Hi everyone. I have been doing some research on polymer complexes. I saw many of papers measured the Rh of the complexes with DLS and Rg with SLS. But the problem concerned me is that when we measure a dn/dc value of a certain kind of polymer, we can obtain it by measure several solutions in different concentration. However,solutions of polymer complexes are not homogeneous, how can i determine the dn/dc value then? and how did others determine it and obtain the Rg value? thanks.
dn/dc is a technique for homopolymer, is the sample is complex the technique is not useful. The measurement is with a dilute solutions of homopolymer
As long as your complex is stable (does not change composition) over a certain concentration range you can measure the refractive index of those solutions, extrapolate to zero concentration and thus calculate the dn/dc. There are publications where dn/dc of micellar solutions were determined above their critical micelle concentration. If your complex is not stable during the time of measurement or forms species of different size you will not be able to calculate the absolute value of dn/dc. Some people use the signal of the refractive index detector and measure dn/dc in a "GPC mode". The deficiency of this method is that it assumes all of the sample elutes within the boundaries of the peak measured (i.e. 100 % recovery). Hopefully this helps. Good luck.
Others important aspect have to be taken account. The dn/dc, can be found by the use of a differential refractometer, and If the polymer sample is soluble in various solvents you have to choose the solvent in which the value dn/dc is the biggest.
Dear Chao Wang,
my first question is whether you need dn/dc at all. From you last sentence I get the Impression that you do not like to determined molar mass , but Rg only.
If this is the case you do not Need dn/dc at all, as RG is determined from the slope of the angular dependence.
Best regards
Wolfgang
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