Zeta potential, in Colloid Chemistry, refers to the electrostatic potential generated by the accumulation of ions at the surface of the colloidal particle which is organized into an electrical double-layer consisting of the Stern layer and the diffuse layer. The zeta potential of a particle can be calculated if the electrophoretic mobility of the sample is known by Henry's Equation:

$U\_e=\backslash frac\{2\; \backslash varepsilon\; \backslash zeta\; f(ka)\}\{3\; \backslash eta\; \}$

Where $U\_e$ is the electrophoretic mobility, $\backslash varepsilon$ is the dielectric constant of the sample, $\backslash zeta$ is the zeta potential, $f(ka)$ is Henry's Function (most often used are the Huckel and Smoluchowski approximations of 1 and 1.5, respectively), and η is the viscosity of the solvent.

The zeta potential of a sample of colloidal particles is easily quantified using an LDV, or Laser Doppler Velocimeter. The LDV applies an electrical field of known strength across the sample, through which a laser is then passed. The electrophoretic mobility of the colloid will dictate the velocity with which the charged particles move which will then induce a frequency shift in the incident laser beam. Using either the Huckel or Smoluchowski approximation for Henry's Function, the dielectric constant of the sample, the viscosity of the solvent, and finally the measured electrophoretic mobility, the zeta potential of the particles within the colloid can be calculated.

The primary relevance of the zeta potential of a colloid is as a relative measure of the stability of that system. The DLVO theory for colloidal interactions dictates that a colloidal system will remain stable if and only if the Coloumbic repulsion arising from the net charge on the surface of the particles in a colloid is greater than the Van der Waals force between those same particles. When the reverse is true, the colloidal particles will cluster together and from flocculates and aggregates (depending on the strength of the Van der Waals attraction and the presence/absence of Steric effects). Since the higher the absolute zeta potential, the stronger the Coloumbic repulsion between the particles, and therefore the lesser the impact of the Van der Waals force on the colloid.

Steric effects on the stability of nanoparticle-based colloids have been observed with particles coated with proteins (Streptavidin, Bovine Serum Albumin), oligonucleotides, polymers (Polyethylene glycol), and even functionalized hydrocarbon chains (11-mercaptoundecanoic acid).

Other types of particles such as the mature sperm suspended in medium also possesses a zeta potential or electrokinetic potential. The sperm has a negative electric charge which decreases with capacitation characterized by membrane alterations and the influx of calcium ions into the sperm. The zeta potential of the mature sperm has been reported to be due to charged sialoglycoproteins anchored on the sperm membrane, acquired during its transit through the epididymis.

Physical chemistry

Zetapotential | Zetapotensial