I am preparing CNT nanocomposite hydrogel. I have used PVP as surfactant. From the literature, I found that PVP is suitable to disperse CNT NPs in water, as PVP will wrap over CNT wall, but could not find any suitable proof for that. Other than TEM, is there any other way to prof that PVP is wrapped?
NMR+FTIR. Bound PVP will have substantially broadened peaks in NMR. You will need to be careful to remove the excess however. FTIR will give you the average coverage if you know your surface area. TEM will fail except in very special preparations. AFM will not be conclusive. STM could be conclusive with sufficient controls.
you can make a TGA of your system (PVP/CNT) and compare to pure CNT. After complete degradation, the difference corresponds to PVP.
you can solubilize your system (PVP/CNT without free PVP) in a deuterated solvent (organic or water, neutral or salt form for PVP). After cotton filtration, the NMR of the resulting black solution can show the non-adsorbed PVP (loop) on CNT.
The CD and FTIR can help. The SWCNTs have no signal for CD. I did not use the FTIR but I think it could be helpful. Please note that the carbon nanotubes can have some absorbance.
And, because the carbon nanotubes cannot be dispersed. And if you only add PVP and the carbon nanotubes can be dispersed, the only reason is that the PVP wrap on carbon nanotubes.
In the case of SWNTs, the characteristic Raman lines are very sensitive to local environment and interactions.
see for example - S.M. Keogh, et al., J. Chem. Phys. B, 109 (12): 5600-5607 (2005)
The temperature dependence of the Raman features can be correlated with TGA or DSC to further elucidate their origin.
This is less so in the case of MWNTs, but it should confirm the presence of the polymer and also and perturbation of the nanotube pi elctron system.
Do a TEM ! You would be able to see the coiled polymer structure wrapped around the nanotube !
Do you want to prove that PVP adsorbs on the surface of the MWCNT? For that you can indeed use Raman spectroscopy and XPS. However, PVP does not "wrap" around the nanotubes - this a myth. Check the abundant literature by Igal Szleifer and Rachel Yerushalmy-Rosen to that effect.
PVP is generally used as capping agent for nanoparticles and difference can be observed by fluorescence intensity measurement.
In my mind the best way to prove it (if this wrapping effect is real) would be AFM imaging after a clean deposition of the MWNT on a flat surface (spin coating or capillary drive deposition) .
Run 1H NMR. If you cannot see the PVP then it is sure that it is on. Measure the diffusion rate by PGSE NMR. If it is slower than that of the free PVP then it is partially on.
Of course there can be more complicated cases but first try this.
NMR+FTIR. Bound PVP will have substantially broadened peaks in NMR. You will need to be careful to remove the excess however. FTIR will give you the average coverage if you know your surface area. TEM will fail except in very special preparations. AFM will not be conclusive. STM could be conclusive with sufficient controls.
But with XPS you just can see covalent bonds... in this case you have non-covalent ones. I think that you should remove the CNTs from the PVP by centrifugation and wash them very well, and them analyse by FTIR and perform the TGA. The remaining PVA in the CNTs surface will be the one that establish some chemical interactions.
Is hard to demonstrate that is wrapped. But there are many methods to demonstrate the formation of an interface between the polymer and the nanotubes. You can do TGA , DSC, DMA or Raman, XPS, FTIR, DLS, and NMR to demonstrate it.
Demonstration of wrapped : saxs + sans modeling with a core-shell cylinder structure and GIFT analysis with a cylindrical analysis should do it
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