Mini-Encyclopedia of Papermaking Wet-End
Part Two: Definitions and Concepts
The streaming current method is one of the most widely used means of detecting the endpoint of a charge demand titration. The mechanical parts of the device are very simple. A plastic piston moves up and down about four times per second within a closely-spaced plastic cylinder. Two electrode probes contact the solution near the closed bottom of the cylinder and at the top, where the cylinder widens out into a chamber. The piston motion causes a much more rapid reciprocal motion of aqueous fluid (the sample) within the annulus. The flowing liquid carries along any counter-ions that lie outside of the hydrodynamic slip plane at the plastic surfaces. The circuit of this current is completed and measured in an external connection and electronic device between the two electrode probes. During an evaluation of colloidal charge of an aqueous sample one adds an oppositely charged titrant until the signal goes to zero. In theory, this condition occurs when neutral complexes between the titrant and components of the sample become less soluble and cover the probe surfaces.
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