Hello Everyone, I have found that the zeta potential values of my samples are very close to zero. I have used TWEEN 80 and SPAN 80 at different proportion. The HLB value I have kept in the range 5-6. The samples are still stable and I don't see any sedimentation in the samples even after 45 days. Can I call it stable emulsion? If yes, then what will be the use of zeta values (normally literature suggests that the zeta value should be beyond +- 30mV for stable emulsions)?
What reference should i take while measuring the ZP of water-in-oil surface in Zetasizer ZSP (ZEN5600)?
@ Dipankar, I think in your case it is better to measure the electrical conductivity of the emulsion. If there is no conductivity, it's an water in oil stable emulsion.
J. C. Tarafdar Thanks for your reply. I will consider your suggestion.
Zeta potential is a measure of the magnitude of the electrostatic or charge repulsion/attraction between particles and is one of the fundamental parameters known to affect stability.
In the case of an emulsion, its stability can be conditioned by an emulsifying agent or particles and it is around this layer that the zeta potential is determined, with the particularity, in my opinion, that if the layer is made up of both, there must be dependence on the effect of each.
Forget the nonsense you have read about 30mV meaning stable etc. This has to be one of the most confusing and incorrect lies to have entered disciplines outside of mainstream colloid science and has created no end of heartache and wastes of time for many people.
That number came from studies of red blood cells decades ago.
Are emulsions red blood cells? No.
Do you have ANY reason to believe a liquid droplet stabilized by a surfactant layer should remotely behave like a red blood cell? No.
Read a book or papers on what zeta potential is and is not. When you do that, you will realize that there is no right answer to your question.
The literature that claims +30mV (why not -30mV????) is needed for stable emulsions is WRONG.
You also need to understand WHAT your Zetasizer actually measures and how it ESTIMATES what it correctly calls APPARENT (i.e., not necessarily TRUE) zeta potential.
John Francis Miller
Thanks Sir for sharing your knowledge and experience in this field. Your comments are really enlightening for me. I have limited knowledge in this field and when i have gone through the relevant literatures, i was confused to draw a conclusion based on the results i have obtained. I was strictly following plus/minus 30 mV range for the stability as enormous literatures have reported that. However, my results were close to zero. Anyway thanks sir.
Should i go for visual inspection or use of centrifuge to find out Emulsion Stability (ES) and Emulsion Activity (EA)??
Anthony Hutin
Thanks for your reply. I have found the droplet size which is nano-range (60-150nm). But, I am focusing on sedimentation rate to determine the stability. However, even after 2 months, all my samples have not shown any sedimentation or separation. Can you suggest me anything?
I do not recommend zeta potential measurement of an emulsion with oil as the continuous phase in the first place. EDL is very thin in oil and if you ever want to relate zeta potential value to stability in an emulsion, you would be committing an obsolete action. Recently I carried out several zeta potential measurements with clay and also observed the flocculation tendency of the particles via other means. There is NO significant correlation between zeta potential and colloidal stability, this also applies to dispersions such as emulsions.
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