bSc^0.356 correlation, the value of the constant a, associated with shape and cell dimensions, was 0.65; while the constant b, associated with hydrodynamic regime, exhibits a value of 0.48, which obeys to smooth zinc deposits on RCE interface. The mass transport in the Zn(II)/Zn cathode interface process differs with other deposition process, which usually gives roughness deposits.     

The prediction of transport parameters in filamentous fermentation broths based on results obtained in pseudoplastic polymer solutions

Transport phenomena studies on single phase “model” fluids are of limited value in biochemical engineering if they cannot be translated to the heterogeneous systems encountered in real fermentation processes. In this paper we discuss the utility of polymer solutions as models of filamentous fermentation broths for evaluation of: pipeline friction factors and impeller power numbers (turbine and helical ribbon). To a first approximation, polymer solutions can serve as suitable models for the prediction of laminar flow pressure drop in pipelines and turbulent power consumption in stirred tanks. However, results obtained on polymer solutions do not directly apply to filamentous fermentation broths for predictions of laminar flow impeller power consumption and the transition point for turbulent flow in stirred tanks. These discrepancies are believed to result from the existence of a time dependent yield stress in filamentous fermentation broths.