Petr Vanysek

Communications: Monovalent ion condensation at the electrified liquid/liquid interface

X-ray reflectivity studies demonstrate the condensation of a monovalent ion at the electrified interface between electrolyte solutions of water and 1,2-dichloroethane. Predictions of the ion distributions by standard Poisson-Boltzmann (Gouy-Chapman) theory are inconsistent with these data at higher applied interfacial electric potentials. Calculations from a Poisson-Boltzmann equation that incorporates a nonmonotonic ion-specific potential of mean force are in good agreement with the data.

X-ray studies of the interface between two polar liquids: neat and with electrolytes

We demonstrate the use of X-ray reflectivity to probe the electron density profile normal to the interface between two polar liquids. Measurements of the interfacial width at the neat nitrobenzene/water and the neat water/2-heptanone interfaces are presented. These widths are consistent with predictions from capillary wave theory that describe thermal interfacial fluctuations determined by the tension and bending rigidity of the interface. Variation of the temperature of the water/nitrobenzene interface from 25 degrees C to 55 degrees C indicates that the role of the bending rigidity decreases with increasing temperature. X-ray reflectivity measurements of the electrified interface between an aqueous solution of BaCl2 and a nitrobenzene solution of TBATPB demonstrate the sensitivity of these measurements to the electrolyte distribution at the interface. A preliminary analysis of these data illustrates the inadequacy of the simplest, classical Gouy-Chapman theory of the electrolyte distribution.

Impedance and voltammetric studies of electrogenerated polyaniline conducting films

Abstract Polyaniline thin films were electrochemically synthesized from aniline in three acids: sulfuric, hydrochloric and perchloric. Cyclic voltammetry was used in the electrosynthesis, and the relationship of voltammetric parameters the properties of the conductive form of the films were investigated. The main tool for film characterization was impedance spectroscopy. Semi-automated plotting of three-dimensional Argand diagrams with a potential parameter was used for synoptic view of the system and nonlinear least-square data fitting was used for rigorous treatment. Charge storage capacity, resistance and changes in constant phase element parameters were analyzed in relation to the use of the three acidic media.

Ion Distributions at the Water/1,2-Dichloroethane Interface: Potential of Mean Force Approach to Analyzing X-ray Reflectivity and Interfacial Tension Measurements

We present X-ray reflectivity and interfacial tension measurements of the electrified liquid/liquid interface between two immiscible electrolyte solutions for the purpose of understanding the dependence of interfacial ion distributions on the applied electric potential difference across the interface. The aqueous phase contains alkali-metal chlorides, including LiCl, NaCl, RbCl, or CsCl, and the organic phase is a 1,2-dichloroethane solution of bis(triphenylphosphor anylidene) ammonium tetrakis(pentafluorophenyl)borate (BTPPATPFB). Selected data for a subset of electric potential differences are analyzed to determine the potentials of mean force for Li(+), Rb(+), Cs(+), BTPPA(+), and TPFB(-). These potentials of mean force are then used to analyze both X-ray reflectivity and interfacial tension data measured over a wide range of electric potential differences. Comparison of X-ray reflectivity data for strongly hydrated alkali-metal ions (Li(+) and Na(+)), for which ion pairing to TPFB(-) ions across the interface is not expected, to data for weakly hydrated alkali-metal ions (Rb(+) and Cs(+)) indicates that the Gibbs energy of adsorption due to ion pairing at the interface must be small (<1 k(B)T per ion pair) for both the CsCl and RbCl samples. This paper demonstrates the applicability of the Poisson-Boltzmann potential of mean force approach to the analysis of X-ray reflectivity measurements that probe the nanoscale ion distribution and the consequences of these underlying distributions for thermodynamic studies, such as interfacial tension measurements, that yield quantities related to the integrated ion distribution.

Effect of Zinc and Iron Ions on the Electrochemistry of Nickel Oxide Electrode: Slow Cyclic Voltammetry

Abstract Porous nickl oxide electrodes were prepared by cathodic electroprecipitation from metal nitrate solutions on sintered substrate and characteristics by slow (0.1 m V/s) voltammetry in 6 mol/1 KOH. The presence of iron or zinc ions added to the electrolyte after formation of the electrodes resulted in a decrease of electrode charging ability. Removal of iron or zinc ions and presence of lithium ions partially restored the voltammogram to original conditions. Presence of cobalt in the electrode material diminished substantially the influence of zinc ions on the electrode properties.

Electrochemical determination of lead and lead ion transfer at liquid-liquid interfaces

Abstract The transfer behavior of lead (II) ion at a liquid-liquid interface, facilitated by neutral carriers (polyethylene glycols), is studied by an electrochemical method. The transfer process is discussed in terms of the formation of complexes in two phases and attributed to the transfer of a complex ion across the interface. The apparent standard transfer potential, ΔwoφPbL2+o, apparent standard Gibbs energy of transfer, ΔwoGPbL2+o, and the dissociation constant of the complex, KPbL2+, in the aqueous phase are obtained from the experimental data. The results suggest a new electrochemical method for the determination of lead.

Transport of Zn ( OH ) 4 2 − Ions across a Polyolefin Microporous Membrane

Transport of Zn(OH) 4 2+ ions through modified microporous polypropylene membranes (Celgard 3401, 3501) was studied using polarography and conductometry. Soluble Nafion as an ion exchange modifying agent was applied to the membrane by several techniques. The influence of Nafion and a surfactant on transport of zinc ions through the membrane was studied. A relationship between membrane impedance and the rate of Zn(OH) 4 2- transport was found. The found correlation between conductivity, ion permeability, and Nafion coverage suggests a suitable technique of membrane preparation for obtaining the desired zinc ion barrier properties

Electric Field Effect on Phospholipid Monolayers at an Aqueous–Organic Liquid–Liquid Interface

The electric potential difference across cell membranes, known as the membrane potential, plays an important role in the activation of many biological processes. To investigate the effect of the membrane potential on the molecular ordering of lipids within a biomimetic membrane, a self-assembled monolayer of 1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine (SOPC) lipids at an electrified 1,2-dichloroethane/water interface is studied with X-ray reflectivity and interfacial tension. Measurements over a range of electric potential differences, -150 to +130 mV, that encompass the range of typical biomembrane potentials demonstrate a nearly constant and stable structure whose lipid interfacial density is comparable to that found in other biomimetic membrane systems. Measurements at higher positive potentials, up to 330 mV, illustrate a monotonic decrease in the lipid interfacial density and accompanying variations in the interfacial configuration of the lipid. Molecular dynamics simulations, designed to mimic the experimental conditions, show that the measured changes in lipid configuration are due primarily to the variation in area per lipid with increasing applied electric field. Rotation of the SOPC dipole moment by the torque from the applied electric field appears to be negligible, except at the highest measured potentials. The simulations confirm in atomistic detail the measured potential-dependent characteristics of SOPC monolayers. Our hybrid study sheds light on phospholipid monolayer stability under different membrane potentials, which is important for understanding membrane processes. This study also illustrates the use of X-ray surface scattering to probe the ordering of surfactant monolayers at an electrified aqueous-organic liquid-liquid interface.

Quartz crystal microbalance in electroanalytical applications

Electrochemistry research and to a lesser degree its applications, have embraced the quartz crystal microbalance as a useful tool, because this device can operate while immersed in a liquid and because the crystal metal surface can serve simultaneously as an electrode. In the following treatment three issues of electrochemical QCM work are addressed. (1) A comparison of charge and mass changes, leading to the determination of a general formula of a formed metal oxide. An example using formation of palladium oxide formed directly by electrochemical means on the QCM surface is given. (2) Application of QCM sensing device in measurement of changes of interfacial tension between two immiscible electrolyte solutions (ITIES). (3) Additional information about the QCM surface can be obtained if a network analyzer is used to probe the piezoelectric device, instead of obtaining only the crystal resonant frequency. A response of a crystal exposed to air, water and nitrobenzene, and a bare crystal and a crystal covered with polyaniline film is given.

ELECTRODIC POLYMER MATERIALS BASED IN ANILINE: INFLUENCE OF Ni2+, Co2+, AND Cu2+ IONS ON ITS FORMATION

Behaviour of aniline when voltametrically electropolymerized in the presence of Ni2+, Co2+, and Cu2+ cations has been studies 0.1 mol ·L-1 aniline in the presence of 0.01 mol·L-1 copper(II), nickel(II), and cobalt(II) ions and of three inorganic acids: HCl, HNO3, and H2SO4, was used. Aniline shows that polymerizes in all strong acids and metal ions selected, the reversibility and clarity of the redox processes in the presence of metal ions, indicate that the most accurate conditions for electrosynthesizing polyaniline (Pani) was CuCl2 in 1.0 M HCl; Ni(NO3)2 in 1.0 M HNO3 and in HNO3 1.0 M Co(NO3)2. In all cases, similar voltamograms were obtained and polymer growing changes according to the metal ion used. For Co(II), is more favorable in the following order: H2SO4 > HCl > HNO3. For Ni(II) is H2SO4 > HCl @ HNO3, and for Cu(II) is H2SO4 > HCl @ HNO3. The aim of this work is to study the effects of metal ions on aniline and their electropolymerization in acid media