I am fractionating cotton cellulose into nanocrystals using 3 different organic acids with HCl acting as a catalyst at different concentrations(0wt% ,0.5wt% ,1wt%). I am having to use the zetasizer due to budget constraints to quantify the effectiveness of the fractionations and thus am looking at the size ranges, as well as using the volume/size distribution in conjunction with density to obtain yield. The issue is agglomeration is occurring and particle sizes are nonhomogenous so some samples with much less fractionation are indicating smaller size particles as the larger particles settle quickly and tiny amounts of small particles remaining are measured, whereas the samples with more fractionation have particles suspending in the solution with agglomerates being present. Would you have any suggestions to overcome the problem of trying to obtain a more accurate representation of the actual volume distribution and size ranges? I was considering using a filter to filter out the larger particles however I fear some of the nano particles may be entrapped and thus a non-accurate representation of the nano particle yield will be obtained.
Luke Smit
With settling taking place, then you'll need to use laser diffraction not DLS. You're in the region where the benefits of multi-angular information are present and a distribution by volume can be quantified.
Below 100 nm (the nano region) then the scattering is isotropic (ignoring polarization) and only one detector would be needed for size determination.
Alan F Rawle Thank you for the response, I don't believe I have access to laser diffraction though. I do only need to quantify the yield of nanocellulose, not the larger cotton, so I am thinking of diluting my samples to around 0.02wt% cellulose(I believe nanocellulose should suspend at this concentration in water if I'm not mistaken) and then applying ultrasonication for 5 minutes to encourage the agglomeration to dissociate, after which i can then centrifuge the solution. The larger than nano-sized particles I believe should then settle to the bottom of the centrifuge tubes and I can decant the liquid for analysis and consider the settled particles as non-nanoscale. If I analyse this portion only with the zetasizer I think there may be no settling evident and I could dry and weigh the solid contents of this solution and calculate the nanocellulose yield using the zetasizer results. Do you have any thoughts on this approach?
Luke Smit
You'll have a self-fulfilling experiment if you allow the larger material to settle out - what remains in the top is sub-micron simply because of Stokes' Law. It's a calculation you must do as this will give you a guide as to what will remain is suspension. Removing the large material distorts the distribution. If you consider a single 10 micron particle then it'll need a million one micron particles to make up the same mass (or $ or Rand in terms of value). If you have a 10 micron particle and a 1 micron particle then you can throw away the smaller as it's only 1/1001 of the total mass or value of the system (and it's worse in DLS as it's an intensity or volume-squared dependence). In the 1 and 10 example, then to a number counter the 1 and the 10 are equally weighted and the calculated arithmetic average would be 5.5 units. The volume average would be 9.991. See attached and this webinar (registration required):
Basic Principles of Particle Size Analysis https://www.malvernpanalytical.com/en/learn/events-and-training/webinars/W170216BasicsParticleSize
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