If I have a sample of 1 mL containing nanoparticles, and the graph (of volume distribution) identifies two peaks:
100 nm at 70%
200 nm at 30%
Does that mean that 100 nm particles occupy 70% of the sample volume (i.e. 700 uL) and 200 nm particles occupy 30% of the sample volume (so 300 uL)?
In this case we're assuming that the solution is polydispersed with some particles having a size of 100 nm and others 200 nm.
I would also be grateful if you could share any resources on the topic.
Actually there's a very good explanation about what the different distributions mean in the old zetasizer manual from 2004 (PDF attached, page 199). In summary, the volume distribution shows you relative percentages of total particle volume, under the assumption that your particles are spherical. It doesn't relate to sample volume.
Hi Hamed,
The difference between different distribution results is also discussed here:
https://www.materials-talks.com/blog/2017/01/23/intensity-volume-number-which-size-is-correct/
There are different schools of thought on which representation to use, for example volume weighted shows a more representative population of the particles present where as intensity weighted may show a higher contribution from a few large particles.
The intensity weighted result may be favoured as it is a direct result where as volume and number weighted distributions rely on transformations of the data and knowledge of the optical properties of the particles.
Hamed Al-Busaidi In addition to Alex's excellent answer, we have to remember that a volume distribution in DLS has been derived from the original intensity distribution. This mathematical transformation has a bunch of assumptions not least that the optical properties of the material as well as the continuous phase need to be known. For reasonably narrow or bimodal distributions, the conversion to volume is probably fine. The conversion to number is 'deprecated' in the international standards (ISO22412:2017 & ASTM E2490-09(15)).
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