Hello Syam,

Can you confirm what dispersant you are using for your zeta potential measurements? The pH of your dispersant will have a significant effect on the zeta potential of the silica, as shown in the following application note on the Malvern website. This describes the measurement of the surface zeta potential of silica using a Zetasizer Nano and surface zeta plate cell, and shows the results of titrations of surface zeta potential of silica against the pH of the dispersant.

Hope this helps.

http://www.malvern.com/en/support/resource-center/application-notes/AN120914MeasSurfZPSilica.aspx

Should we assume that measurements on Malvern standard latex dispersions produces correct results, that is your system otherwise functions well? How large are your particles? Do they produce a stable enough dispersion?

Hi Stephen Ball

Thanks for the reply.....i tried all the reactions in water medium .....my particles size is about 250-300 nm. even i tried by adding 10 mM NaCl aqueous solution as a dispersant medium to stabilize the silica particles.

hi Roman Kubrin ,

My particle size is about 250-300 nm. i hope they make a stable dispersion. if it doesn't make a stable dispersion, how i come to know that? please give a some idea...

Thank you

If you shake or stir the bottle/beaker with the suspension, how long does it take for the particles to settle down on the bottom? if they settle down much faster than their theoretical terminal speed, then you deal with agglomeration, which means that you zeta-potential maybe indeed close to zero. This is, of course, very strange for silica and provides a hint to heavy contamination of the sample. By the way, i don't get how NaCl can help to disperse the particles, you rather should try to clean your suspension from any salts.

Try measuring standards or at least run a measurement with pure water - if it gives the same result as with you particles, than your measurement cell is contaminated and you are not measuring the zetapotential but simply monitor the dirt or air bubbles.

Thank you so much for yours valuable information Roman Kubrin sir.........

Hi all,

If I understand rightly, purpose of the addition of NaCl is not for stabilization of Silica particles. The main purpose of it is that :

if you use deionized water, the conductivity of the suspension will very low. As a result the signal when apply a voltage is very weak. That lead to risk of high error. That why some measurement with deionized water, we should add some electrolyte (NaCl, KCl,...) to increase conductivity of the suspension.

But take care, if we add too much NaCl, it will effect to zeta potential of your particles. (But with my experiences, 10mM NaCl is ok, it will not affect to the real zeta potential of your particles)

Thank you T.P. Vu sir for your kind information.

Hi

First you can try to make the measurements in buffer solution (I usually used TRIS). Second, avoid the air bubbles - I had this problem with my first measurements, when the air appear between the electrode and liquid (for the negatively charged particles I had got positive charge).

All the best