Determination Of Surface Charge Density Research Articles

Time-resolved pressure-induced electric potential in nanoporous membranes: Measurement and mechanistic interpretation

Performance of charged nanoporous membranes in ion separations and electrokinetic energy conversion is controlled by their surface-charge density. This (or related such as zeta-potential) parameter has often been obtained from measurements of pressure-induced electric potential typically referred to as streaming potential. However, with nanoporous membranes in dilute electrolyte solutions, determination of genuine streaming potential is non-trivial and requires time-resolved measurements. A new approach to the interpretation of such measurements developed and tested experimentally in this study makes possible parallel determination of several membrane transport properties while previously only streaming-potential coefficient was determined. In nanoporous membranes, this coefficient is a non-monotone function of surface-charge density, which makes difficult unambiguous determination of the latter. On the contrary, the other properties determined in this study are monotone functions of surface-charge density. This approach has been validated via characterization of two nanoporous track-etched membranes (with the pore sizes of 25 nm and 35 nm) in KCl solutions and revealed an excellent applicability. The transport properties “extracted” from experimental data were used as input of full (numerical) version of space-charge model. This made possible determination of surface-charge density as well as some properties of hypothetical gel layers reportedly surrounding pores of nanoporous grades of track-etched membranes.

Characterization and determination of surface charge density of a polymer latex

Potentiometric and conductometric titrations were carried out to get information on the surface charge density of styrenebutyl acrylate copolymer latex. It was established that there are two types of acidic groups present in the polymer latex particles. The effect of electrolyte concentration on the stability of the latex was studied. The values of the critical coagulation constant for the polymer latex have been investigated. Potentiometrische und konduktometrische Titrationen wurden durchgeführt, um Informationen über die Oberflächenladungsdichte eines Styren-Butylacrylat-Copolymer-Latex zu erhalten. Es wurde festgestellt, daß in den Latexteilchen zwei Arten von sauren Gruppen vorhanden sind. Der Einfluß der Elektrolytkonzentration auf die Stabilität des Polymerlatex wurde untersucht. Die Werte der kritischen Koagulationskonstanten des Latex wurden bestimmt.

A dropping mercury microelectrode (DMμE) for the direct determination of surface charge densities

A dropping mercury electrode has been constructed which produces drops with a radius of about 50 μm. The characteristics of such electrodes are similar to those of conventional electrodes except for the strongly reduced natural drop time. This drop time turns out to be very stable and virtually independent of surface tension. These properties allow for interesting applications. Here the electrode is used for the determination of electrode surface charge density, which proves to be quite accurate. Because this technique has distinct advantages over the currently available ones we consider it to be a powerful tool in double-layer research.

Determination of surface charge density of soils

Abstract A simple and precise method for determination of surface charge density of soils is described. It involves saturating the negative and positive exchange sites with NH+ 4 and NO‐ 3 ions, respectively, removing the excess solution by centrifugation, and determining the ions on the exchange sites by a steam distillation method. Results showed that the concentration and type of saturating ions and the extractant used significantly affected the surface negative charge densities. The average value of surface negative charge densities of 10 surface soils from Iowa, Chile, and Costa Rica by the proposed method agreed closely with that obtained by the original method proposed by Schofield in 1949 (14.6 vs. 13.7 cmol(‐) kg‐1 soil). The advantages of the proposed method are no need for the laborious extraction steps and simplicity of the steam distillation method for determination of NH+ 4 and NO‐ 3 in soil samples.

Determination of surface charge density of dispersed oxidic particles in aqueous solutions by a coulometric method

Determination of surface charge density of dispersed oxidic particles in aqueous solutions by a coulometric method