I have a sample (Gadolinium compound) which contains nanoparticles of 50nm to 5000 nm (based on observation in SEM) in sizes. I have tried DLS measurement but the results are not accurate. I would like to have a fairly accurate size distribution profile of the sample I have. Any helpful suggestions are highly appreciated.
1.Nanoparticles you collect in conglomerates. Therefore, try to dilute the suspension and again determine with DLS and SEM.
2. If it does not work, then improve or worsen the stabilization of particles with electrolytes or organics. To do this, you need to know the structure of the particles and the dispersant.
Best regards.
This size distribution is large and laser diffraction is more appropriate.
In addition to chemical dispersion, consider using ultrasound to break up agglomerates in your dilute solution before the DLS measurement. The DLS measurement will not be accurate unless your particles are properly dispersed. SEM may not be too accurate as it is difficult to distinguish between agglomerates and aggregates if the particles are not dispersed and completely dispersing them would probably limit the number of particles in the field of view making it difficult to accurately capture the size distribution. You may want to consider a combination of DLS and laser diffraction for small and large sizes, respectively.
@ James You are correct in that some form of dispersion my need to be employed. By conventional understanding, agglomerates are loose and can be disrupted by sonication; aggregates are strong and cannot be disrupted in this manner. A powder is a fused collection of sub- and post micron aggregates and agglomerates and thus the large material (> 1 or 2 microns; density dependent of course) will still sediment in a DLS experiment. See for example:
Nov 11th, 2008. Dispersion and nanotechnology http://tinyurl.com/hpywsge
A modern laser diffraction instrument can cope with the range stated (e.g. Mastersizer 3000 has a stated range of 0.01 - 3500 um or 10 nm to 3500000 nm) so no further technique is needed. If the sample was already in wet dispersed colloidal form and < 100 nm then DLS would be the only choice. At > 100 nm and certainly > 1000 nm then laser diffraction is preferred.
I agree that a combination of DLS and light scattering is particularly valuable especially when the objective is to produce truly nanomaterial (< 100 nm by ISO and ASTM definitions).
Hello Shivakumar, feel free to share the DLS results here. If the distribution does go out to 5 microns then it may indeed not be the best technique for your sample. The size quality report should provide some recommendations concerning the raw correlation function data.
http://www.materials-talks.com/blog/2014/07/10/faq-peak-size-or-z-average-size-which-one-to-pick-in-dls/
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