Electro-Osmotic Flow for Surface Zeta Potential Analysis: Technological Background and Physical Limitations
In recent years the principle of monitoring the electro-osmotic flow (EOF) at the interface of a planar solid sample and a surrounding particle dispersion received increasing attention. The suggested benefit of EOF mapping is the combination of particle characterization (size, zeta potential) with surface zeta potential analysis in a single instrument. However, the apparent simplicity of EOF mapping hides the physical and technical challenges that limit the reliability and applicability of this method. With this whitepaper we address these challenges and compare our experience with other researchers, who evaluated the quality of zeta potential results obtained by both EOF mapping and streaming potential measurement.
The zeta potential at the solid-liquid interface may be assessed by the measurement of different electrokinetic effects, whose applicabilities depend on the size of the solid sample. Anton Paar supports the most established methods of the measurement of the electrophoretic mobility for particle dispersions and emulsions (electrophoretic light scattering with Litesizer 500) and of the measurement of the streaming potential and the streaming current for samples of macroscopic size such as granular media, fibers, porous bodies, and flat surfaces (with SurPASS 3).
For selected materials and conditions, other electrokinetic effects may be employed to determine the zeta potential, which are the electrosonic amplitude or the colloidal vibration potential (a.k.a. as electroacoustics) for dispersions of particles with a density significantly higher than the dispersant (commonly water), and the electro-osmotic flow at the solid-liquid interface, which is regarded as an artifact in the measurement of electrophoretic mobility.
The principle of the electro-osmotic flow (EOF) has gained interest in the past years due to the possibility to combine particle size measurement with the zeta potential analysis for both particles and solid samples in a single instrument. However, zeta potential results obtained by the EOF method that are reported in the literature either show a significant measuring error[2,3] or require validation by a parallel measurement of the streaming potential.
The purpose of this whitepaper is to discuss the challenges of the EOF method and to identify the measurement parameters that limit its applicability for the surface zeta potential analysis.
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