I read a lot regarding well dispersed particle in suspension have +/-30 mV. I also read positive zeta potential mean particle has positive charge. So, if a cation group show - 30mV, what does it mean? Mean cation group has negative charge? I'm confused.
Please provide more information.
What are the cationic groups? (amino?)
What pH?
Any other components (surfactants etc)?
John Francis Miller Thanks for your concern . I have a nano powder mixing from Ba0.5Sr0.5Co0.8Fe0.2O3 Ce0.8Sm0.2O1.9 ,NaCO3 and LiCO3 by milling method. I run zeta potential on my powder by pH 2 to pH 11( ethanol medium, no surfactant added, pH is adjusted by HNO3 and NH4OH and PDADMAC as dispersing agent)
All of pH showing positive zeta potential and shape of the graph is like mountain in peak at pH 8 ( 30mV). I read a lot that generally acid medium give positive zeta potential and base medium give negative zeta potential. I wonder how is the interpretation of my result .
Most likely the PDADMAC is adsorbing onto your particles (which is the usually dispersing mechanism). PDADMAC has a quaternium ammonium chloride monomer unit which can ionize to give free chloride ions and a positively-charged polymer chain. If your particles do have the polymer on it then the zeta potential will be positive. How this may change with pH depends on the polymer itself.
I'm confused by the ethanol medium. Is that 100% ethanol or an aqueous mix? pH is meaningless unless your acid/base is present. Even then, it would mean very much.
The 30mV = stable rule should only be applied in aqueous dispersions with low levels of salt and without a polymer dispersant.
There are other factors, too, that would require a lot of explanation. Overall, the +ve zeta potential doesn't surprise me.
John Francis Miller yes sir, i am using full organic (ethanol) for my suspension. Im doing zeta potential from pH 2 to pH 11 to know which pH medium give better particle dispersion stability. It comes out pH 8 is the best value with 28mV exactly. Other pH medium give all lower positive zeta potential. Then, i would do electrophoretic deposition coating by pH 8 stablest suspension. Nonetheless, may i know....
(1) What does positive zeta mean to my powder ? Is it showing my powder is positive charge ? and what does negative zeta potential mean ? For example i do see a paper reporting zeta potential on ZnO ( ethanol + deionised water medium, PDADMAC as dispersing agent) It has +37mv and -37mV at pH 5 and pH 9 respectively. What does -37 mV mean ? showing negative charge particle or any explanation ?
(2) based on sir opinion, is it my result showing good trend ? as all pH 2 to pH 11 show all positive zeta potential
Thanks
Zeta potential is only meaningful for a particle surrounded by a liquid that has ions.
The paper you mention is ethanol + water.
How exactly are you adjusting the "pH" with the acid and base? Can you give the final composition of the liquid at pH 2 and pH 11. i.e., how much of the acid and base are you adding to the ethanol? How do you confirm the "pH"? A normal pH electrode? The traditional way of measuring pH doesn't apply to non-aqueous liquids. Technically, pure ethanol does have a pH (i.e., it does dissociate very weakly to form H+ ions) but measuring that is a challenge.
John Francis Miller Ooh ...my suspension ( powder + ethanol +2 ml of pdadmac) originally pH 10. Then, i tuned the pH by adding HNO3 drop by drop into suspension using glass pipette until pH 2 to pH 9 was obtained. Overall, to get pH 2 was just approximately 1 ml of HNO3. The pH value was measured by pH BenchtoppH meter. In my testing, pH 8 give the highest zeta potential.
" 2 ml of pdadmac " - is that solution? What is the solvent?
Regarding the pH meter - it is really just a voltmeter. Inside the electrode is aqueous solution (what it is can vary). When you put the electrode in a liquid, a voltage is developed that depends on the difference in H+ concentration outside the electrode. The voltage has to be converted to a pH which is why the meter has to be calibrated with known pH solutions. The reading you get is only valid for samples with the same solvent composition as the calibration. Even changing the salt concentration in a sample will change the pH response (not by much).
Immersing the electrode in ethanol will generate a voltage but there's no way to convert that to a meaningful pH if the meter was calibrated with aqueous buffers. You would need to generate H+ in ethanol (maybe with ethanoic acid?) and know the pKa for the acid. You could then get some idea.
But you are also adding water to your ethanol (from the acid and base). It may not be much but it could be enough to change the surface charge of your particles.
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