For DLS analysis, the powder sample should be well dispersed in a suitable solvent with minimum agglomeration. For this purpose dispersants are added. My question is that: Is it necessary to use a dispersant or sometimes the particles may disperse perfectly without adding a dispersant.
Generally speaking if a material is in powder form it is unsuited to DLS and standard laser diffraction is the appropriate technique. This is because a powder (even of small primary size) contains a mixture of sub and post-micron fused fundamental particles. There are no discrete, freely independent, separate particles < 100 nm in a powder. See for example:
Nov 11th, 2008. Dispersion and nanotechnology http://tinyurl.com/hpywsge
November 3rd, 2015 Adhesion and cohesion http://tinyurl.com/zwb2wlh
The only dispersing agent is energy with the key steps in making a stable dispersion of a powder being wetting, separation (often aggressive sonication - basically ultrasound milling), and stabilization. Other additives are in the system to either charge or sterically stabilize the separated particles. See:
January 19th 2011 PST and BDAS - an acronym approach to laser diffraction method development
https://www.brainshark.com/malvern/vu?pi=478888057&text=M021507&r3f1=
Adding dispercent in DSL analysis is dependent on the nature of your particles, i.e. particles solubilty and their charges, if you have charged material in this case you have to run the DLS in presence of electroltyte, KCl is widely used dispercent in this situation, you may need to adjust the pH for water soulabe powder during runing DLS. Before doing so if you get stable particle diameters (since you will get couples of nm readings) over the period of time then you dont have to add any dispercent
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