During characterization of nanoparticles through measuring the sedimentation rate in DMF the samples give different rates of sedimentation. The inference was theoretically based on the ability of some samples to form large aggregates leading to increasing the particle size and therefore increasing the sedimentation rate. My question is how can I prove this? Which test can I make to prove or deny my assumption?
Elsayed Mostafa Abdel-Hameed
The comment 'During characterization of nanoparticles through measuring the sedimentation rate in DMF' is an oxymoron on 2 counts. Truly nano material will not settle/sediment. Characterization means nothing unless you can relate this to critical quality attributes or product performance indicators. The answer is 42 as posted in your question. See:
https://www.materials-talks.com/blog/2014/02/06/characterization-is-a-number-42-not-a-goal/
First, I assume you've carried out a Stokes' Law calculation. If your particles are truly nano (< 100 nm) then they will not sediment. See ASTM E2490-09(15).Thus they are in the micron plus size, if they are sedimenting.
If you've started with a powder then you'll have a mass of sub- and post-micron aggregates (hard-bound) and agglomerates (soft-bound; separable by sonication).
What is your material and its density? Did it start as a powder? Also see:
- Dispersion and nanotechnology https://tinyurl.com/y2wfzed7
You must need to test your samples using Particle Size Analyzer (PSA) / Dynamic Light Scattering (DLS) method to exactly know the particle/agglomerate size.
Suhaib Umer Ilyas
If the particles are setting then DLS is not appropriate for PSA.
Dear Prof. Alan F Rawle
I agree with you. If the particles are completely settled, then DLS analysis is not appropriate. It may work for freshly prepared samples showing good dispersion at the initial stage (probably after ultrasonication).
John Francis Miller
Agreed. And all I was talking about was to carry out a calculation. Needs no instruments or tests at all...
As you indicate, a simple set of vial tests (e.g. 20 mg in 20 mL of fluid) can be used to measure sediment height which gives indications as to stability of the sol plus the packing (loose or tight) of the sediment will indicate whether high ionic strength has affected the double layer). Note the tightness and looseness of the floc in the attached 'stability' experiments for a polishing agent as the concentration of the ionic additive (phosphate) is changed.
The webinar from which this is extracted talks quite a bit about this slide. Indeed one could spend 42 minutes or 42 seconds on the description.
See:
Dispersion and nanotechnology https://tinyurl.com/y2wfzed7
To further illustrate Alan F Rawle and my comments, this is an example I generated a few days ago in order to determine the critical aggregation concentration (c.a.c.) of CaCl2 required to aggregate a 1.5%vol dispersion of 160nm ZnO. Increasing approx. 1.1mM per cuvette from left (0mM) to right (9mM). It clearly identifies the c.a.c. to be close to 4.5mM. You can see the sediment height of the aggregated samples increase will increase electrolyte concentration, too. I was told this material was sterically stabilized. Never believe what someone tells you!
This experiment took less that 15 minutes from start to finish.
John Francis Miller
Good slide! Illustrates the point well. Ca2+ is also a known destroyer of parenteral soy emulsions. I'd like to see the same slide with Al3+ additions,
Are you saying that I shouldn't believe what you tell me?!
Coincidently, I'm doing AlCl3 today.
I don't necessarily believe what one of me tells one of the others.
John Francis Miller
Sure, skeptical is always a good starting point. How's the Schulze-Hardy rule?
For the system above, 2mM for AlCl3 vs. 4.5mM for CaCl2. Image is after ~15mins standing. Final sediment heights will be interesting (to me).
To use a hideous corporate term, "directionally correct" (i.e., qualitatively as expected).
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