Mostafa F. Al-Hakkani

Polydispersity index and pH are dimensionless quantities. Zeta potential is measured in volts. Therefore, there can be no mathematical connection between them.

First, I'd like to thank you for your interest, Prof. Yuri Mirgorod. We studied that the pH value results from mV, where each pH unit corresponds to about 57 mV on the pH meter scale. So, I asked about the mathematical relationship between zeta potential (mV) and the pH.

Mostafa F. Al-Hakkani

It is correct to formulate “for some dispersed systems, the value of zeta potential depends differently on pH.” There are disperse systems that do not depend on the pH of the dispersion medium.

Mostafa F. Al-Hakkani Do you mean zeta potential? You say "where each pH unit corresponds to about 57 mV on the pH meter scale". Are you trying to relate the 57 mV measured by the pH meter with the zeta potential reported by, for example, electrophoretic light scattering?

There will be no relationship.

You also ask about the zeta potential at the point of zero charge - that will (nearly always) be 0mV (or close).

For PDI, if you have a charge-stabilized system and it is near/at PZC, it will likely aggregate and you will get a higher PDI than at a different pH where there is significant charge present.

I suspect you are trying to compare two physically unrelated properties just because the way they are measured both involve mV.

I would like to thank you for your interest in answering my question, Prof. John Francis Miller.

Of course, I didn't mean normal pH, just as an example.