Dear Friends.
I am new user of DLS Test for measuring the size of nano particles i have made by ball milling machine. i am attaching one of picture of my DLS result. plz tell me how to interpret the results from this graph for avg nano particles size.
Hi Vibhu,
There is some misleading information shown earlier.
DLS correlation data can be converted to size information in a number of ways. Z Averages as mentioned earlier is the output of a method called Cumulants, which assumes a single population is present in your sample and as such reports an average size- Z Average. The method does allow for some polydispersity, with a PdI also calculated.
Cumulants and distribution analysis are two separate methods and should be treated separately.
As mentioned, your data shows that you have a sample which is between 200-500nm, but the mode average size is 240nm.
What isn't clear is what type of distribution this is... Is it intensity, number or volume weighted?
If it is intensity weighted is suggests that the sample is relatively stable as there is only a single size population. If it is number of volume weighted, there may be a larger size population present in small quantities which do not appear in this type of data, but may in an intensity weighted plot.
Basic information on DLS data interpretation:
https://cdn.shopify.com/s/files/1/0257/8237/files/nanoComposix_Guidelines_for_DLS_Measurements_and_Analysis.pdf
http://www.horiba.com/fileadmin/uploads/Scientific/Documents/PSA/Webinar_Slides/TR012.pdf
Dear Vibhu sharma ,
Dr. Glodeanu has given two good references to understand the basics of the DLS. As you mentioned since you have prepared the nanoparticles by the ball milling method you might have taken solid precursors and finally got the solid nanoparticles which you have dispersed in a suitable solvent to make your particles disperse. The dispersion medium viscosity is an important factor as it affects the Z average size as in dispersion medium with low viscosity is going to give you larger Z average size of your particles.
The graph shown here gives the z average size of the particle 240 nm. While getting the average size one need to also know whether it is intensity average or volume average or number average particle size. Since larger particle are going to scatter the light more than the smaller size particles as it varies to the power six with the size of the particle and in the report with intensity average size one will get higher Z average size.
Hi,
First check, what is the range of histogram. In figure it is in between 100-1000. Then find average value, here it is between 200-300. The average particle size here is 240 nm.
Hi Vibhu,
There is some misleading information shown earlier.
DLS correlation data can be converted to size information in a number of ways. Z Averages as mentioned earlier is the output of a method called Cumulants, which assumes a single population is present in your sample and as such reports an average size- Z Average. The method does allow for some polydispersity, with a PdI also calculated.
Cumulants and distribution analysis are two separate methods and should be treated separately.
As mentioned, your data shows that you have a sample which is between 200-500nm, but the mode average size is 240nm.
What isn't clear is what type of distribution this is... Is it intensity, number or volume weighted?
If it is intensity weighted is suggests that the sample is relatively stable as there is only a single size population. If it is number of volume weighted, there may be a larger size population present in small quantities which do not appear in this type of data, but may in an intensity weighted plot.
Hello Vibhu,
A good start would be to contact the manufacturer of that instrument for any technical documentation. What appears to be shown is both a distribution (the bar graph) and a cumulative undersize distribution (the line) - and it is probably by intensity. The average size stated below the graph is probably either the peak mean or the peak mode, or it could be the z-average cumulant size. The distribution by intensity, volume, or number can be vastly different for broad distributions, so you should confirm whether it is the intensity or other weighting used in the graph.
http://www.materials-talks.com/blog/2017/01/23/intensity-volume-number-which-size-is-correct/
http://www.materials-talks.com/blog/2014/07/10/faq-peak-size-or-z-average-size-which-one-to-pick-in-dls/
Another point is that at first sight you might think the distribution is quite narrow but it isn't. The size scale of the graph is very wide. 0.1 angstroms to 10 microns! Both limits are way beyond the capabilities of the technique. If the scale was more realistic (10 to 1000nm) then the broadness of the distribution would be more obvious.
- size distribution
- volume distribution
- intensity distribution
- mean size particle
- polydispersity (PdI) values
- typ sample monopolydisper or polydisper
- zeta potentail
Yes, the above "keywords" are good search topics for those getting started with dynamic light scattering DLS.
Concerning distributions: "Which size is right?" http://www.materials-talks.com/blog/2017/01/23/intensity-volume-number-which-size-is-correct/
Concerning mean size: "FAQ mean z-average size" http://www.materials-talks.com/blog/2014/07/10/faq-peak-size-or-z-average-size-which-one-to-pick-in-dls/
Concerning polydispersity: "What is PDI in DLS?" http://www.materials-talks.com/blog/2014/10/23/polydispersity-what-does-it-mean-for-dls-and-chromatography/
Concerning zeta: "what is zeta deviation?" http://www.materials-talks.com/blog/2017/09/05/what-is-the-zeta-deviation/
And a general startup guide to DLS at http://www.materials-talks.com/blog/2015/10/22/new-users-of-dls-the-zetasizer-quick-guide-to-perfection/
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