To measure the zeta potential of hydrogel membranes and beads, prepare a dilute suspension and use a zeta potential analyzer. For refractive index and absorbance, use an Abbe refractometer and a UV-Vis spectrophotometer on a suitable hydrogel sample or solution.

Zenab Helal

Zeta potential is a characteristic parameter of liquid dispersed systems: suspensions, emulsions, hydrogels.

You have a solid material.You can disperse your material into a suspension, but this will no longer be a membrane, but a dispersed system. If you use it as an electrode relative to a hydrogen electrode, then you can measure the standard electrode potential.

Zeta potential is inferred from movement/ mobility data and is not measured directly. As such, the optical properties are not needed for the particle - only for the continuous phase which is probably close to water. If in doubt, use an Abbe. You’ll find plenty of information on the topic if you conduct a search on ResearchGate. You talk of membrane and beads. What are you measuring?

You can use a Electrokinetic Potential Analyzer (SurPASS 3) to measure the zeta potential on solid hydrogel membranes. An electrolyte solution like 0.001 M KCl is flowed over the surface at a given pressure gradient to monitor changes in voltage across the same. If the surface is charged, the K and Cl ions in the electrolyte will be attracted to it to create a double layer. By applying different pressures the ions get pushed on the surface by shear forces that will induce a change in voltage across the sample. Using a Poiseuille flow model, you can estimate the zeta potential of the solid surface of your hydrogel. You can load solid membranes or hydrogel beads with slightly different flow properties to get a reasonable estimate of zeta potential.

https://www.anton-paar.com/us-en/products/details/surpass-3/