Hi,
I need to find the correct media to make my positive charge NPs stable in an aqueous media. I have tried different solutions at different pH but the zeta potential does not increase more than 10 mV.
Thank you for your time
Have you demonstrated that 10mV is insufficient or are you assuming that because the measured zeta potential is 10mV then the colloid will not be stable?
The "rule of thumb" about zeta potentials and stability should be retired. It is misleading and colloidal systems today often have much smaller particles than a few decades ago. Wise people quickly learn that the rule of thumb works only some of the time.
It might be better to use a suitable stabilizing /coating functionalization on the nanoparticle surface (?)
Yaride perez pacheco
You do not describe your 'nanoparticles' in any way or how you are determining zeta potential (which cannot be measured directly - only inferred). We do not know the composition and this is vital in understanding modes to stabilization. As I guess you know there are 2 routes (steric and charge - IMHO, poorly called 'electrostatic' - stabilization) and Rebeca Fortes Martín indicates the possibility of steric stabilization above. In this case, with a protective polymer (e.g 50 kDa PEG or PEI) over the particle, then zeta potentials of 0 mV can be perfectly stable. In the case of charge stabilization (which you are hinting at in your question) then typically lower (more acidic) pH's favor more positive charge) and higher (more basic) pH's favor more negative charge. However, the chemistry is vital and high positive charges are found far less often than high negative charges.
Back to the chemistry - while low pH's may favor more positive ZP's then they also favor reaction and dissolution. At higher pH's precipitation of hydroxides can occur or amphoteric oxides can dissolve too.
It's more usual to be able to obtain charge stabilization with negative charge e.g. with oxides the optimum amount of phosphate (e.g. Calgon; sodium hexametaphosphate) is one common stabilization route.
Take a look at this webinar (registration needed) and come back and describe your system in more detail):
Dispersion and nanotechnology
https://www.malvernpanalytical.com/en/learn/events-and-training/webinars/W190528DispNanoMat
DO you know the IEP of the Nanoparticles? for example the IEP of alumina is at pH 8.6. So the zeta potential of the alumina is going to positive below that pH. Above that pH, it's going to be negative.
Another phenomenon thing you can try is to add a cationic stabilizer (assuming the NPs have negative zeta potential) such as PADAMAc (polymer) to stabilize the particles and increase the zeta potential. However, adding a stabilizer like that could lead to particle aggregation due to bridging between the polymer chains on the surface of the NPs. which is known as "bridging fluctuation".
Have you demonstrated that 10mV is insufficient or are you assuming that because the measured zeta potential is 10mV then the colloid will not be stable?
The "rule of thumb" about zeta potentials and stability should be retired. It is misleading and colloidal systems today often have much smaller particles than a few decades ago. Wise people quickly learn that the rule of thumb works only some of the time.
Yaride perez pacheco
It's nearly 2 weeks since you posted your question and no response from you. I trust you are well and have not met any misfortune.
The comments of John Francis Miller are spot on and can be expanded by reading through this pregunta.
https://www.researchgate.net/post/How_do_I_interpret_zeta_potential_values
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