Dear Konrad,

The IUPAC recommendations I mentioned are actually for polymers - please, take a look: Pure Appl. Chem., Vol. 81, No. 2, pp. 351–353, 2009 (doi:10.1351/PAC-REC-08-05-02).

In nanoparticles field, many conventions are still used: dispersity (Chem. Rev. 2004, 104, 293−346; doi:10.1021/cr030698+ - good review that is worth citing!), polydispersity (doi:10.1021/jp5108125), PDI (doi:10.1007/s00396-012-2868-7), or even the mix of polydispersity and PDI (doi:10.1007/s13404-012-0069-2).

In our recent paper, we used the term "dispersity" (doi:10.1134/S0036024416010301).

As I remember, the term "dispersity" is now recommended by IUPAC instead of older "polydispersity" or "polydispersity index". Dispersity is calculated as d=SD/mean, where d - dispersity, SD - standard deviation, mean - arithmetic mean. So if you've got 10+-2 nm o your histogram and 10 nm is mean, and 2 nm is standard deviation, the dispersity is simply d=2/10=0.2

Hi Moritz,

the width of distribution of particle sizes obtained from TEM or SEM could be determined in analogy to the molecular weight distribution of polymers. That means you have to calculate volume average size and number average size (arithmetic mean). Their ratio is then the polydispersity index. This is the way how the distribution of particle sizes is usually described in the field of polymer blends and composites.

Dear Moritz,

Very simple. Do all statistics and get your distribution (Gaussian-like). Make sure that is monomodal, otherwise you should deconvolute.

For the single distribution, calculate the mean value (mu) and the standard deviation (sigma). The polydispersity is the ration sigma/mu.

Good luck!

SALUT!

Tony

Hello all,

Thanks for the answers... I just needed to confirm the standard. Thanks for your answer Andrei. Very interesting on the IUPAC standard. There is just so much variation out there :) sigma sometimes is used for the dispersity itself. Then there is values in percent like 5%, which is sometimes calculated differently from the ratio you stated Antonio (not 0.05)... However, this should be solved, I will keep the way I did it which was sigma over mu as well,

Cheers.

For whatever it's worth, when the breadth of the distribution of particle sizes was a hot topic some time ago, we used the ratio of the weight average to the number average to provide a ratio that we called the poolydispersity.  Thus, a ratio of 1.1 or less was arbitrarily called monodisperse, while various commercial latexes ranged up to as much as 4 on this scale.  At the time, this was important because workers in the field were diligently seeking synthetic means of achieving very narrow distributions, because such distributions had desirable film characteristics relative to broad distribution products.

I simply mention this, because it is a different ratio than mentioned by others in this section.  As with most such topics, there is no correct answer, just a consensus at the moment in time that the question is posed.  It sounds to me like the consensus has shifted over the past 2 decades. 

Sorry F. Louis,

What you mentioned is th epolydospersity index for... polymers! PDI = Mw/Mn.

What Moritz was looking for is polydspersity for collodal particles p = sigma/mu

SALUT!

Tony

I would like to give citations to our upcoming paper and I need good example with  the definition of "dispersity". Do you know any paper that is good to cite?

Dear Konrad,

The IUPAC recommendations I mentioned are actually for polymers - please, take a look: Pure Appl. Chem., Vol. 81, No. 2, pp. 351–353, 2009 (doi:10.1351/PAC-REC-08-05-02).

In nanoparticles field, many conventions are still used: dispersity (Chem. Rev. 2004, 104, 293−346; doi:10.1021/cr030698+ - good review that is worth citing!), polydispersity (doi:10.1021/jp5108125), PDI (doi:10.1007/s00396-012-2868-7), or even the mix of polydispersity and PDI (doi:10.1007/s13404-012-0069-2).

In our recent paper, we used the term "dispersity" (doi:10.1134/S0036024416010301).

Dear Andrei,

Thanks a lot for your accurate answer, it is very useful.

Does anybody have a reference which relates the PDI values with feature of the particles?

For instance...PDI values less than 0.1 are highly monodispersed.

                         PDI values between 0.1 and 0.2 are monodispersed tending to be highly monodispersed.

Something like that!!

Thanks a lot in advance.