@Loc Truong has sent me a PM as below. In order for the full benefits of the RG experts, I give this PM wider circulation.
Hi Dr. Rawle
I have been following up your answers regarding to Zeta Potential measurement of Malvern Instruments and your suggestions are very informative and educative. Thus I would like to send you this email to get your expert opinion about the measurement of the charged TiO2 particles in tetralin.
The data below show low counts of electrophoretic particles; thus we did not get the sharp peak of ZP measurement. We used Zeta Nano Sizer with dip cell. The particles were encapsulated with double layer of polystyrene/divinylbenzene and polyacrylamide. Reference article confirmed encapsulated TiO2 with charged control agents would have the zeta potential on the surface ~-40mV to -60mV but they used EtOH/ water, not tetralin.
However, our application is used with tetralin and we added charged control agents and surfactant in the formulation with funtionalized TiO2. The particles are able to shuffle with applied bias voltage that proved TiO2 particles have some charge.
I would hope I can get some advice to quantify the ZP of charged particle in low dielectric constant solvents.
Thank you for your consideration.
Best regards, Loc Truong
Hi Loc Truong
I'm the inventor of phase analysis light scattering (PALS) which is the technique that the Zetasizer Nano ZS uses for the more challenging types of samples such as particles dispersed in non-polar media. Indeed, that was the original reason for developing PALS.
You have to consider the electrophoretic mobilities that the instrument is reporting and not the zeta potential. It is the former that is measured and its sensitivity depends very much on the instrument.
Looking at the structure of tetralin, I would assume it has a dielectric constant similar to most hydrocarbons (i.e., 2). PALS measurements with a dip electrode similar to the Zetasizer's require very high voltages. I don't know what voltage was used for your measurements but the reports will tell you.
The attached graph is from my thesis (30 years ago!) which shows mobilities for cross-linked polystyrene latex particles in toluene (as a function of trace water in this case). Note the very small values (x100 less than for most aqueous samples). I used 50V across 2.7mm and 100V across 2.7mm (same results). My thesis is available on my RG page.
Please post the reports from the instrument (including the quality report). I can quickly identify any issues.
Also, "zeta potential" is somewhat meaningless in such media which is why my preference is to report just the electrophoretic mobility.
John.
Thank you Dr. Alan F Rawle for forwarding the question.
Hi Dr. Miller,
I do understand the non-polar solvent would effect on the electrophoretic mobility of particle; thus the mobility input data converted to ZP data would not have good distribution.
I will increase the applied measure voltage in SOP since last SOP I used "automated voltage selection". Report shows ~20-30V.
Thank you
Loc Truong You'll see that John Francis Miller has made some good points. I'll go back even further and ask you why you feel 'zeta potential' measurements will provide any useful information here. There's only one water and the links between stability and zeta potential have been reasonably well explored. In low conductivity liquids (of which there are an infinite amount) then the link between mobility and any derived zeta potential is a tenuous one and subject, in many or most instances, to academic debate. And, like John, I always advise stating mobility in such situations. If you feel that measuring something in such systems will provide you with useful information , then I'd advise you to think again. Size and density are far more important than any charge on the particles (any surface charge fall off rapidly as there are few ions in the continuous phase) and the 'location' of a the slipping plane may be close to impossible. [You state: The particles were encapsulated with double layer of polystyrene/divinylbenzene]. In the case of polymers on surfaces then that slipping plane will lie in the polymer layer and a measured mobility (or calculated zeta potential) of 0 may be seen in perfectly stable systems. Your statement: 'Reference article confirmed encapsulated TiO2 with charged control agents would have the zeta potential on the surface' is erroneous as there is no concept of zeta potential on the surface of a particle. The ZP would be the charge in the slipping plane which lies perilously near the particle surface in such systems and is hard or impossible to define.
So, my major question is what do you hope to achieve in terms of critical quality attributes or product performance predictors by such measurements?
Loc Truong - as well as voltage, try lowering the frequency of the applied field if the software lets you. This increases the amplitude of the oscillation of the particles in the field and so is easier to resolve.
- Badges
- Science topic
- Similar topics
- Chemistry
- Nanotechnology
- Nano