The dynamics of polymerized carbon nanotubes in semiconductor polymer electronics and electro-mechanical sensing

Polymerized carbon nanotubes (CNTs) are promising materials for polymer-based electronics and electro-mechanical sensors. The advantage of having a polymer nanolayer on CNTs widens the scope for functionalizing it in various ways for polymer electronic devices. However, in this paper, we show for the first time experimentally that, due to a resistive polymer layer having carbon nanoparticle inclusions and polymerized carbon nanotubes, an interesting dynamics can be exploited. We first show analytically that the relative change in the resistance of a single isolated semiconductive nanotube is directly proportional to the axial and torsional dynamic strains, when the strains are small, whereas, in polymerized CNTs, the viscoelasticity of the polymer and its effective electrical polarization give rise to nonlinear effects as a function of frequency and bias voltage. A simplified formula is derived to account for these effects and validated in the light of experimental results. CNT–polymer-based channels have been fabricated on a PZT substrate. Strain sensing performance of such a one-dimensional channel structure is reported. For a single frequency modulated sine pulse as input, which is common in elastic and acoustic wave-based diagnostics, imaging, microwave devices, energy harvesting, etc, the performance of the fabricated channel has been found to be promising.

Electrochromic, magnetotransport and AC transport properties of vapor phase polymerized PEDOT(VPP PEDOT)

Poly(3,4-ethylenedioxy)thiophene (PEDOT) doped with tosylate ion (PEDOT-tosylate or VPP PEDOT) was synthesized by vapor phase polymerization (VPP) technique on glass as well as on glass/ITO and the electrochromic properties were investigated. Compared with that of PEDOT-PSS spin-coated on glass/ITO, the studies showed that VPP PEDOT has a lower work function and better electrochromic properties. The magneto and AC transport properties studies were done on VPP PEDOT coated on glass substrate. The system shows 2-dimensional variable range hopping and wave function shrinkage of charge carriers.

Supercapacitor studies of electrochemically deposited PEDOT on stainless steel substrate

There has been increasing interest on various properties and applications of electronically conducting polymers. Polyethylenedioxythiophene (PEDOT) is an interesting polymer of this type as it exhibits very high ionic conductivity. In the present study, PEDOT has been electrochemically deposited on stainless steel (SS) substrate for supercapacitor studies. PEDOT/SS electrodes prepared in 0.1M H2SO4 in presence of a surfactant, sodium dodecylsulphate (SDS), have been found to yield higher specific capacitance (SC) than the electrodes prepared from neutral aqueous electrolyte. The effects of concentration of H(2)SO4(,) concentration of SDS, potential of deposition, and nature of supporting electrolytes used for capacitor studies on SC of the PEDOT/SS electrodes have been studied. SC values as high as 250 F/g in 1M oxalic acid have been obtained during the initial stages of cycling. However, there is a rapid decrease in SC on repeated charge-discharge cycling. Spectroscopic data reflect structural changes in PEDOT on extended cycling. (C) 2007 Wiley Periodicals, Inc.

Can one electrochemically measure the statistical morphology of a rough electrode

We have developed a theory for an electrochemical way of measuring the statistical properties of a nonfractally rough electrode. We obtained the expression for the current transient on a rough electrode which shows three times regions: short and long time limits and the transition region between them. The expressions for these time ranges are exploited to extract morphological information about the surface roughness. In the short and long time regimes, we extract information regarding various morphological features like the roughness factor, average roughness, curvature, correlation length, dimensionality of roughness, and polynomial approximation for the correlation function. The formulas for the surface structure factors (the measure of surface roughness) of rough surfaces in terms of measured reversible and diffusion-limited current transients are also obtained. Finally, we explore the feasibility of making such measurements.

An electrochemically impregnated sintered-nickel electrode

An electrochemically impregnated sintered-nickel porous electrode with a capacity of 225 +/- 10 mAh per g of active material has been developed. This capacity is comparable with any state-of-the-art nickel hydroxide electrode reported in the literature, such as the stabilized alpha-nickel hydroxides that contain aluminium, iron and other trivalent cations. A technical update on various types of nickel positive electrodes is given.

Characterization of electrochemically deposited Cu-Ni black coatings

Electrochemically deposited Cu-Ni black coatings on molybdenum substrate from ethylenediaminetetraacetic acid (EDTA) bath solution are shown to exhibit good optical properties (alpha = 0.94, epsilon = 0.09). The deposit is characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Cu is present in metallic and +2 oxidation states in the as-prepared Cu-Ni black coating, whereas Ni2+ as well as Ni3+ species are observed in the same coating. Cu and Ni are observed in their metallic state after 10 and 20 min sputtering. X-ray initiated Auger electron spectroscopy (XAES) of Cu and Ni also agrees well with XPS investigations. (C) 2002 Elsevier Science Ltd. All rights reserved.

Electrochemically deposited crystalline thin film of polyaniline on nickel for redox reactions at positive potentials

Redox reactions which occur at positive potentials such as ferrous/ferric, hydroquinone/quinone, ferrocyanide/ferricyanide etc. in aqueous acidic electrolytes cannot be studied on non-platinum metals, for example, a Ni electrode. On the contrary, these reactions occur on polyaniline (PANI) modified Ni electrodes, as evidenced from cyclic voltammetry, amperometry and steady-state polarization experiments. Under identical experimental conditions of scan rate (v) and concentration (C), the peak current density (i(p)) values of Fe2+/Fe3+ redox reaction are greater on the PANI modified Ni than on Pt. Additionally, the peak potential separation (DeltaE(p)) of the voltammogram is lesser on the PANI modified Ni. With an increase in thickness of the PANI, DeltaE(p) increases suggesting that the redox reactions tend to depart from the reversibility. Scanning electron micrographs reveal the presence of a crystalline deposit of PANI on Ni when the thickness of PANI is about 0.08 mum. However, the PANI becomes amorphous and porous at higher thickness values. Raman spectroscopy and X-ray diffraction studies corroborate the observations made out of scanning electron microscopy. Higher catalytic activity of PANI is attributed to crystalline nature of PANI on Ni. Exchange current density and standard rate constant of Fe2+/Fe(3+)redox reaction are evaluated. (C) 2002 Published by Elsevier Science B.V.

Field dependent and disorder-induced nonlinear charge transport in electrochemically doped polypyrrole devices

Electric field activated charge transport is studied in the metal/polymer/metal device structure of electropolymerized polypyrrole down to 10 K with varying carrier density and disorder. Disorder induced nonlinear behaviour is observed in polypyrrole devices grown at room temperature which is correlated to delocalization of states. The slope parameter of currentvoltage characteristics (in log-log scale) increases as the temperature decreases, which indicates the onset of stronger field dependence. The field dependence of mobility becomes dominant as the carrier density decreases. The sharp dip in differential conductance indicates the localization of carriers at low temperatures which reduces the effective number of carriers involved in the transport.

Simultaneous Determination of Catecholamines in Presence of Uric Acid and Ascorbic Acid at a Highly Sensitive Electrochemically Activated Carbon Paste Electrode

A simple yet remarkable, electrochemically activated carbon paste electrode (EACPE) was prepared by successive potential cycling of carbon paste in a 0.1 M NaOH solution and was effectively used for the simultaneous determination of catecholamines such as dopamine (DA), epinephrine (E) and Norepinephrine (NE) in presence of uric acid (UA) and ascorbic acid (AA). Taking DA as the ideal catecholamine, the electrochemical behaviors of DA, UA and AA such as scan rate and pH variation was studied by cyclic voltammetry (CV) in phosphate buffer solution (PBS, pH 7.1). This electrochemical sensor exhibited strong electrocatalytic activity towards the oxidation of a mixture of catecholamines, UA and AA with apparent reduction of overpotentials. Crider optimum conditions, limit of detection (S/N = 3) of DA, E, NE, UA and AA was found to be 0.08, 0.08, 0.07, 0.1 and 6.0 mu M, respectively by differential pulse voltammetry (DPV). The analytical performance of this modified electrode as a biosensor was also demonstrated for the determination of DA, UA and AA in dopamine injection, human urine and vitamin C tablets, respectively, in presence of other interfering substances. (C) 2015 The Electrochemical Society. All-rights reserved.

Fluctuations in protein synthesis from a single RNA template: Stochastic kinetics of ribosomes

Proteins are polymerized by cyclic machines called ribosomes, which use their messenger RNA (mRNA) track also as the corresponding template, and the process is called translation. We explore, in depth and detail, the stochastic nature of the translation. We compute various distributions associated with the translation process; one of them-namely, the dwell time distribution-has been measured in recent single-ribosome experiments. The form of the distribution, which fits best with our simulation data, is consistent with that extracted from the experimental data. For our computations, we use a model that captures both the mechanochemistry of each individual ribosome and their steric interactions. We also demonstrate the effects of the sequence inhomogeneities of real genes on the fluctuations and noise in translation. Finally, inspired by recent advances in the experimental techniques of manipulating single ribosomes, we make theoretical predictions on the force-velocity relation for individual ribosomes. In principle, all our predictions can be tested by carrying out in vitro experiments.

First donor-acceptor interaction promoted gelation of organic fluids

In recent years there has been considerable interest in developing new types of gelators of organic solvents.1 Despite the recent advances, a priori design of a gelator for gelling a given solvent has remained a challenging task. Various noncovalent interactions like hydrogen-bonding,2 metal coordination3 etc. have been used as the driving force for the gelation process. A special class of cholesterol-based gelators were reported by Weiss,4 and by Shinkai.5 Gels derived from these molecules have been used for chiral recognition/sensing,6 for studying photo- and metal-responsive functions,7 and as templates to make hollow fiber silica.8 Other types of organogels have been used for designing polymerized 9 and reverse aerogels,10 and in molecular imprinting.11 Hanabusa’s group has recently reported organogels with a bile acid derivative.12 This has prompted us to disclose our results on a novel electron donor–acceptor (EDA) interaction mediated two-component13 gelator system based on the bile acid14 backbone.

Pt metal-CeO2 interaction: Direct observation of redox coupling between Pt-0/Pt2+/Pt4+ and Ce4+/Ce3+ states in Ce0.98Pt0.02O2-delta catalyst by a combined electrochemical and x-ray photoelectron spectroscopy study

Pt ions-CeO2 interaction in Ce1-xPtxO2-delta (x=0.02) has been studied for the first time by electrochemical method combined with x-ray diffraction and x-ray photoelectron spectroscopy. Working electrodes made of CeO2 and Ce0.98Pt0.02O2-delta mixed with 30% carbon are treated electrochemically between 0.0-1.2 V in potentiostatic (chronoamperometry) and potentiodynamic (cyclic voltametry) mode with reference to saturated calomel electrode. Reversible oxidation of Pt-0 to Pt2+ and Pt4+ state due to the applied positive potential is coupled to simultaneous reversible reduction of Ce4+ to Ce3+ state. CeO2 reduces to CeO2-y (y=0.35) after applying 1.2 V, which is not reversible; Ce0.98Pt0.02O2-delta reaches a steady state with Pt2+:Pt4+ in the ratio of 0.60:0.40 and Ce4+:Ce3+ in the ratio of 0.55:0.45 giving a composition Ce0.98Pt0.02O1.74 at 1.2 V, which is reversible. Composition of Pt ion substituted compound is reversible between Ce0.98Pt0.02O1.95 to Ce0.98Pt0.02O1.74 within the potential range of 0.0-1.2 V. Thus, Ce0.98Pt0.02O2-delta forms a stable electrode for oxidation of H2O to O-2 unlike CeO2. A linear relation between oxidation of Pt2+ to Pt4+ with simultaneous reduction in Ce4+ to Ce3+ is observed demonstrating Pt-CeO2 metal support interaction is due to reversible Pt-0/Pt2+/Pt4+ interaction with Ce4+/Ce3+ redox couple.

Simultaneous Electrodeposition of MnO2 and Mn(OH)(2) for Supercapacitor Studies

Among the various Mn compounds, both MnO2 and Mn(OH)2 are electrochemically active in supercapacitor studies. MnO2 and Mn(OH)2 are simultaneously deposited, through a one-pot method, on the anode and cathode, respectively, of a galvanostatic electrolysis cell consisting of aqueous Mn(NO3)2 electrolyte. MnO2 and Mn(OH)2 coated stainless steel (SS) electrodes are found to exhibit a capacitive behavior with a high specific capacitance. MnO2/SS and Mn(OH)2/SS electrodes are used as the negative and positive electrodes, respectively, in assembling nonsymmetrical capacitors and testing. The results indicate that both Mn-based electrodes prepared simultaneously in a single electrolysis possess interesting electrochemical properties for supercapacitor application.

Electrochemical Reduction of Oriented Graphene Oxide Films: An in Situ Raman Spectroelectrochemical Study

Graphene oxide (GO) is assembled on a gold substrate by a layer-by-layer technique using a self-assembled cystamine monolayer. The negatively charged GO platelets are attached to the positively charged cystamine monolayer through electrostatic interactions. Subsequently, it is shown that the GO can be reduced electrochemically using applied DC bias by scanning the potential from 0 to -1 V vs a saturated calomel electrode in an aqueous electrolyte. The GO and reduced graphene oxide (RGO) are characterized by Raman spectroscopy and atomic force microscopy (AFM). A clear shift of the G band from 1610 cm-1 of GO to 1585 cm-1 of RGO is observed. The electrochemical reduction is followed in situ by micro Raman spectroscopy by carrying out Raman spectroscopic studies during the application of DC bias. The GO and RGO films have been characterized by conductive AFM that shows an increase in the current flow by at least 3 orders of magnitude after reduction. The electrochemical method of reducing GO may open up another way of controlling the reduction of GO and the extent of reduction to obtain highly conducting graphene on electrode materials.