Measuring Zeta Potential in Organic Solvents using the Univette
The ability to measure the stability of nonpolar dispersions is important to predict their shelf life. This is relevant for a wide range of industries such as paints and coatings, agrochemicals, lubrication technology and the pharmaceutical industry. Zeta potential, a parameter related to the surface charge of the suspended particles, is a useful indicator of dispersion stability.
The surface charge of particles is greatly influenced by the solvent in which the particles are suspended. A key parameter influencing particle charge is the solvent’s relative permittivity, also known as dielectric constant. Permittivity is a material property that influences the Coulomb force between two charged points in the material, and the relative permittivity (also termed dielectric constant) is a factor by which the electric field between the charges is decreased relative to vacuum. If particles are suspended in a solvent with a high relative permittivity, they acquire a surface charge relatively easily. If the solvent exhibits a low to moderate relative permittivity, ionization of the particles is only partially possible. The dielectric constant also provides a rough measure of a solvent’s polarity, with solvents displaying a dielectric constant inferior to 15 considered nonpolar.
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