I am trying to measure the zeta potential of o-in-w Pickering emulsions stabilized by silica nanoparticles using a Malvern Zeta Sizer with Folded Capillary Zeta Cells (DTS1070). For a bit of context, my research group works with colloidal nanomaterials and we have experience with zeta potential measurements of colloids but not with emulsions. With this in mind I have the following questions and would really appreciate everyone's opinion:
1. Is this even doable with our current setup? Do we need a different type of cell or an add on to the instrument?
2. Are there anything to look out for in regards to making the sample? For example, is there a certain size limit to the emulsions before they get too large to be suitable for zeta potential analysis? What should the concentration of the emulsions in the solution be like?
Thanks
Yikai Xu Measurement of mobility should be relatively simple. You could use the dip cell, but the capillary cell should be fine. Major issue with emulsions is (any) dilution which should be in the 'mother liquor' - the same ionic, surfactant, and stabilizer content as the starting material. You can recover this by centrifugation, filtration or knowledge of the chemical make-up. Conversion/interpretation of mobility to zeta is another question... The surface of your particles is heterogeneous and the components will influence the potential in the slipping plane in a (probably) hard-to-predict manner...
If the sample is sedimenting or creaming it could be unsuited for measurement. Mobility of larger particles will be smaller anyway.
you should ask about the goal of the measurement. Pickering emulsions are definitely emulsions with strong steric stabilization, so zeta potential seems to be a less meaningful parameter for stability characterization.
The capillary cell should be okay but I strongly urge you to make measurements at a series of applied voltages. My tests repeatedly show that the measured mobility is voltage-dependent with all the samples I have tested on my Zetasizer Nano. It also varies according to whether the so-called monomodal mode (i.e., PALS) is used or the general purpose mode (which is a peculiar hybrid that operates not in the way the manufacturer would have you believe). I have observed up to 30% variation in results from a given sample just by changing the measurement configuration of the instrument.
If you want to do more robust measurements, invest in a dip cell. The folded cells are fine for quality control applications but have serious limitations (that you won't read about).
Hi All, thanks for your suggestions. I found them quite useful. Apologies for not writing sooner. This was originally something suggested by a peer reviewer for one of our up coming papers. In the end I decided to not do zeta measurements since our Pickering emulsion droplets were a few millimeters in diameters and clearly couldn't be driven to move by applied potential. This was also why I was a bit baffled by the suggestion in the first place which led to this question.
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