The zeta potential (ζ–potential) is the potential difference across phase boundaries between solids and liquids. It’s a measure of the electrical charge of particles are that are suspended in liquid. … Zeta potential that is less negative than -15 mV typically represents the beginnings of agglomeration of particles.

Zeta potential is defined as the potential difference between the dispersion medium and the stationary layer of fluid attached to the particle and it is measured by a zeta potential analyzer.