Besides SEM or TEM-related techniques, does anyone have any suggestion about other methodologies or instrumental techniques that might help in proving that the nanofibers that I obtained by coaxial electrospinning (aka co-electrospinning) are actually core-shell structured? Maybe X-ray difraction might be useful, though I am not sure. I would appreciate suggestions, including literature, on this topic.
It depends also on the composition of your potential hybrid core shell material. A possible route to prove the core Shell nature could be a difference in the solubility in e. g.alkaline or acidic media or also different solubilities in different solvents. If this is the case you can use TEM combined with EDX to identify the nature of your residues.
Extended X-Ray Absorption Fine Structure (EXAFS) and X-ray Absorption Near Edge Structure (XANES)
Hey, You could XPS (Xray photo-electron spectroscopy) to confirm the absence of core material on the fiber surface. This data along with XRD and IR spectroscopy can confirm that you have both core and sheath material in your fiber and the core material is present only in the core and absent on the sheath. I hope this helps. Further, you could differentially stain the core or the sheath with a fluorescent dye.
If you need a more specific answer, then let us know a bit more about the sample.
I suggest to use any technique that analyze just your surface of electrospun fibers. XRD could be used for crystalline materials. so you should be sure that your structure is crystalline. I think that you should have a TEM image (or SEM from the cross section of nanofiber), then measure the diameter of the sheath. now you can select an surface elemental analysis technique that analyses only the sheath. so you can demonstrate to have a core-shell nanofiber.
some of the surface elemental analysis technique: XRD, XPS, XRF, SAXD, EAXD, iSS
which analyze various depth from your sample.
Depending on the natural contrast (electron density difference between the core and shell materials), you can embed a sample of fibers in epoxy resin and either: microtome thin cross sections for TEM (which works wonderfully for me, but a microtome and even TEM may not be readily available for you). Recently in my lab, we have adapted this technique to be used for SEM. For SEM, you can embed your sample in resin and slice it with a razor for cross sections as well. Again, this won't really work if your core and shell materials are too similar.
Even easier SEM method- if your fiber mats are strong enough that you dip a piece of fiber mat in liquid nitrogen and literally snap it in half to expose clean breaks through fibers. It's helpful if you have the SEM stubs that have a 90 degree edge so you can easily set your sample with the 'broken edges' normal to the stub.
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