Hi
Which technique is reliable for measuring the surface charge (or zeta potential) of particles which settle down in a solution Or particle size bigger than 20 um which is the upper range for most of Zetasizers.
Hi SIna,
Surface charge and zeta potential are two different things. Surface charge is the density of charges on the particle surface, whereas zeta potential is the potential at the shear plane of a particle during electrophoresis. Zeta potential therefore gives a practical value that can help understand stability, but it says nothing about the charge density of your system. For charge density I would recommend using a streaming potential titrator, e.g. Mütek PCD05 from BTG or similar. These measure streaming potential as a function of either pH or the quantity of an oppositely charged polyelectrolyte to neutralize the surface charge. When pH is monitored (titration with acid or base) on a streaming potential analyzer, one can derive the point of zero-charge. There is a lot of paper and pulp industry I guess in Norway and these people nearly all use Mütek instruments meaning you should have no trouble finding an instrument somewhere.
Last advice, when determining particle charge, be sure to accurately fix solution pH as it may have a strong effect (if there are weak acidic or basic groups) on particle charge.
I hope this helps!
Kind regards, Leo
One question that springs to my mind is what are your reasons for measuring zeta potential for large particles? Inertial forces overcome any attractive van der Waals forces at these sizes, so this cannot be an attempt to gage stability - indeed the size and the density cause sedimentation, as you've already indicated.
Surface zeta potential is different from colloidal zeta potential which is not the same as surface charge density but can be correlated with it. This company called Malvern has
This company called Malvern has zetasizers which uses laser doppler for measuring zeta potential.
I am attaching some webinars on this topic.
http://www.malvern.com/en/support/events-and-training/webinars/W170124SurfaceZeta.aspx
First I want to say 'Thank you' to: Leo, Ricco, Alan and Abhilash. All answers are helpful.
Just I want to make my question clear:
During precipitation/crystallization, we will get different crystals at different operational condition. I want to measure zeta potential for crystals (or if practically it is not possible go for surface charge).
Zetasizers has a cut-off for size of particles which is around 20 um and crystals are normally bigger than this ...
Just wanted to add that the upper size limit for zeta potential is close to 100 um - the concern is sedimentation. In other words, your issue appears to be that the crystals may be 'dropping out' of the beam. If you could use a dip cell (longer sedimentation path before being lower than the beam), or re-agitate, or change the density you may be able to reduce this effect to such an extent that data can be taken. There is a technical note showing zeta of 97micron polystyrene latex in sucrose water on the Malvern site.
http://www.malvern.com/en/support/resource-center/technical-notes/TN121104ZetasizerPerformance.aspx
Thanks Ulf, you are right. I tried to use high concentration cell too but the results was not consistent. I will try to know more about dip cell too. Now I am wondering how I can keep the particles in solution (not settling down) without any substantial affect on their original properties !??
For the rough estimation you don't need to buy special equipment. Two simple setups:
- column with several vertically aligned electrodes+voltmeter. Record sedimentation rate (optical or balance method) and measure potential differences. So called, sedimentation potential (phenomenon opposite to the streaming potential) is the function of zeta potential;
- vertical parallel plate cell with electrodes installed along the side walls+power supply+microscope/camera. By deviation of particles trajectory from the vertical ones under electric field you can measure electrophoretic mobility :)
There are some theories out there that can accurately cspture surface potential os surface charge. Check PCCP paper on rational design of solid acid cstalyts for cellulose hydrolysis using colloid theory.
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Materials Science
- Materials Chemistry
- Polymer Chemistry