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The gain to control the stability of disperse systems is crucial in determining the performance of the final product.
By measuring the fundamental parameters which affect stability - such as zetapotential, particle size, pH and conductivity investigators can identify, measure and vary the parameters that determine stability.
Zetapotential is the parameter that determines the electrical interaction between particles. A high value, positive or negative, prevents flocculation.
This Zetapotential is measured by applying an electric field across the dispersion. Particles within the dispersion with a zeta potential will migrate toward the electrode of opposite charge with a velocity proportional to the magnitude of the zeta potential. This velocity is measured using the technique of laser Doppler anemometry or also called Laser Doppler electrophoresis. The frequency shift or phase shift of an incident laser beam caused by these moving particles is measured as the particle mobility, and this mobility is converted to the zeta potential by inputting the dispersant viscosity, and the application of the Smoluchowski or Huckel theories. These theories are approximations useful for most applications. More recent models are available which can give a more exact conversion, but require more knowledge of the chemistry of the dispersion.
