Ankur Verma If you're starting with a powder then it's a laser diffraction experiment, not DLS. You have no free, independent, discrete particles < 100 nm in a powder. For further information, please view this webinar (free registration required):

Dispersion and nanotechnology

https://www.malvernpanalytical.com/en/learn/events-and-training/webinars/W190528DispNanoMat

If water is not working as a dispersion medium even after sonication then try to change the dispersion medium to alcohols(ethanol) etc. But before that, as you have not mentioned sonication time I assume you at least sonicate it for a minimum of 30 min if not increase it to a maximum of an hour. Then go for an alternate dispersion medium. Also, check your water's pH before and after adding your nanoparticles to make sure it's almost near neutral with + or - 1 acceptable(i.e 6,7,8). Also, take your nanoparticle dispersion in low concentration (1mg/100ml) or even lesser concentration.

Hope this helps you a bit

Aravindhan Vanangamudi There is a 'comminution limit'. Sonicating for 30 - 60 minutes with a probe sonicator will contaminate the suspension as the tip disintegrates (if you don't believe me then try sonicating 18 M-Ohm water in such a manner and measuring the conductivity over time). Sonication can also promote aggregation and agglomeration. In organic solvents most of the ultrasound energy is used in boiling the solvent and converting it to vapor. Water is the best medium for transmitting ultrasound energy.

See the first webinar above and this one (registration required):

Ultrasound, cavitation, and the singing kettle

https://www.malvernpanalytical.com/en/learn/events-and-training/webinars/W130619UltrasoundCavitationSingingKettle.html

'I think dry nanotechnology is probably a dead-end' Rudy Rucker Transhumanity Magazine (August 2002)

‘If the particles are agglomerated and sub-micron it may be impossible to adequately disperse the particles……‘The energy barrier to redispersion is greater if the particles have been dried. Therefore the primary particles must remain dispersed in water….’ J H Adair, E. Suvaci, J Sindel, “Surface and Colloid Chemistry” Encyclopedia of materials: Science and Technology pp 8996 - 9006 Elsevier Science Ltd. 2001 ISBN 0-08-0431526

See also:

https://www.researchgate.net/post/How_can_I_overcome_dispersion_issues_faced_while_re-suspending_powder_nanoparticles

Thanks a lot for your valuable suggestions.

I am sonicating water containing nanoparticles for about 20 min at 40 degrees celsius temperature.

And my concentration for nanoparticles was 1mg/ml.

Ankur Verma

‘The energy barrier to redispersion is greater if the particles have been dried. Therefore the primary particles must remain dispersed in water….’

Once your system is dried you cannot easily return to the dispersed state - the same situation as the drained marshes in Iraq. Simply adding water back into the system does not regenerate the habitat... See: https://www.rferl.org/a/1104940.html

Also see:

https://www.researchgate.net/post/Measuring_nanoparticles_by_DLS_what_is_the_meaning_of_sample_too_polydisperse_for_cumulant_analysis

Hi Ankur,

Accurate DLS measurements require that the nanoparticles are well-dispersed in solution to avoid aggregation and obtain reliable results.

In the case of iron oxide nanoparticles, ultrasonication is often used to disperse the particles in solution. However, if ultrasonication is not sufficient to disperse the nanoparticles, you can try the following steps to prepare a sample for DLS measurements:

By following these steps, you should be able to prepare a well-dispersed sample of iron oxide nanoparticles for DLS measurements. It's important to note that the appropriate sample preparation may depend on the specific properties of the nanoparticles and the dispersant used. Therefore, it's recommended to optimize the preparation method for your specific case

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characterization methods are there to characterize a material, not to change a material until it can be measured.

Was talking about bath sonicators Alan F Rawle Yes as you said water is best dispension medium. you are right Titus Sobisch