Streaming potential, instruments commercial

The potential of macroscopic grains can be conveniently measured by electroosmosis, A few commercial instruments are available, and many home made designs have been described in literature [52], The apparatus described in Ref. [53] requires samples in form of two flat disks about 50 mm in diameter one of which has a central hole 6 ram in diameter to measure radial flow streaming potential. 

An introduction to electrokinetic phenomena can be found in [240] and in handbooks of colloid chemistry. The choice of method and instrument suitable for the character of a sample is key to successful electrokinetic measurements. In principle, all techniques and all instruments should produce the same potential and the same IEP in a system of interest. A few multi-instrument studies have been published. For example, [241] reports lEPs obtained by streaming potential and by electrophoresis (using a commercial apparatus). A multi-instrument electrokinetic study of alumina in O.OIM NitNO, is reported in [242]. The IEP was also relatively consistent with different solid-to-liquid ratios. Glass capillaries with inner sides coated with spherical nanosize hematite particles showed an IEP at pH = 5, while the IEP of the original hematite obtained by electrophoresis was at pH 9.3 [243]. 

When the solid phase is fixed (e.g., as a capillary, membrane, or porous plug), a forced flow of liquid induces an electric field. The potential difference is sensed by two identical electrodes. The streaming potential or streaming current can be used to determine the potential. The streaming potential and electro-osmosis can be observed in similar experimental setups, except that the natures of the force and the flux are reversed. Thus, the recommendations and limitations discussed in Section 2.1.2 also apply to measurements based on the streaming potential. For example, the instrument cell induces a streaming potential, which may contribute substantially to the result of the measurement. A linear dependence between the potential obtained by electrophoresis and the streaming current measured by a commercial apparatus was observed in... 

The tables in Chapter 3 report results obtained using the following commercial instruments based on streaming potential ... 

Streaming potential was measured using a Brookhaven Instruments Corp. (Holtsville, NY, USA) BI-EKA commercial instrument which has a crossflow slit geometry. Childress and Elimelech (1996) and Elimelech et al. (1994) described the measuring cell and the principle in detail. For comparison, another surface potential analyser was used as constructed and described by Pihlajamaki (1998). The streaming potential, from which the zeta potential can be calculated with the Helmholtz-Smoluchowski equation, was measured in the presence of 10 mM NaCl, 1 mM NaHCO s and 0.5 mM CaCh, unless otherwise... 

A streaming current detector based on a completely different principle than the above instruments is presented in [299], The dispersion is in a narrow space between a vertical cylindrical vessel and a coaxial piston, which moves back and forth along the axis. The potential between two gold electrodes on the wall of the cylinder at different heights is measured, and its zero value is identified with the IEP. The apparatus own response corresponds to the electrokinetic behavior of the piston and cell materials. In the presence of a colloid, the piston and the cell are assumed to be covered with colloidal particles. The above design has been utilized in some commercial instruments ... 

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