Physical Properties of Dispersions

 

It is important to realize that while dispersions are often judged upon their macroscopic behavior, such as rheology, feel (cosmetics) and cover ability (for paints) their reason always lays in the molecular properties. It is therefore important to be able to characterize both the macroscopic as well as the molecular properties.

Particle surface charge

The charge at particle surfaces can be determined by titration. An indirect method is through the analysis of electrophoretic mobility. This method does not render the surface charge but rather the Z-potential, which is the potential caused by the surface charges, at the slipping plane of a moving particle.

Particle surface chemistry

The surface chemistry of particles can be determined by XPS (see surface analysis) but also by infrared or Raman spectroscopy. An alternative method is through measurement of the wetting properties of the powder or adsorption measurements using gas chromatography.

Turbidity of dispersions

Turbidity measurements are used for determining the change in the dispersion with respect to time, settling or creaming of the system. Using automatic systems the lifetime of emulsions, or dispersions, can be characterized at various temperatures.

Rheological properties of dispersions

The rheological properties of emulsions and suspensions are functions of the molecular properties of the formulated systems. Formulations are designed with respect to their use and their rheological properties. For example a paint should not sputter while being applied with a roller, but it should also be able to level and not give sagging while drying.

Dissolution Test Instrument

The dissolution test instrument is used for monitoring release profiles of target molecules into solution. The instrument is of important use in pharmaceutical formulation where tablet dissolution is a standardized method for measuring the rate of drug release.