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)]

A new approach to micropatterning is demonstrated. The approach is based on driving an electrochemical process at the solid-liquid interface through the formation of a flux of ions from a micropipet that is held in close proximity to the surface. The flux of ions is generated by the so-called potential assisted ion transfer at the interface between two immiscible electrolyte solutions (ITIES). As a model system, the local deposition of silver was examined. Specifically, a constant potential, which was applied to a micropipet filled with an aqueous solution of silver ions, caused the transfer of Ag(+) into the outer nitrobenzene (NB) solution that consisted of an electrolyte, tetrabutylammonium tetrakis[4-chlorophenyl]borate (TBATPBCl). To facilitate the transfer of silver ions a macrocyclic ligand, that is, dibenzo-24-crown-8 (DB24C8), was added to the organic phase. The Faradaic current of this micro-ITIES was used as a means of controlling the tip-surface distance in scanning electrochemical microscopy (SECM) and depositing silver microstructures on a gold substrate.[on SciFinder (R)]

A new approach to micropatterning is demonstrated. The approach is based on driving an electrochem. process at the solid-liq. interface through the formation of a flux of ions from a micropipet that is held in close proximity to the surface. The flux of ions is generated by the so-called potential assisted ion transfer at the interface between two immiscible electrolyte solns. (ITIES). As a model system, the local deposition of silver was examd. Specifically, a const. potential, which was applied to a micropipet filled with an aq. soln. of silver ions, caused the transfer of Ag+ into the outer nitrobenzene (NB) soln. that contained an electrolyte, tetrabutylammonium tetrakis[4-chlorophenyl]borate (TBATPBCl). To facilitate the transfer of silver ions a macrocyclic ligand, i.e., dibenzo-24-crown-8 (DB24C8), was added to the org. phase. The faradaic current of this micro-ITIES was used as a means of controlling the tip-surface distance in scanning electrochem. microscopy (SECM) and depositing silver microstructures on a gold substrate. [on SciFinder(R)]

The affinity of selected metal ions for palmitic (PAL) and hexadecanesulfonic acid (HDSA) monolayers self-assembled onto an octadecyl silane (ODS) monolayer covalently bound to a Ge internal reflection element has been examd. in situ in aq. electrolytes by attenuated total reflection Fourier transform IR spectroscopy. Marked changes in the bands assocd. with the sym. and asym. stretches of the carboxylate groups induced by metal-ion binding could be discerned for PAL/ODS self-assembled bilayers (SABs) in contact with Cd2+ solns. of pH = 6 even at concns. in the sub-μM range. Subsequent exposure of Cd2+/PAL/ODS SABs to solns. of pH < 4 devoid of Cd2+ led to the removal of Cd2+ from the bilayer leaving behind a better ordered structure, as judged by the shift of the C-H stretching modes toward lower wavenumbers. Spectral evidence for strong metal-terminal sulfonate group interactions was also obtained for HDSA/ODS SABs immersed in solns. contg. Cd2+, Fe3+, and Fe2+, for which the effects on the characteristic sym. and asym. modes of the terminal sulfonate moieties were found to be unique to the nature of each of the metal ions. [on SciFinder(R)]

High-quality self-assembled monolayers of long-chain alcs. were formed on H-terminated cryst. and porous Si surfaces under mild conditions in a 1-step reaction using iodoform as an in-situ iodinating agent. Besides the convenient conditions under which the procedure is carried out, it yields a high surface coverage and suppresses oxide formation. In-situ iodination is advantageous over other direct methods as it probably forms very reactive intermediate species, e.g. Si-I, that channel the reaction via a nucleophilic attack to form highly dense monolayers. [on SciFinder(R)]

A new approach for designing a voltammetric selective electrode is presented. The approach is based on the formation of a disorganised inert self-assembled monolayer (SAM), in which an amphiphilic molecule is incorporated. The latter serves as the selectivity factor, which extracts the analyte. The purpose of these experiments is to study the parameters that affect the capability of a monolayer to host amphiphiles. As model systems we focused on the incorporation of simple amphiphilic molecules (quaternary alkyl ammonium salts), electroactive amphiphiles (dialkylviologens) and a macrocycle ligand (tetramethylcyclam) into octadecyl silane monolayers formed on indium tin oxide (ITO) and purposely made disorganised alkanethiols on gold. We find that basically, the incorporation of amphiphiles into a hydrophobic inert SAM resembles a reversed stationary phase in liquid chromatography and this configuration can be used for designing selective electrodes.[on SciFinder (R)]

Different approaches for increasing the sensitivity and selectivity of voltammetric probes for heavy metals were examd. These have involved adsorbed monolayers of host mols., functionalized self-assembled monolayers and thin polymeric films. Two systems are presented that focus on the selective anal. of Hg(II) and Fe(II). The electrode for Hg(II) is based on a macrocyclic ligand, i.e., Kryptofix-222, while that for Fe(II) relies on the selective complexation by ferroin ligands, such as 1,10-phenanthroline. The monomeric and polymeric approaches were examd. and compared for both systems. The principal aim of this manuscript is to highlight the ability of fine-tuning the selectivity characteristics of the solid-liq. interface as a result of considering and optimizing analyte-interface interactions. Basically, an interface comprising a monolayer, which is capable of forming a strong and selective complex with the analyte, is likely to exhibit sensitivity that is at least as good as a polymeric film. However, the stability and durability of the latter usually makes it a superior interface for repetitive anal. and will therefore be the preferred choice for flow anal. systems. [on SciFinder(R)]

A new approach for designing a voltammetric selective electrode is presented. The approach is based on the formation of a disorganized inert self-assembled monolayer (SAM), in which an amphiphilic mol. is incorporated. The latter serves as the selectivity factor, which exts. the analyte. The purpose of these expts. is to study the parameters that affect the capability of a monolayer to host amphiphiles. As model systems the authors focused on the incorporation of simple amphiphilic mols. (quaternary alkyl ammonium salts), electroactive amphiphiles (dialkylviologens) and a macrocycle ligand (tetramethylcyclam) into octadecyl silane monolayers formed on In Sn oxide (ITO) and purposely made disorganized alkanethiols on Au. Basically, the incorporation of amphiphiles into a hydrophobic inert SAM resembles a reversed stationary phase in liq. chromatog. and this configuration can be used for designing selective electrodes. [on SciFinder(R)]

A disposable heating unit for use for heating the contents of a container, includes a first region contg. a combination of at least two solid substances which undergo an exothermic chem. reaction which is not spontaneous at room temp. Adjacent to the first region is a second region contg. at least a first reagent. A storage cell is configured for releasing the liq. contg. a second reagent into the second region. The first and second reagents undergo a spontaneous exothermic chem. reaction when brought into contact, thereby initiating the exothermic chem. reaction of the solid substances. [on SciFinder(R)]

A review with refs. of self-heating beverage containers. [on SciFinder(R)]

The scanning electrochem. microscope was applied in the feedback mode to deposit Au microstructures on n-Si(111) and indium-tin oxide. This was accomplished by the anodic dissoln. of Au at the microelectrode followed by the subsequent redeposition of the Au on the substrate. The influence of pH, substrate potential, and deposition time on the cryst. nanometer structure of the micrometer Au deposits was studied. The effect of these parameters on deposition could be explained by the band structure of the silicon. Also, understanding the role played by the different parameters allows depositing predefined nanocryst. structures. [on SciFinder(R)]

A highly flexible, automatic sequential-injection stripping anal. (SISA) system was developed and applied for monitoring the levels of Hg in aq. solns. using a chem. modified electrode. The prepn. of the modified electrode comprises spin coating of an EtOH soln. of poly(4-vinylpyridine) and Kryptofix-222 onto a glassy C electrode (GCE) followed by crosslinking the polymer. The anal. is based on the anodic stripping voltammetry of Hg using differential pulse voltammetry. A sequence of 36 operations was needed to complete a full cycle of cleaning, calibration and anal. [on SciFinder(R)]

A monolayer of conducting polymer, polyaniline (PAN), was assembled on hydroxyl-terminated surfaces, such as quartz, glass, indium-tin oxide, and native oxide on Si. The approach for assembling two-dimensional monolayers of PAN is based on a chem. or electrochem. surface polymn. of electrostatically bound anilinium. The latter was bound to the neg. charged sulfonate group of mercaptoethanesulfonate that was previously coupled by an SN2 reaction to an iodopropyl self-assembled monolayer. The consecutive assembling steps were followed by XPS, UV-vis-NIR spectroscopy, variable angle spectroscopic ellipsometry, contact angle, and at. force microscopy measurements. The characteristic electronic properties of the PAN monolayers were studied by UV-vis-NIR spectroscopy and cyclic voltammetry. [on SciFinder(R)]

The prepn. and characterization of octadecylsilane, C18, monolayers on indium-tin oxide (ITO) were studied carefully. A reproducible procedure was developed for the formation of C18/ITO employing octadecyltrimethoxysilane (OTMS) as a monomer. The films were studied by electrochem., wettability, IR and at. force microscopy. All these measurements provide evidence for the formation of a disorganized, 'brush-type' monolayer with a max. surface fractional coverage of 0.90 ± 0.04. The surface coverage can be controlled through the silanization time. The applications and implications of such disorganized monolayers in electroanal. chem. are discussed. [on SciFinder(R)]