The Zeta Potential Measurement
The Nicomp DLS system also measures the zeta potential of dispersions. The zeta potential is a measure of the charge on the surface of a particle. A high zeta potential is an indicator/predictor of higher dispersion stability, and hence shelf life.
The charge (positive or negative) is not important, just the magnitude of the charge. Zeta potential is also used to determine the iso-electric point (IEP) of a dispersion – the pH where the zeta potential is zero.
The IEP provides information about the worst conditions for stability and also about the predominant chemical species at the surface of engineered particles.
The zeta potential measurement is fairly easy; pipette the sample into a standard cuvette, insert the dip cell that creates an electric field in the sample and an automated sequence measures the induced particle motion either by frequency shift or phase analysis (PALS).