A remarkable change in the conductivity of a polyaniline (PAN) Langmuir monolayer in the conducting state, as a function of surface pressure, has been observed using scanning electrochemical microscopy (SECM). The film conductivity, as expressed by the SECM current response of a redox mediator, was measured in-situ in a Langmuir film balance. The conductivity of the film increases significantly with surface pressure, above a threshold value of ca. 20 mN m-1.[on SciFinder (R)]

The applicability of thin sol-gel films as selective interfaces in electrochem. sensors has been examd. This requires not only to create a selective interface but also to enable facile diffusion of the analytes across the films. Creation of selectivity has been aimed by molecularly imprinting an electroactive species in the course of sol-gel formation. We have focused primarily on imprinting an iron(II) complex, i.e., tris(2,2'-bipyridine)iron(II) (Fe(bpy)2+3), as a means of selectively detg. iron(II) in aq. soln. Hence, the effect of different parameters, such as the compn. of the sol-gel film and the hydrolysis and drying time, on the diffusion of Fe(bpy)2+3, has been studied. We find that diffusion can be remarkably enhanced upon adding polyethylene glycol or a surfactant, such as decanoic acid. Nevertheless, so far we have not been able to develop thin films, which exhibit selectivity towards this inorg. species. The difficulties in designing such selective interfaces for heavy metals as opposed to org. species is demonstrated by successfully applying the same approach for designing a selective interface for diethyl-p-nitrophenyl phosphate (paraoxon). [on SciFinder(R)]

A remarkable change in the cond. of a polyaniline (PANI) Langmuir monolayer in the conducting state, as a function of surface pressure, was obsd. using scanning electrochem. microscopy (SECM). The film cond., as expressed by the SECM current response of a redox mediator, was measured in-situ in a Langmuir film balance. The cond. of the film increases significantly with surface pressure, above a threshold value of ca. 20 mN m-1. [on SciFinder(R)]

The application of self-assembled monolayers (SAMs) as a means of achieving speciation in heavy metal electrochem. detn. is demonstrated. SAMs are monomol. org. layers that can be chem. attached onto different electrode materials and used for the selective extn. of heavy metals. The selectivity is achieved by assembling monolayers that have pendant ligands, which interact selectively with the analytes in the soln. For example, the formation of a monolayer comprising a pyridine group was used to selectively ext. Cr(VI) from aq. solns., whereas the selective detn. of Fe(II) was accomplished using a covalently bound terpyridine monolayer. Yet, detg. the heterogeneous binding consts. of the metallic species by the SAMs is of significant importance and allows studying quant. the interactions between the monolayer and the metal ions. The authors have developed a few methods for detg. the binding consts. of heavy metal ions by SAMs of which two of them are briefly discussed here. [on SciFinder(R)]

The local injection and lateral propagation of charge in ultrathin polyaniline (PAN) layers were studied with the scanning electrochem. microscope (SECM). Monolayers of PAN were deposited on a glass substrate using the LB method and were chem. reduced using Na dithionite. A microelectrode held close to the PAN layer was used to generate a flux of an oxidant, i.e., Fe(phen)33+ (phen = 1,10-phenanthroline) which diffused to the surface and locally oxidized the reduced PAN. By simulating the current-time transients, the kinetics of lateral charge propagation were evaluated. [on SciFinder(R)]

Electron transfer processes at tungsten oxide films prepd. by the sol-gel method were investigated and characterized by scanning electrochem. microscopy (SECM) and cyclic voltammetry. The feedback mode of the SECM was used for studying the localization and mechanism of the heterogeneous charge transfer at tungsten oxide thin films, which were deposited on conducting, i.e., tin oxide, and insulating substrates. Investigating the feedback current as a function of the mediator concn., thickness of the tungsten oxide film and the nature and concn. of the electrolyte, allow detn. of the rate limiting step and cond. of the film. [on SciFinder(R)]

The adsorption of thiols on different metal surfaces has been studied using potentiometric measurements. The adsorption is a complex process that comprises a few steps. The first involves neg. charge transfer to the electrode surface as evidenced by a sharp neg. shift of the open circuit potential (ocp). The charge that is accumulated on the electrode surface is discharged through a redn. process that involves either water or oxygen redn. The rate of the discharging process depends strongly on the overpotential of the electrode material for water redn., the medium, and to some extent, on addnl. functional groups that the thiol bears. A detailed general mechanism that is in agreement with our findings is proposed and discussed. [on SciFinder(R)]

Sol-gel films were electrodeposited on Al electrodes following the methodol. the authors have developed and is based on applying neg. potentials. This increases the pH at the surface, causing acceleration of the polymn. The authors' process follows the two step method, in which the monomer is 1st hydrolyzed in acidic soln. (pH ∼ 4) and only then the neg. potential is applied, which consumes protons and releases hydroxyl ions, thus enhancing the condensation. Films made of different monomers, i.e., tetraethoxysilane (TEOS), Me trimethoxysilane and Ph trimethoxysilane (PTMOS), were prepd., characterized and examd. for their corrosion inhibition properties. Potentiodynamic polarization, electrochem. impedance spectroscopy, optical and SEM as well as at. force microscopy were used as a means of film characterization. Hydrophobic and steric silanes, such as PTMOS showed a considerable corrosion inhibition capacity as compared to the capacity exhibited by less hydrophobic and steric derivs. such as TEOS. The difference between the conventional dip-coating method and the electrodeposition approach for depositing sol-gel films was also examd., indicating a clear advantage of the latter. [on SciFinder(R)]