I am trying to determine the size of micelles of a surfactant in toluene and THF, but each time the size determined from intensity is showing two peaks, one is below 10 nm (I assume that is my micelles) and the other higher than 100 nm, the report of the quality of data is always showing "data of poor quality, might be presence of sedimentating particles".
I am using a Malvern Zetasizer, and new cuvette, I tried my solutions filtered and non-filtered, I even tried surfactants in water and I prepared the solution about 4 h before analysis, but I still cannot figure out from where I am having that artifact peak with large size which is affecting the determination of the micelles size.
Another question, is it possible to detect micelles with a size around 2 nm.
Thank you
Hi Suomia,
first, check your count rate for spikes and oscillations. Make sure that surfactant solution is not very diluted. If it's not the case and the count rate is a horizontal line without any spikes, then it's possible that you observe some kind of kinetics - micelles life time etc. Try a filter with low porosity - 50 nm or so.
Dear all, this situation is very normal and occurs at first trials if some operating parameters are not well selected. Major aspects to consider are summerized in the attached files. My Regards
This paper can help you
https://www.sciencedirect.com/science/article/pii/S0168365919301130
Hi Soumia Cheddah , it would be helpful to show some actual correlation data, or even attach the dts data file.
In general, it should be possible to measure reverse micelles. Have you tried centrifuging the sample prior to measurement? Filtration may work, however it can occasionally lead to the formation of wormlike micelles (depending on sample type and condition), making the detection more complicated.
Yes, it is possible to detect micelles under 2nm size, for example 1-s-Nonyl-beta-D-thio-glucoside or FOS-choline-10 ( in Chapter Characterization down to Nanometers: Light Scattering from P...
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What sample cells are you using? I assume glass or quartz. Have you checked the surface of the sample cell for small scratches etc or made sure it is thoroughly clean? You may not see them by eye but if you put just toluene in the cell, put it in the instrument and look at the laser beam, you make see unwanted scatter from scratches etc.
Thank you all for your answers.
I will try again the experiment taking into account all your suggestions and then share the new data.
maybe your surfactant is not fully soluble or only very slowly soluble, likely it needs also water to form the reverse micelles.
Please find attached the data of my last trial using Triton-X 100 in water prepared at two concentrations 0.2XCMC and 2XCMC + results of a water blank.
Sample preparation: first I filtered water, then prepared a solution at 10XCMC agitated for few minutes then US for one hour. After that I made the dilutions to get the two concentrations I wanted, agitated for few minutes then US for 30 min, after that I let the solutions settle down for 2 hours before analysis. The cuvette was a new one. Looking forward for your suggestions and comments. Thank you
Is it possible you trap air when you prepare your solutions? Maybe there are some small air bubbles. Whatever it is, it is clearly very large - enough to skew the mean size to be more than 1000nm.
You might only need one such bubble duration a measurement to overwhelm the contribution from the rest of the sample.
John Francis Miller With the naked eyes I can't see any bubbles but since it is a solution of a surfactant, it tends to foam so there might be some invisible bubbles but I am not sure. To check if this is the issue, I am going to try again the experiment but I will transfer the solution to the cuvette before analysis and leave it for some time to get rid of any possible foaming.
what is the wavelength of the laser used in the Malvern Zetasizer used?
If you know that your size distribution is great, then I think this might be due to either evaporation of your solvent gradually with time (so you may try to reduce the measurement time), or the laser used induces some kind of interaction with your material. In both cases, the particles would come together and agglomerate. You may confirm this with TEM images of the solution before and after the DLS measurement.
you may also need to check different concentration of your sample to find the optimum dilution for this particular sample.
I have had the same problem before for niosomes. You need to carefully check your SOP and choose the material with refractive index near to your sample.
you can also try to filtrate the samples thorugh sryinge filters of smaller pore sizes than 0.5 μm
You'll need to filter to 0.02 microns or better to see such small material. Sucrose molecules with a radius of ~ 0. 3 nm have been measured successfully by DLS. Look for a paper by Mike Kaszuba.
Soumia Cheddah
You promised to share your research following expert recommendations. If you have done an experiment with water, then I recommend looking at our article.
Article Structure of Micelles of Sodium Dodecyl Sulphate in Water: a...
Reverse micelles can form dimers, trimers, depending on the solvent, and micelles with solvent, which solvate ionic groups.
Soumia Cheddah
We have not heard from you since July 22nd. I hope you are well and have not met with any accident...
Hi Soumia Cheddah , the data you shared are in a format which looks quite different from any recent Zetasizer (Nano or Advance series) data. The error message could be from a Zetasizer Nano, however the graphs do not resemble that. Is this system older than ~15 years? As far as detecting 2nm micelles: this may be challenging with that setup (90 degree scattering angle?).
and if you do indeed have a Zetasizer Nano, you can find the data dts file as described in https://www.materials-talks.com/blog/2014/08/19/faq-how-can-i-submit-a-data-file-to-the-help-desk/
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