Physical and Chemical Methods of Liquid Dispersion

The techniques that are used in the dispersion of powders in both aqueous and non-aqueous media are quite similar. Dispersants aid wetting and stabilization of a suspension can be ionic (anionicor cationic) or non-ionic. However, concentrations of dispersants must be low. Otherwise, their properties are reduced or even inverted (i.e., cause aggregation or flocculation). In dispersing a powder in a non-aqueous medium, it is critical to select an organic solvent that is a good diluent as well as dispersant, although there are many organic dispersant aids. Aqueous surfactants are primarily responsible for reducing surface tension, hence aiding in the dispersion of powders in aqueous systems.

The first task in dispersing a dry powder is the wetting of the sample with diluentor dispersant, if needed. Gentle spatulation of the resulting paste prior to addition of diluent further aids the dispersion process. Once the diluent is added, a sample of the slurry can be placed on a slide for a microscopic evaluation of the effectiveness of dispersion. Providing that the sample is well dispersed, the use of a magnetic stir bar is suggested to keep the sample fully dispersed, so are presentative sample can be drawn for analysis while stirring is in progress.

Physical Methods of Liquid Dispersion

Chemical Methods of Liquid Dispersion

Wetting agents:Used to lower surface tension (e.g., hydrophobicity) between diluent (typically water) and particle (usually non-ionic agent).

Surfactants: “Surface active agents” increase the surface charge of the particles in order to cause them to repel one another so that they remain properly dispersed while in the suspension.Types of surfactants include:

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Stabilization by Surface Charge

Common Ions

Multiple-charged Ions

Surfactant Ions which charge the surface

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