Up to my understanding, zeta potential is supposed to be the electrokinetic potential at the imaginary surface-of-shear in an EDL. The way it is estimated is by relating it to the measurable electrophoretic mobility/velocity of a colloidal particle upon application of an electric field.
My question is: Can we reliably evaluate particle-surface or Stern-surface potential (or charge) from a knowledge of zeta potential? Better yet, can we use zeta-potential measurements to estimate the location of the Stern or shear planes relative to particle surface?
Assume solid nanoparticles dispersed in water.
No. Zeta potential is, by definition, the electrokinetic potential - i.e., at the shear plane. Take a look at the figure on page 35 of Hunter's Zeta Potential in Colloid Science - first three chapters available for free here:
https://www.elsevier.com/books/zeta-potential-in-colloid-science/hunter/978-0-12-361961-7
In the case where the true surface charge arises from H+ or OH- then potentiometric titration will give you the net charge. There will be a pH at which the net charge is zero (point of zero charge, pzc). If you measure the zeta potential as a function of pH, it will likely cross zero (the isoelectric point, iep). Sometimes the pzc and iep will be at the same pH. Other times, they won't and, from the information, you can infer information such as preferential adsorption of counterions etc.
Combining electrokinetic measurements with potentiometric titration is a powerful combination. And, in the latter case, you get to try your high school titration skills :)
Thank you, Dr. John Francis Miller, for elegantly clearing that up.
And thank you for the great reference which I plan to borrow from the library and study in some detail in the near future.
Dear all, the information you get from Zeta potential may be completed and extended by ellipsometry. My Regards
Dear all, attached is the complete book recommanded by Dr. John Francis Miller. My Regards
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