Dear Fangjie,

Just two warnings about comparing zeta potentials of ground versus unground samples.  The native (unground) particle may have a different surface chemistry than the inner portions of the particle.  Upon grinding, you may expose surfaces that don't resemble those on the native unground particle. 

Also you must be cautious that the native unground particle does not have a ZP that is partially the result of chemisorbed or physisorbed species.  These will not be at the same levels on the freshly exposed ground particles and may never be able to reach that concentration.

Best regards,

Mike

Hi Fangjie- the zeta potential is related to size as mentioned above, specifically the relation of Rh to the thickness of the ionic double layer. If Rh >> double layer thickness, than the Smoluchowski equation is used. If the opposite is true where the double layer thickness >> Rh then Huckel's equation is used.

Tanford's classic book explains this in much greater detail: http://www.amazon.com/Physical-Chemistry-Macromolecules-Charles-Tanford/dp/0471844470

Hi Fangjie, The zetapotential is dependent on various factors such as the particle size, the Dispersion medium (solvent type - polar or non polar) and also the viscosity of the dispersion medium. As Smoluchowski equation has all this parameters in use. At the same time i agree with William Sir answer too, where the ionic double layer formation is done and also the debye huckel theory etc. Well the equation also constitute radius of the particle. Since zetapotential denote the stability of the system, in all to have a stable colloidal dispersion you need various factors into consideration.  At the same time various physical parameters, such as added ionic concentration, centrifugation rate, temperature etc would also effect the zetapotential of the system. Hope this answer help you. 

If my answer is felt inappropriate kindly let me know.

Thanks Mahesh 

Also if you are grounding your sample...i agree with Mike bender answer too the surface chemistry of the material may be shifted this will surely affect the zetapotential.

Generally speaking:

• Size and zeta potential are not related - just more surface charge over a larger particle, so the zeta potential remains the same independent of size
• At 150 um (or even 10 um).  zeta potential is unlikely to be relevant to stability - size and density being more important to settling.  This is because inertial effects are much greater than any attractive van de Waals effects.  See:

Adhesion and cohesion

https://www.malvernpanalytical.com/en/learn/events-and-training/webinars/W180725AdhesionCohesion

You don't need to grind your samples for a measure of zeta potential.  Shake with water, allow to settle for a few minutes, and measure the (submicron) supernatant.  I agree - grinding is very likely to alter the charge on the surface as surfaces in air tend to be fully oxidized.

Hello friends, for hydroxyapatiteHAp), zeta potential values were increased with increasing calcination temperature. What can i interpret from this experiment?? Is their any possibility of increasing particle size??

That you have changed the surface of the particle - if you're comparing like with like with respect to external ionic conditions.  With calcination you increase the particle size of the material by aggregation.

We have been testing the effect of particle size on zeta potentials of crushed shale (rock) samples for a couple of years now and I can say that zeta potential does change by particle size at least for shales. However I believe that such changes are originated from the heterogeneity in surface chemistry as above-mentioned.  Having said that, it seems that at least for partially heterogeneous materials, there should be a REV in which the zeta potential will not be influenced by particle size any further that we are working on now!

Hi Fangjie Qi , just a comment. In case you have a Zetasizer, the specification for zeta potential is up to 100 microns, for DLS sizing the upper limit is 10 microns. And you could always experimentally try to see if it is measurable.

There is a recording about zeta potential data quality at https://www.malvernpanalytical.com/en/learn/events-and-training/webinars/W061011ZetaPotentialQualityReportZetasizerNano.html

Is it possible to calculate particle size from zeta potential results?

Ibrahim Elagib You should open another question to avoid confusing this thread and also getting responses pertinent to your specific question.

No - DLS is Brownian motion in the absence of an electrical field. Mobility (from which ZP can be inferred) is constrained movement in an electrical field. Because of the similarities, then typically, the same equipment can be used for ZP and DLS.