486 research outputs found
EC-AFM investigation of reversible volume changes with electrode potential in polyaniline
No full textThe volume changes in electrochemically deposited polyaniline (PANI) on highly oriented pyrolytic graphite (HOPG) in SO42− and Cl− medium along with PANI microtubules and nanowires in SO42− medium were investigated by electrochemical atomic force microscopy (EC-AFM). Volume expansion was observed in the oxidized state with contraction in the reduced state due to the movement of solvated anions inside the polymer matrix during the oxidation process and its expulsion during the reduction process. Reversible volume changes with changing electrochemical potential were observed in case of microtubules and nanowires. To observe the effect of large counter anion, EC-AFM studies of volume changes with electrode potential in polyaniline modified with poly(styrene sulfonate) (PANI–PSS) nanowires were performed in SO42− medium. The changes were found to be more than 33% and in the reverse direction in this case due to presence of larger immobile PSS anion in the polymer matrix with volume changes predominantly due to movement of solvated H+ ions inside the polymer matrix during the reduction process. To further support our observations we performed the in situ electrochemical synthesis of PANI nanoparticles on HOPG inside AFM electrochemical cell and monitored its volume changes with electrode potential using EC-AFM. The volume changes in these nanoparticles could be clearly observed with variation in percentage changes between 17.5% and 89.8%.© Elsevie
Estimation of Equilibrium Capacitance of Polyaniline Films Using Step Voltammetry
No full textThe equilibrium charge storage characteristic of polyaniline films has been determined using step voltammetry technique. The step coulogram (plot of charge stored versus potential) consists of five distinct regions, which correspond to the different energy bands exhibited by the film, in keeping with Raman and ESR spectroscopy data. The coulogram is piecewise linear, with constant capacitance in each band. Effect of the type and concentration of the acid on the equilibrium capacitances of the bands has been studied. The polaron band has the highest capacitance, followed by the bipolaron band and then the polaron lattice band. The charge stored at a given potential is found to be proportional to film mass. The film needs to be polarized to a threshold charge before faradaic charging begins. This faradaic threshold is independent of the type and concentration of the acids. The step coulogram is compared with the sweep coulogram obtained from linear sweep voltammetry. At low sweep rates, the sweep coulogram also exhibits five distinct bands. However, with increase in the sweep rate, the bands progressively reduce in number. The capacitance of the polaron band decreases linearly with square root of sweep rate and attains the equilibrium capacitance at zero sweep rate. (C) The Author(s) 2015. Published by ECS. All rights reserved
Morphological changes with electrode potential in microtubules and nanowires of Polyaniline: an in-situ EC-AFM study
No full textPolyaniline (PANI) changes its conformation and conductivity on alteration of its electrochemical state. In the present work, we have studied the morphological changes with electrode potential in microtubules and nanowires of PANI using in-situ electrochemical AFM (EC-AFM). About 15 to 20% change in dimensions was observed on changing the electrochemical state in H2SO4 as the electrolyte. Such changes in microtubules and nanowires of PANI may find useful applications in actuation and sensing
Immobilization of antibodies on polyaniline films and its application in a piezoelectric immunosensor
No full textConducting polymers, especially polyaniline (PAni), have been extensively used in biosensor applications. A protocol for covalent immobilization of human IgG on polyaniline using glutaraldehyde as the cross-linker is described in this report and utilized in development of a piezoelectric immunosensor. Here, PAni was used as the substrate for immobilization. The electropolymerization parameters were optimized to get suitable thickness and surface morphology of the PAni for obtaining high density and uniformity of immobilized antibodies on the surface of our films. Possible reaction between PAni thin films and glutaraldehyde was explored using FT-IR characterization in grazing angle mode and XPS. The protocol has been characterized with the help of quartz crystal microbalance analysis. An antibody surface density of 4.86 ng/ mm(2) was obtained. A piezoelectric biosensor developed for detection of IgG with the proposed protocol was capable of differentiating the target analyte concentrations between 500 ng/ mL and 25 mu g/mL with nonspecific binding of similar to 10%
FORMIC-ACID OXIDATION AT PLATINIZED PLATINUM-ELECTRODES .5. FURTHER STUDY OF CATALYTIC EFFECT OF PREADSORBED SULFUR
No full textOXIDATION OF FORMIC-ACID AT PLATINUM MICROPARTICLES DISPERSED IN A POLYANILINE MATRIX - INFLUENCE OF LONG-RANGE ORDER AND METAL-POLYMER INTERACTION
No full textA study of polyaniline microtubules: Toward superior transducing abilities
No full textPolyaniline grown into pores of polycarbonate membrane has been shown to behave like a microelectrochemical transistor. The nature of the polycarbonate membrane results in a fraction of the polyaniline growing in an ordered and compact fashion along the walls of the pore. The switching properties of polyaniline grown into such pores changes significantly when the polycarbonate membrane is treated with a surfactant like Triton X 100. The polyaniline obtained in this case is largely disordered and open, with room for changes in conformation. This disordered material therefore shows larger changes in conductivity, about a factor of 10(2) larger, than the ordered material on switching from insulating to conducting state
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