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Influence of normal and radial contributions of local current density on local electrochemical impedance spectroscopy

Ferrari, Jean Vicente; Melo, Hercilio Gomes de; Keddam, M.; Orazem, M. E.; Pébère, Nadine; Tribollet, Bernard; Vivier, V.
Fonte: Pergamon-Elsevier Science Ltd; Oxford Publicador: Pergamon-Elsevier Science Ltd; Oxford
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
36.44%
A new tri-electrode probe is presented and applied to local electrochemical impedance spectroscopy (LEIS) measurements. As opposed to two-probe systems, the three-probe one allows measurement not only of normal, but also of radial contributions of local current densities to the local impedance values. The results concerning the cases of the blocking electrode and the electrode with faradaic reaction are discussed from the theoretical point of view for a disk electrode. Numerical simulations and experimental results are compared for the case of the ferri/ferrocyanide electrode reaction at the Pt working electrode disk. At the centre of the disk, the impedance taking into account both normal and radial contributions was in good agreement with the local impedance measured in terms of only the normal contribution. At the periphery of the electrode, the impedance taking into account both normal and radial contributions differed significantly from the local impedance measured in terms of only the normal contribution. The radial impedance results at the periphery of the electrode are in good agreement with the usual explanation that the associated larger current density is attributed to the geometry of the electrode, which exhibits a greater accessibility at the electrode edge. (C) 2011 Elsevier Ltd. All rights reserved.; CAPES; Charles A. Stokes professorship

Estudo da corrosão localizada da liga de alumínio 7475-T761 por espectroscopia de impedância eletroquímica global e local em meio de sulfato de sódio.; Localized corrosion study of aluminum alloy 7475-T761 in sulfate medium using global and local electrochemical impedance spectroscopy.

Ferrari, Jean Vicente
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 20/07/2011 PT
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As ligas de Al utilizadas na indústria aeroespacial com finalidade estrutural apresentam microestrutura complexa devido aos tratamentos termo-mecânicos a que são submetidas visando o aumento da resistência mecânica. Estas ligas se caracterizam pela presença de um grande número de intermetálicos (IMs) em sua microestrutura, os quais possuem atividade eletroquímica diferente da matriz provocando problemas de corrosão localizada devido à formação de microcélulas galvânicas. Na última década a espectroscopia de impedância eletroquímica (LEIS) tem se estabelecido como uma poderosa técnica na elucidação de aspectos locais relacionados à corrosão, e também tem servido para estudos de aspectos teóricos referentes à distribuição de potencial e corrente na superfície de eletrodos e suas correlações com a reatividade superficial. Esta técnica se baseia na análise de diferentes impedâncias locais obtidas por meio de um bi-eletrodo posicionado nas proximidades do eletrodo de trabalho. O presente trabalho visa estudar a corrosão localizada da liga de Al 7475-T761, utilizada na estrutura de asas e na fuselagem de aeronaves, em meios contendo íons sulfato por meio de espectroscopia de impedância eletroquímica global (EIS) e por LEIS...

Estudo da eletro-oxidação do etanol utilizando eletrocatalisadores PtPd/C+ATO e PtPdSn/C+ATO preparados via redução por borohidreto de sódio; Study on ethanol electro-oxidation using PtPd/C+ATO and PtPdSn/C+ATO catalysts prepared by the reduction by sodium borohydride method

Piasentin, Ricardo Marcelo
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 25/06/2013 PT
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16.25%
Em uma primeira etapa, os catalisadores eletroquímicos de Pt/C, Pt/C+ATO, Pd/C, Pd/C+ATO, PtPd/C+ATO e PtPdSn/C+ATO, onde foram usadas diferentes razões molares de Pt e Pd, e de Pt, Pd e Sn, respectivamente, foram preparados pelo método de redução por borohidreto de sódio para serem testados na oxidação do etanol. H2PtCl6.6H2O, Pd(NO3)2.2H2O e SnCl2.2H2O foram utilizados como fontes de metais, que corresponderam a 20% em massa do catalisador. A mistura física de 85% de carbono Vulcan XC72 e 15% de Sb2O5.SnO2 (ATO) foi utilizada como suporte. Os catalisadores foram caracterizados por meio da difração de raios X, microscopia de transmissão, voltametria cíclica, cronoamperometria, teste em célula unitária de etanol direto e espectroscopia de infravermelho com transformada de Fourier in situ (ATR-FTIR). Os difratogramas de raios X de Pt/C e Pd/C mostraram quatro picos associados com a estrutura cúbica de face centrada (cfc) da platina e do paládio, respectivamente. Já para os catalisadores de Pt, Pd, PtPd e PtPdSn, suportados em carbono e ATO puderam ser visualizados, além dos picos referentes à Pt e ao Pd, outros oito picos associados com a cassiterita e/ou com os óxidos de estanho dopado com antimônio (ATO). A microscopia de transmissão mostrou que todos os catalisadores apresentam suas partículas metálicas homogeneamente distribuídas no suporte e seus tamanhos variaram de 2 a 6 nm. Os estudos eletroquímicos de voltametria e cronoamperometria em meio de H2SO4 indicaram que os catalisadores terciários de PtPdSn(80:10:10)/C+ATO e PtPdSn(90:5:5)/C+ATO...

Electrochemical Oxidation of Ketenedithioacetals

Curi,Denise; Pardini,Vera L.; Viertler,Hans
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/02/1998 EN
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15.97%
Anodic oxidation of ketenedithioacetals 1, R¹R²C=C(SMe)2, is reported in this work. Cyclic voltammetry performed in dry MeCN 0.1 M NaClO4 using Pt bead as anode and Ag/AgI as reference electrode showed an irreversible oxidation step. The corresponding oxidation peak potentials were slightly dependent on the carbon-carbon double bond substitution pattern (tri- vs. tetrasubstitution) but showed a strong dependence upon the nature of the R groups. The main products of the controlled potential preparative electrolyses in 0.2 M NaClO4 aqueous acetonitrile were dimers for R¹ =n-Pr or C6H5C(O) and R² =H, and alpha-hydroxy-thioesters and monosulfoxides for the substrates with tetrasubstituted carbon-carbon double bonds.

Equilibrium Potentials of Membrane Electrodes

Wang, Jui H.; Copeland, Eva
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /07/1973 EN
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A simple thermodynamic theory of the equilibrium potentials of membrane electrodes is formulated and applied to the glass electrode for measurement of pH. The new formulation assumes the selective adsorption or binding of specific ions on the surface of the membrane which may or may not be permeable to the ion, and includes the conventional derivation based on reversible ion transport across membranes as a special case. To test the theory, a platinum wire was coated with a mixture of stearic acid and methyl-tri-n-octyl-ammonium stearate. When this coated electrode was immersed in aqueous phosphate solution, its potential was found to be a linear function of pH from pH 2 to 12 with a slope equal to the theoretical value of 59.0 mV per pH unit at 24°.

Electrical activation of common bile duct nerves modulates sphincter of Oddi motility in the Australian possum

Sonoda, Y.; Takahata, S.; Jabar, F.; Schloithe, A. C.; Grivell, M. A.; Woods, C. M.; Simula, M. E.; Toouli, J.; Saccone, G. T. P.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em //2005 EN
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15.97%
Background: Sphincter of Oddi (SO) motility is regulated by extrinsic and intrinsic nerves. The existence of neural circuits between the SO and the proximal extrahepatic biliary tree has been reported, but they are poorly understood. Using electrical field stimulation (EFS), we determined if a neural circuit exists between the common bile duct (CBD) and the SO in anaesthetized Australian brush-tailed possums. Methods: The gallbladder, cystic duct or CBD were subjected to EFS with a stimulating electrode. Spontaneous SO phasic waves were measured by manometry. Results: EFS at sites on the distal CBD (12–20 mm proximal to the SO), but less commonly at more proximal CBD, evoked a variety of responses consisting of an excitatory and/or inhibitory phase. Bi-phasic responses consisting of an excitation followed by inhibition were the most common. Tri-phasic responses were also observed as well as excitation or inhibition only. These evoked responses were blocked by topical application of local anaesthetic to the distal CBD or transection of the CBD. EFS at sites on the gallbladder body, neck or cystic duct did not consistently evoke an SO response. Pretreatment with atropine or guanethidine reduced the magnitude of the evoked response by about 50% (p<0.05)...

Effects of Stimulation Mode, Level and Location on Forward-Masked Excitation Patterns in Cochlear Implant Patients

Chatterjee, Monita; Galvin, John J.; Fu, Qian-Jie; Shannon, Robert V.
Fonte: Springer-Verlag Publicador: Springer-Verlag
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
16.14%
In multi-channel cochlear implants, electrical current is delivered to appropriate electrodes in the cochlea to approximate the spatial representation of speech. Theoretically, electrode configurations that restrict the current spread within the cochlea (e.g., bi- or tri-polar stimulation) may provide better spatial selectivity, and in turn, better speech recognition than configurations that produce a broader current spread (e.g., monopolar stimulation). However, the effects of electrode configuration on supra-threshold excitation patterns have not been systematically studied in cochlear implant patients. In the present study, forward-masked excitation patterns were measured in cochlear implant patients as functions of stimulation mode, level and location within the cochlea. All stimuli were 500 pulses-per-second biphasic pulse trains (200 μs/phase, 20 μs inter-phase gap). Masker stimuli were 200 ms in duration; the bi-polar configuration was varied from narrow (BP + 1) to wide (BP + 17), depending on the test condition. Probe stimuli were 20 ms in duration and the masker-probe delay was 5 ms; the probe configuration was fixed at BP + 1. The results indicated that as the distance between the active and return electrodes in a bi-polar pair was increased...

Voltage Dependence of Proton Pumping by Bacteriorhodopsin Mutants with Altered Lifetime of the M Intermediate

Geibel, Sven; Lörinczi, Èva; Bamberg, Ernst; Friedrich, Thomas
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Publicado em 03/09/2013 EN
Relevância na Pesquisa
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The light-driven proton pump bacteriorhodopsin (BR) from Halobacterium salinarum is tightly regulated by the [H+] gradient and transmembrane potential. BR exhibits optoelectric properties, since spectral changes during the photocycle are kinetically controlled by voltage, which predestines BR for optical storage or processing devices. BR mutants with prolonged lifetime of the blue-shifted M intermediate would be advantageous, but the optoelectric properties of such mutants are still elusive. Using expression in Xenopus oocytes and two-electrode voltage-clamping, we analyzed photocurrents of BR mutants with kinetically destabilized (F171C, F219L) or stabilized (D96N, D96G) M intermediate in response to green light (to probe H+ pumping) and blue laser flashes (to probe accumulation/decay of M). These mutants have divergent M lifetimes. As for BR-WT, this strictly correlates with the voltage dependence of H+ pumping. BR-F171C and BR-F219L showed photocurrents similar to BR-WT. Yet, BR-F171C showed a weaker voltage dependence of proton pumping. For both mutants, blue laser flashes applied during and after green-light illumination showed reduced M accumulation and shorter M lifetime. In contrast, BR-D96G and BR-D96N exhibited small photocurrents...

High-density distributed electrode network, a multi-functional electroporation method for delivery of molecules of different sizes

Wu, Mengxi; Zhao, Deyao; Zhong, Wenfeng; Yan, Hao; Wang, Xiaoxia; Liang, Zicai; Li, Zhihong
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Artigo de Revista Científica
Publicado em 28/11/2013 EN
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We present a multi-functional electroporation method for delivery of biomolecule utilizing a high-density distributed electrode network (HDEN) under tri-phase electric stimulation. The HDEN device, with which drastic pH change during the electroporation was avoided,was demonstrated to be highly effective for transfection of not only DNA plasmids and small interfering RNAs (siRNA), but also a small molecular anti-cancer drug, into cells in adjustable volumes of cell suspension. The method constitutes a very flexible electroporation approach in a wide range of in vitro or ex vivo scenarios in various tubes, standard multi-well plates as well as flow chambers.

Strontium (II)-Selective Potentiometric Sensor Based on Ester Derivative of 4-tert-butylcalix(8)arene in PVC Matrix

Jain, Ajay K.; Gupta, Vinod K.; Raisoni, Jitendra R.
Fonte: Molecular Diversity Preservation International (MDPI) Publicador: Molecular Diversity Preservation International (MDPI)
Tipo: Artigo de Revista Científica
Publicado em 30/08/2004 EN
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Membranes of 4-tert-butylcalix(8)arene-octaacetic acid octaethyl ester (I) as an electroactive material, sodium tetraphenyl borate (NaTPB) as an anion excluder, and tri-n-butyl phosphate (TBP) as a solvent mediator in poly(vinyl chloride) (PVC) matrix have been tried for a strontium-selective sensor. The best performance was exhibited by the membrane having a composition 5:100:150:2 (I: PVC: TBP: NaTPB (w/w)). This sensor exhibits a good potentiometric response to Sr2+ over a wide concentration range (3.2 × 10 –5 –1.0 × 10 –1 M) with a Nernstian slope (30 mV/ decade). The response time of the sensor is 10 s and it has been used for a period of four months without any drift in potentials. The selectivity coefficient values are in the order of 0.01 for mono-, bi-, and trivalent cations which indicate a good selectivity for Sr2+ over a large number of cations. The useful pH range for the sensor was found to be 3-10 and it works well in mixtures with non-aqueous content up to 25 % (v/v). The sensor has been used as an indicator electrode in the potentiometric titration of Sr2+ against EDTA.

Poly[3,4-ethylene dioxythiophene (EDOT) –co– 1,3,5-tri[2-(3,4-ethylene dioxythienyl)]-benzene (EPh)] copolymers (PEDOT-co-EPh): optical, electrochemical and mechanical properties

Ouyang, Liangqi; Kuo, Chin-chen; Farrell, Brendan; Pathak, Sheevangi; Wei, Bin; Qu, Jing; Martin, David C.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
25.97%
PEDOT-co-EPh copolymers with systematic variations in composition were prepared by electrochemical polymerization from mixed monomer solutions in acetonitrile. The EPh monomer is a trifunctional crosslinking agent with three EDOTs around a central benzene ring. With increasing EPh content, the color of the copolymers changed from blue to yellow to red due to decreased absorption in the near infrared (IR) spectrum and increased absorption in the visible spectrum. The surface morphology changed from rough and nanofibrillar to more smooth with rounded bumps. The electrical transport properties dramatically decreased with increasing EPh content, resulting in coatings that either substantially lowered the impedance of the electrode (at the lowest EPh content), leave the impedance nearly unchanged (near 1% EPh), or significantly increase the impedance (at 1% and above). The mechanical properties of the films were substantially improved with EPh content, with the 0.5% EPh films showing an estimated 5x improvement in modulus measured by AFM nanoindentation. The PEDOT-co-EPh copolymer films were all shown to be non-cytotoxic toward and promote the neurite outgrowth of PC12 cells. Given these results, we expect that the films of most interest for neural interface applications will be those with improved mechanical properties that maintain the improved charge transport performance (with 1% EPh and below).

A New Bias Method of an Electron Gun

MUNAKATA, Chusuke; WATANABE, Hiroshi
Fonte: Oxford University Press Publicador: Oxford University Press
Tipo: Artigo de Revista Científica Formato: text/html
EN
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It is well known that the “self-bias” system in an ordinary tri-electrode electron gun forms a negative feed back loop for the beam current of the gun, and stabilizes the current. The better stability of beam current against high voltage fluctuation can be attained by using the higher resistor in the bias circuit. The total beam current, however, decreases with the higher resistor. In another word, it is difficult to obtain the high stability and high intensity of the beam current at the same time. A new bias system which may be called “half-fixed bias” overcomes the difficulty mentioned above. Analyses of the bias system are performed by making use of the triode equation which is commonly used in the field of electronic engineering. Fairly good agreement between calculated values and experimental results is found.

Study of plasma-surface kinetics and feature profile simulation of poly-silicon etching in Cl²/HBr plasma

Jin, Weidong, 1975-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 185 p.; 6956603 bytes; 6956392 bytes; application/pdf; application/pdf
EN_US
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This work characterized the Cl2/HBr ion enhanced plasma-surface interactions with poly-silicon as a function of the gas composition, ion energy, ion incident angle and other important process parameters. A realistic inductively coupled plasma beam apparatus capable of generating ions and neutrals representative of real commercial etcher was constructed and utilized to simulate accurately a high density plasma environment. Etching rate of poly- silicon, the oxygen effect and loading effect are quantified to better describe the etching of patterned poly-silicon in fabricating the gate electrode of a transistor in VLSI manufacturing process. The kinetics model derived from these measurements are incorporated into a Monte Carlo based feature profile simulator, and profile evolution has been simulated under various processing conditions. The realistic plasma beam was used to measure the etching yields of poly-silicon with Cl2/HBr chemistry at different ion energies. The etching yields were found to scale linearly with ... where the threshold energies, Eth are 10 eV for both Cl2 and HBr. The etching yields at different neutral-to-ion flux ratio were measured and the sticking coefficients are derived for reactive neutrals for Cl2 and HBr. The sticking coefficient for HBr system is lower probably due to the relatively larger size of bromine atom compared with chlorine and its relatively lower chemical reactivity. The etching yields for mixed Cl2+HBr plasma at different compositions were also measured.; (cont.) The etching yield by the HBr plasma beam is similar to the C12 plasma beam...

Surface Enhanced Electrochemiluminescence of Ru(bpy)32+

Wang, Daifang; Guo, Longhua; Huang, Rong; Qiu, Bin; Lin, Zhenyu; Chen, Guonan
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Artigo de Revista Científica
Publicado em 22/01/2015 EN
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Surface enhanced spectroscopy such as surface enhanced Raman spectrum (SERS) and surface enhanced fluorescence have been investigated extensively in the past two decades. Herein, we present experimental evidence to demonstrate the existence of a new surface enhanced spectroscopy, namely, surface enhanced electrochemiluminescence (SEECL). Our investigation indicates that the electrochemiluminescence (ECL) response of the Ru(bpy)32+-tri-n-propylamine (TPrA) system could be significantly enhanced when the working electrode is modified with gold nanoparticle-SiO2 core-shell nanocomposites (AuNP@SiO2). It is worth noting that comparing with a working electrode modified with pure SiO2 nanoparticles, the electrochemical responses of the two electrodes were quite similar, but the ECL signal of the AuNP@SiO2 modified electrode was ~5 times higher than that of the SiO2 nanoparticles modified electrode. Thus we infer that the localized surface plasmon resonance (LSPR) of the AuNPs could be a major contribution to the ECL enhancement. Our investigations also demonstrate that the ECL enhancement is closely related to the thickness of the SiO2 layer. As much as 10 times ECL enhancement (comparing with the ECL intensity of bare electrode) is observed under the optimal conditions. The possible mechanism of the SEECL phenomenon is also discussed.

Effect of plasticizer type on the potentiometric selectivity coefficient of electrodes for nitarte ion determination constructed by using PVC as polymeric membrane.

Yazdani-Pedram Zobeiri, Mehrdad; Cortés Nodarse, I.; Pérez Saavedra, J. J.; Arada Pérez, María de los Angeles
Fonte: Ministerio de Educación Superior Publicador: Ministerio de Educación Superior
Tipo: Artículo de revista
ES
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Seven types of chemical sensors based on polymeric liquid membranes for determination of nitrate ion have been prepared by using 3-nitro-o-xylene (NOX), tri-butyphosphate (TBP), bis-(2-ethylhexyl)sebacate (DOS), o-nitrophenyloctyl ether (o-NPOE), tris-2ethylhexylphosphate (TEHP), dioctylphthalate (DOP) and dibutylphthalate (DBP) as plasticizers, tri-octyl methyl ammonium chloride (TOMACI) as ionophoreas ionophore and poly (vinyl chloride) (PVC) as matrix. The experimental data was validated by calibrating each constructed sensor against a reference AG/AgCl electrode. The calibration parameters for each sensor was determined by applying the method of the addition solutions and the potentiometric selectivity coefficient (K Pot AB) of each electrode was determined by applying the method of mixed solutions. The response of the sensors was determined in relation with the lipophilicity od each plasticizer used solvent-mediator, its dielectric constant (er), polarity and viscosity. No correlation between the calculated calues for K Pot AB of the electrodes and dielectric constant of the plasticizers was observed.

Audio mixing in a tri-port nano-electro-mechanical device

Defoort, M.; Lulla, K.; Heron, J. -S.; Bourgeois, O.; Collin, E.; Pistolesi, Fabio
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 06/09/2011
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We report on experiments performed on a cantilever-based tri-port nano-electro-mechanical (NEMS) device. Two ports are used for actuation and detection through the magnetomotive scheme, while the third port is a capacitively coupled gate electrode. By applying a low frequency voltage signal on the gate, we demonstrate mixing in the mechanical response of the device, even for {\it low magnetomotive drives, without resorting to conduction measurements through the NEMS}. The technique can thus be used in particular in the linear regime, as an alternative to nonlinear mixing, for normal conducting devices. An analytic theory is presented reproducing the data without free parameters

Iridium oxide-carbon hybrid materials as electrodes for neural systems. Electrochemical synthesis and characterization

Carretero González, Nina Magali; Casabó i Gispert, Jaume
Fonte: [Barcelona] : Universitat Autònoma de Barcelona, Publicador: [Barcelona] : Universitat Autònoma de Barcelona,
Tipo: Tesis i dissertacions electròniques; info:eu-repo/semantics/doctoralThesis; info:eu-repo/semantics/publishedVersion Formato: application/pdf
Publicado em //2014 ENG
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El desarrollo de interfaces neuronales requiere el uso de nuevos materiales electroactivos y biocompatibles, que al aplicar campos eléctricos no causen efectos secundarios que pueden dañar los tejidos o degradar la funcionalidad del electrodo. A día de hoy, existen diferentes materiales electroactivos que se usan como electrodos en el sistema nervioso: oro, platino, carbón, Pt-Ir o IrOx entre otros, siendo este último el que ha mostrado superiores resultados. Una alta eficiencia electroquímica, estabilidad en condiciones biológicas y biocompatibilidad, han hecho del IrOx el material más prometedor como electrodo para estimulación y registro de señales neuronales. Sin embargo, los avances tecnológicos han generado una demanda de nuevos materiales con propiedades mejoradas y con menos inconvenientes que los actuales (bajos valores de capacidad de carga o la rigidez inherente de este tipo de óxidos, ya que presentan poca compatibilidad con los tejidos blandos). Estas mejoras se pueden conseguir con el uso de materiales híbridos, que unan las diferentes propiedades de los componentes. En este sentido, se han preparado electroquímicamente híbridos IrOx-CNTs, con propiedades mejoradas tras la adicción de nanotubos de carbono. La composición química de estos híbridos es muy parecida a la obtenida para IrOx...

Desarrollo y caracterización de sensores químicos de estado sólido para aplicaciones biomédicas

Zine, Nadia
Fonte: Bellaterra : Universitat Autònoma de Barcelona, Publicador: Bellaterra : Universitat Autònoma de Barcelona,
Tipo: Tesis i dissertacions electròniques; info:eu-repo/semantics/doctoralThesis Formato: application/pdf
Publicado em //2005 SPA; SPA
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16.48%
Consultable des del TDX; Títol obtingut de la portada digitalitzada; El trabajo realizado para la tesis se ha centrado en el desarrollo y el estudio de multi-sensores químicos basados en silicio para aplicaciones biomédicas. Dicho trabajo se divide en tres partes: En la primera parte se han fabricado sensores de silicio basados en transistores de efecto de campo sensibles a iones (ISFET). El dispositivo tiene forma de aguja e incluye dos sensores ISFETs, un pseudo-electrodo de referencia de platino y un sensor de temperatura basado en una resistencia de platino. Los ISFETs se han caracterizado eléctricamente como transistores MOSFET y químicamente como sensores de pH, con resultados satisfactorios, lo que ha demostrado la viabilidad de las tecnologías de fabricación. Se han desarrollado MEMFETs selectivos al ión potasio depositando sobre el ISFET una membrana polimérica de PVC que contiene la valinomicina como ionóforo. Los sensores mostraron una respuesta de 50 mV/década aproximadamente, en un rango de actividad del ión K+ que va desde 10-4 M hasta 10-1 M. Debido a su gran volumen, el electrodo de referencia estándar no es práctico para trabajar con ISFETs. Por ello se ha estudiado la realización de medidas diferenciales utilizando además del MEMFET de potasio...

Poly[3,4-ethylene dioxythiophene (EDOT)-co-1,3,5-tri[2-(3,4-ethylene dioxythienyl)]-benzene (EPh)] copolymers (PEDOT-co-EPh): optical, electrochemical and mechanical properties

Ouyang, Liangqi; Kuo, Chin-chen; Farrell, Brendan; Pathak, Sheevangi; Wei, Bin; Qu, Jing; Martin, David C.
Fonte: Royal Society of Chemistry. Publicador: Royal Society of Chemistry.
Tipo: Artigo de Revista Científica
EN_US
Relevância na Pesquisa
25.97%
Publisher's PDF; PEDOT-co-EPh copolymers with systematic variations in composition were prepared by electrochemical polymerization from mixed monomer solutions in acetonitrile. The EPh monomer is a trifunctional crosslinking agent with three EDOTs around a central benzene ring. With increasing EPh content, the color of the copolymers changed from blue to yellow to red due to decreased absorption in the near infrared (IR) spectrum and increased absorption in the visible spectrum. The surface morphology changed from rough and nanofibrillar to more smooth with rounded bumps. The electrical transport properties dramatically decreased with increasing EPh content, resulting in coatings that either substantially lowered the impedance of the electrode (at the lowest EPh content), leave the impedance nearly unchanged (near 1% EPh), or significantly increase the impedance (at 1% and above). The mechanical properties of the films were substantially improved with EPh content, with the 0.5% EPh films showing an estimated 5× improvement in modulus measured by AFM nanoindentation. The PEDOT-co-EPh copolymer films were all shown to be non-cytotoxic toward and promote the neurite outgrowth of PC12 cells. Given these results, we expect that the films of most interest for neural interface applications will be those with improved mechanical properties that maintain the improved charge transport performance (with 1% EPh and below).; University of Delaware. Department of Materials Science and Engineering.; University of Delaware. Department of Biomedical Engineering.

In situ electrochemical-ATR-FTIR spectroscopic studies on solution phase 2,4,6-tri-substituted phenoxyl radicals

Webster, Richard
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
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2,4,6-Tri-tert-butylphenolate and 2,6-di-tert-butyl-4- methoxyphenolate (prepared by reacting the corresponding phenols with dry Et4NOH) were oxidised by one-electron in CH3CN at room temperature (with 0.2 M Bu4NPF6 as the supporting electrolyte) in a controlled potential electrolysis cell at negative potentials (-0.68 to -0.84 V vs. Fc/Fc+ (Fc = ferrocene)) to produce moderately stable phenoxyl radicals. The oxidation reaction was monitored using in situ FTIR spectroscopy between 1800-1000 cm-1 with an attenuated total reflectance (ATR) probe containing a diamond composite sensor inserted into the working electrode compartment of the electrolysis cell. Analysis of the data obtained during the chemically reversible oxidation of the phenolate anions allowed the identification of several IR absorption bands that could be assigned to the phenoxyl radicals with notable bands observed at 1592-1573 cm-1 and 1505-1509 cm-1 that were assigned to the ν8a(CoCm ring stretch) and ν7a(Ca-O. stretch) modes, respectively.