Zeta potential cuvettes - Omega vs U-shaped

Zeta potential is a key indicator of colloidal stability. When a colloid has high zeta potential (highly positive OR highly negative), the colloidal particles tend to repel each other, so the chance of agglomeration is low. A low zeta potential, on the other hand, may lead to aggregation due to the low repelling forces between the particles. Thus, zeta potential is an important factor for the preparation, storage and break-down of colloidal dispersions across diverse industries, such as biomedical technology, polymers, paper, paints and coatings, and pharmaceuticals.

Zeta potential can be conveniently determined by using electrophoretic light scattering (ELS), in which the electrophoretic mobility is measured, and then used to calculate the zeta potential. A cuvette containing a capillary channel is filled with the sample to be measured. When a potential difference is applied at each end of the channel, the particles are induced to move towards the oppositely charge electrode. A laser beam irradiates the dispersion and is then scattered by the particles in the dispersion. The frequency of the scattered light is shifted proportionally to the particles' movement, so the electrophoretic mobility can be obtained from the shift (Doppler shift). The zeta potential can then be calculated from the electrophoretic mobility by using the Smoluchowski/Hückel approximation. ELS measurements are easy to automate and highly reproducible, even with complex samples.

Nonetheless, one issue is that the zeta potential is generally measured at a part of the tube that is slightly curved, which can lead to a gradient in the strength of the electric field. Such a gradient means that the measured zeta potential strongly depends on the measurement position within the cuvette.

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