Has anyone tried to establish the RI of CNTs by measuring the RI of several suspensions (different concentrations)?
I've tried to do that, by following this protocol: http://www.pct.hu/wsp_images/refind.pdf. In theory, you measure different concentrations of the tested samples in the solvent of choice and then, by extrapolation, find the RI of pure sample (assuming that its RI would be RI of the suspension having 100% concentration). Of course, this theory requires some simplifications (e.g. no strong solvent-solute or solute-solute interactions), but I thought it might work for the CNTs.
However, what I'm getting is quite surprising - instead of linear increase of RI with increasing concentration, what I observe is linear drop. Any ideas what would be the reason for that? I'm thinking that maybe the CNTs absorb most of the light, thus falsifying the results?
Any input would be very much appreciated.
Do you mean dispersed or dissolved? This approach assumes that no dissolution occurs. My CNTs are highly oxidized and well dispersed in the solvent (Zeta potencial of approx -30mV). Still, no luck there.
Dissolved. Now I’ve read the attachment, I’m absolutely certain. The material must be soluble - not a suspension - to work.
Correct me if I'm wrong, but if that's used as a method for establishing RI for size measurements via DLS method, then if the particles were to dissolve, it would be of no use. At least, that's how I understand that. From the referenced article by Saveyn (see attached) I got that it works for stable suspensions of particles.
The Saveyn article refers to dissolved material. A suspension will lose light exactly as you indicate and the amount of light lost is explained by the Beer-Lambert law (proportional to the projected area of suspended particles). Also RI of the particles is not required for an intensity distribution in DLS - only the RI of the continuous phase.
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