Hi,
I am trying to observe the zeta potential of Laponite RD, by BYK, by changing the pH using auto titration. I mixed 100uL of 0.25 wt.% laponite suspension with 4 mL pure water. The initial pH was 9, and the measured zeta potential was -45 mV, which should be about -20 mV based on the other articles. The trend of zeta-pH was similar to other's results. However, the zeta potential is more negative in comparison with other's results. For example, the zeta potential at pH=3 should be about -6 mV, but I got -30 mV.
I have calibrated the pH meter, and I have used HCl 0.1M to adjust the pH. Is there anything you can suggest to me to do to find the problem?
Thank you.
Hi Gelareh Rezvan , you have diluted the Laponite RD in pure water. If the other results you refer to were diluted in a buffer, then this could be a potential reason for the different result. Zeta potential is a system property, and will depend on all components in the sample, pH, additives, ions. An easy check could be to compare the conductivity of the samples whether they are the same as those in the other data. You may find these two blogs of interest:
https://www.materials-talks.com/blog/2018/03/06/zeta-potential-in-salt-solution-or-any-other-ions/
https://www.materials-talks.com/blog/2018/10/03/debye-screening-how-it-affects-zeta-potential/
Hi, i've never specifically measured the zeta potential of this material, but I do have some suggestions. The salt/ion concentration of your solution can make a huge difference in the zeta potential that you are obtaining. Is the paper you're comparing to in a buffer like Ulf Nobbmann said? are you at a different temperature? To me, the ion concentration is really what is probably messing you up. Try adding a bit of buffer solution, or trying to make your solution with deionized water instead of ultrapure water, or in a dilute buffer. you'll see it will vary a lot. I hope this helps!
Gelareh Rezvan
The pH meter is calibrated against buffer solutions with specific pH, not solution HCl. Therefore, you need to properly calibrate your pH meter. Laponite RD is hydrolyzed. The slightest changes in the composition will be reflected in the value of the zeta potential. If you measure the zeta potential from different batches of Laponite RD, it will be different. Believe your measurements.
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