We have a Beckman Coulter Delsa Nano C that provides zeta potential of membranes. But the software get us 2 different values: Zeta potential and Surface Zeta Potential (only when we are measuring membrane zeta potential).
What's the difference between those?
Assume that you have dispersed your nanoparticles in a medium containing some ions (usually distilled and double distilled water has ions). If you take a single nanoparticle into account, it's surface has a charge which is nothing but "surface zeta potential (surface charge)". Assume that the nanoparticle surface is negatively charged. Hence you get a "surface zeta potential" with some negative value. Now as this nanoparticle is present in a solution containing ions, its's surface (negatively charged nanoparticle surface) attracts positive charged ions and these positively charged ions further attracts negatively charged ions and finally it forms a strongly bound inner "stern layer" and weakly bound outer layer (together it's called electric double layer). There will be a potential that exists at the boundary of this surface (it may also be assumed a difference between the potential of the outer layer and potential of the medium). This potential is called "Zeta potential". So, if we are dispersing the nanoparticles in deionized water, the surface zeta potential and the zeta potential should be same.
Please correct me if i am wrong.
Actually, other than monovalent salts such a NaCl, an analytical solution for these potentials is not possible. Another problem is that the surface energy leadds to dissociation of water leading to a corresponding change in pH. If one wishes to perturbthe surface potential least the quarternary ammonium based buffers or any of the Good buffers below 3 mM abolish the pH influence without significantly affecting the surface potential. All these have to be by trial and error.
It seems that in your case 'surface zeta potential' and 'zeta potential' are the same thing. Surface zeta potential refers to surfaces such as a membrane, zeta potential is the general name for the definition of the charge of any substance. However, when determining the zeta potential of particles in suspension (by direct relation to the electrophoretic mobility) this is also called 'zeta potential'.
The calculation of the zeta potential for surfaces and particles uses slightly different equations.
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