Hi everyone,
I have deacetalyzed low molecular weight chitosan polymer which is soluble in %0.5 (v/v) acetic acid solution. I prepared chitosan/acetic acid solution (0.5 mg/mL) and used DLS to see if there are any nanoparticles in the solution. I saw that there are great number of small nanoparticles (about 60 nm, %99 by number) in solution, however, PDI is about 0.8 which is very poor.
Here is my question: How could a linear polymer chain dissolve and form spheres in solution? And If they are not sphere, what does the 60 nm stand for? Is it particle size or different thing? Unfortunately, I do not have chance to use TEM to see morphology.
Please warn me if I am not clear, I will be clear as much as I can do. Thank you for your answers.
I assume you filtered all your solutions through a 0.02 micron filter?
Alan is right, we did same thing and got size in 2200-3000 nm with zeta potential
+2 mV.........
Dear Mr. Rawle, thank you for your answer. I filtered my solution with 0.22 micron filter to see what is going to happen: Even smaller particles have formed about 5 nm (%99.9 by number). However, great amount of particles are about 2-3 micron present in solution (i mean by intensity).
Dear Mr. Saharan, thank you for your answer. As I said in first paragraph, there are particles about 2-3 micron but small number. But I think your zeta potential is too small, I measured mine and obtained 70 mV which is reasonable for only chitosan chains.
I am still confused and will try other characterization techniques to find out what is inside of the solution.
If zeta potential near about 70 mV then chitosan may have very high biological activity.Any how I may check our zeta result again to verifying.
Dr Alan, in Mr Ugur case, what is the better way to explain chitosan solution, intensity based or by number distribution? After filtering, solution may contain very less of chitosan material?
Vinod - DLS does not measure or count the number of particles in the system. In order to count (nano) particles then you need a system such as NTA or RMM. The recommendations of the ISO (13321:1996 & 22412:2008) and ASTM (E2490-15)standards are that the z-average and polydispersity index plus intensity distribution are the most robust parameters to report for DLS measurements. In the case of a narrow distribution (as would be expected for a single molecule in solution) then the values of the intensity, volume, and number means would be expected to be very close. In a monodisperse situation (impossible to achieve in practice) then they will be, of course, identical.
There will always be huge numbers of particles in any nanosystem. Consider that 1 million 1 nm particles will only equal the mass of a single 100 nm particle. We don't sell or buy systems (your breakfast cereal?) on the number of particles - generally on the mass or volume.
All solutions in DLS must be filtered to the level that you want to measure. For example if you are looking for sub-20 nm particles then all solutions should be filtered better than 0.02 um. So you must eliminate the dust contamination before you even start to measure anything.
Dear Mr. De Oliviera, thank you for your answer. I will read it.
Dear Mr. Rawle, I also asked another question relevant with this one. Can you look at it?
https://www.researchgate.net/post/Does_filtering_change_particle_diameter#58087264b0366d4eef6b4a62
Dear Ugur,
of course it is normal that a linear polymer even in a theta solvent at theta temperature ( a solvent with the same interactions as the segments themselves) will result in something like a eliipsoid sphere (depending an the possible an energetically favoured angles of the chemical groups). You should search for the keyword "gyration radius" which will lead to much more information.
http://www.tandfonline.com/doi/abs/10.1081/MA-120005804?journalCode=lmsa20
http://www.tandfonline.com/doi/abs/10.1081/MA-120005804?journalCode=lmsa20
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