It is generally accepted that for a zeta value greater than 30mV or less than -30mV then the particles will tend to be stable.What is so special about 30mV? Can anybody suggest any reference for the same?
Colloidal Stability in Electrolyte solutions depend not only on ZETA potential, but on the extension of the Electric Double Layers as well. For example, in 1/1 valance electrolyte, ZETA potential at 30 mv is sufficient for Colloidal Stability in 0.01 Mole/Liter electrolyte. The same Colloid at 30 mv Zeta Potential is unstable in 0.1 Mole/Liter of the same electrolyte solution. Double layers are not extended enough for electrostatic disjoining pressure to compensate the forces of molecular attraction between the particles.
Hi Manila,
There is no particular reason to fix a limit to stability for a given value of zeta potential. It has been maybe define like this by the person that are selling zetameter as an apparatus measuring the stability. This is not the case, the colloidal stability is also dependent of the particle size, the ionic strength, the Hamaker constant.
Colloidal Stability in Electrolyte solutions depend not only on ZETA potential, but on the extension of the Electric Double Layers as well. For example, in 1/1 valance electrolyte, ZETA potential at 30 mv is sufficient for Colloidal Stability in 0.01 Mole/Liter electrolyte. The same Colloid at 30 mv Zeta Potential is unstable in 0.1 Mole/Liter of the same electrolyte solution. Double layers are not extended enough for electrostatic disjoining pressure to compensate the forces of molecular attraction between the particles.
Agree with the above answers. '30' should be a hypothetical value suggested by someone for a particular system. Stability will strongly depend on particle size and concentration (especially in case of suspensions) as well. In my experience, hydroxyapatite suspension in ethanol showing ~40 mV was stable for 24 hrs but the larger particles were still sedimented during this period.
Please share, where you found/heard this threshold value!
There is nothing special about either + or - 30 mV in regards to stability. Those values are just guides. I have studied very stable, anionically-dispersed systems with zeta potentials > -20 mV. I believe that a good reference for these values is given in R. J. Hunter's book "Zeta potential in Colloid Science: Principles and Applications."
You're absolutely correct Richard, However me too have read the same book, still I had this doubt.
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