It is known to all that Zimm plot can be used to measure gyration radius of polymers. During the deduction of Zimm plot, no restriction has been made to the polymer. So I assume I can use Zimm plot to measure Rg of polyelectrolytes.
However, many reseachers use SANS (instead of static light scattering) to measure Rg of polyelectrolytes in dilute solution, e.g. Conformation and dynamics of flexible polyelectrolytes in semidilute salt-free solutions.
I'm confused. I hope you can share your idea about this question.
Chenxi Liang
In theory you can, but you have to have sufficient scattering that will come from:
- Sufficient size/molecular mass
- Concentration (you vary this in a Zimm plot anyway)
- Optical contrast (sufficient contrast between material and continuous phase)
Also you need to be able to relate the molecular mass of the system to Rg and this will depend on the (assumed) shape of the system - rod, coil etc. Biggest factor is scrupulous cleanliness of the samples. You can't underestimate this factor for a Jim Zimm plot. Also see the attached.
Hello Chenxi Liang
in order to detect an Rg there must be enough change in scattering intensity versus angle. For very small objects, the change is very small. In many practical experimental light scattering setups this typically means an Rg of ~15nm is the best (=smallest) possible for visible light,
By using neutrons, the wave length is 1-2 orders of magnitude smaller, so you can "see" the angular change for smaller particles / objects.
[More technically, it is the wave-vector or q-range which determines the minimal Rg. However, I think in this case, the wave length might help to illustrate this easier.]
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