I want to measure the zeta potential of spherical particles (d=30µm) with different surface modification. Unfortunately, the particles precipitate during measurement. Can I increase the viscosity of the fluid, e.g. by adding glycerin, to slow down the precipitation and enable reliable measurements? What other work-arounds are possible?
Note: I am not aiming for absolute values of zeta potential but rather would like to compare differently modified particles with each other and obtain a relative statement.
Thomas Hendel
Measurement of the mobility (rather than ZP) will be beneficial. Generally speaking the application of an electrical field will reduce the sedimentation (density dependent - you don't say if the particles are even inorganic or organic. I can think of both glass beads and polystyrene latex that would meet your criteria) tendency as the particles oscillate in the AC field. Alternatively you can allow sedimentation to take place and measure particles in the supernatant. As long as these (smaller) supernatant particles are of the same chemistry as the bulk then the mobility should reflect this - at least you should be able to 'compare and contrast'. Given the size (and density?) of your particles then any ZP measurement wouldn't be a 'sign of stability' anyway.
Thank you Alan for your answer. I can add to this topic that these are organic particles with a density of approx. 1.3 g/cm3.
Thomas Hendel Of course streaming potential is another technique and this is applicable to settling particles and related to charge on the particles in the system. What equipment do you propose to use?
Measure the sedimentation potential!
https://en.wikipedia.org/wiki/Sedimentation_potential
You can easily build your own - much easier than light scattering and ideal for large, sedimenting particles.
If you have access to a Zetasizer, you may just try to see if you can get data from your sample. It would not hurt the instrument. The specification indicates that up to 100 micron diameter might be possible: https://www.malvernpanalytical.com/en/learn/knowledge-center/technical-notes/TN110708ZetasizerNanoZ-ZS-ZS90MaxSize.html
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