Home About us Contact
The Influence of Electrode Porosity on Diffusional Cyclic VoltammetryELECTROANALYSIS, Issue 22 2008
Abstract A simple generic model to predict the influence of electrode porosity on the cyclic voltammetric response of an electrode is presented. The conditions under which deviation from the behavior of a perfectly flat, planar electrode can be expected are predicted. The scope for misinterpretation when conventional flat electrode theory is applied to porous electrodes is highlighted, especially in respect to the extraction of electrode kinetic parameters and the influence of ,electrocatalysis'. [source]
A Contactless Impedance Probe for Simple and Rapid Determination of the Ratio of Liquids with Different Permittivities in Binary MixturesELECTROANALYSIS, Issue 1 2009
Franti, ek Opekar
Abstract Simple contactless cells with planar or tubular electrodes have been designed for measurement of the permittivity of solutions. The cells, connected to an integrated circuit of astable multivibrator, respond primarily to the capacitance component of the cell impedance, the multivibrator frequency depends in a defined manner on the solution permittivity and is readily used as the analytical signal in determinations of the ratios of components in binary liquid mixtures; water solution of methanol, ethanol and dioxane have been tested. The response of the cell with planar electrodes satisfies well the simple theoretical model and both the cells provide results with a sufficient sensitivity, a low LOD value (units of %vol) and a good precision (around 1%rel). The cell simplicity, small dimensions, long-term stability and the possibility of powering them from a battery make them suitable for hand-held meters. As an example of application in practice, the content of ethanol was determined in the car fuel petrol. [source]
A 3-D dielectrophoretic filter chipELECTROPHORESIS, Issue 7 2007
Ciprian Iliescu Dr.
Abstract The paper presents a 3-D filter chip employing both mechanical and dielectrophoretic (DEP) filtration, and its corresponding microfabrication techniques. The device structure is similar to a classical capacitor: two planar electrodes, made from a stainless steel mesh, and bonded on both sides of a glass frame filled with round silica beads. The solution with the suspension of particles flows through both the mesh-electrodes and silica beads filter. The top stainless steel mesh (with openings of 60,,m and wires of 30,,m-thickness) provides the first stage of filtration based on mechanical trapping. A second level of filtration is based on DEP by using the nonuniformities of the electric field generated in the capacitor due to the nonuniformities of the dielectric medium. The filter can work also with DC and AC electric fields. The device was tested with yeast cells (Saccharomyces cerevisae) and achieved a maximal trapping efficiency of 75% at an applied AC voltage of 200,V and a flow rate of 0.1,mL/min, from an initial concentration of cells of 5×105 cells/mL. When the applied frequency was varieted in the range between 20 and 200,kHz, a minimal value of capture efficiency (3%) was notticed at 50,kHz, when yeast cells exhibit negative DEP and the cells are repelled in the space between the beads. [source]
Numerical comparison between Maxwell stress method and equivalent multipole approach for calculation of the dielectrophoretic force in single-cell trapsELECTROPHORESIS, Issue 11 2005
Abstract This paper presents detailed numerical calculations of the dielectrophoretic force in traps designed for single-cell trapping. A trap with eight planar electrodes is studied for spherical and ellipsoidal particles using the boundary element method (BEM). Multipolar approximations of orders one to three are compared with the full Maxwell stress tensor (MST) calculation of the electrical force on spherical particles. Ellipsoidal particles are also studied, but in their case only the dipolar approximation is available for comparison with the MST solution. The results show that a small number of multipolar terms need to be considered in order to obtain accurate results for spheres, even in the proximity of the electrodes, and that the full MST calculation is only required in the study of nonspherical particles. [source]
A General Electrochemical Strategy for Synthesizing Charge-Transfer Complex Micro/NanowiresADVANCED FUNCTIONAL MATERIALS, Issue 8 2010
Abstract Universal strategies for synthesizing one-dimensional organic nanomaterials are of fundamental importance in the development of more flexible, cheaper and lighter electronics. Charge-transfer (CT) complexes, the major kind of organic conductors, are in the long-term attractive materials owing to their unique crystal structures and conductive properties. In this article, a general strategy for the synthesis of CT complex micro/nanowires based on the localized nanoelectrochemistry using tiny carbon nanotube (CNT) electrodes is presented. This strategy is successfully demonstrated over 12 typical CT complexes, and a general rule for the preparation of various kinds of CT complex micro/nanowires is summarized. The CT complex micro/nanowires thus synthesized have high aspect ratios and long lengths as compared with traditional macroscopic planar electrodes, originating from the one-dimensional structural feature with fewer or no defects and the ultrasmall surface area of the CNT. This work provides a more versatile material basis for the fundamental and application studies of low-dimensional organic conductor materials. [source]
Linear Dichroism in the XANES of Partially Oriented Samples: Theory and Application to the Photosynthetic Manganese Complex,CHEMPHYSCHEM, Issue 6 2010
Peter Liebisch Dr.
Abstract For molecular systems which are partially ordered with respect to one macroscopic axis, for example, the sample,surface normal, X-ray absorption spectroscopy (XAS) with linearly polarized synchrotron radiation can provide information on structure and orientation of the X-ray absorbing site (polarized or linear-dichroism XAS). Examples for such partially oriented systems are protein-carrying membrane particles deposited in the form of multilayers on surfaces, layered minerals, surface films or imperfect 2D crystals, planar electrodes or catalytic surfaces. For electric dipole transitions, equations are derived describing how partial unidirectional orientation determines the linear dichroism (LD). The approach presented facilitates description of 1) LD in multiple-scattering contributions of the extended X-ray absorption fine-structure (EXAFS) and 2) of LD in the X-ray absorption near-edge structure (LD-XANES). Structural and orientation information becomes accessible by combination with ab initio XANES calculations. The LD-XANES approach is applied to the water-oxidizing Mn complex of photosystem II. The results suggest that the (,-O)-(,-O) vectors of the Mn-(,-O)2 -Mn units are at an average angle to the membrane normal of 30,45°. The best-fit structure in connection with crystallographic data suggests a specific oxidation-state assignment: Mn(1)IIIMn(2)IIIMn(3)IVMn(4)IV. However, currently this assignment remains uncertain. In future studies, the LD-XANES analysis should play an important role in construction of unequivocal atomic-resolution model of the photosynthetic Mn complex. [source]