Chemical Recognition in Nanofibers Made Possible with hyPIR Imaging
Incorporating nanocrystalline cellulose (NCC) into polyacrylonitrile (PAN) fiber changes the tensile property of PAN fiber. The goal is to identify the distribution of NCC on PAN fiber.
The peaks associated with NCC are acquired by taking PiFM spectra of pure NCC sample. The NCC peaks compared to the glass substrate are clearly identified. These peaks are used to bring out the subtle features from the hyPIR image taken of the PAN-NCC sample. Note that the strengths of peaks are as such: strong (1034, 1059, 1273 cm-1), medium (1103 cm-1), and weak (1167, 1212, 1323 cm-1).
The PiFM spectrum of a PAN-NCC samples clearly identifies the strong PAN peaks.
When the NCC sample is imaged at a wavenumber (946 cm-1) not associated with NCC peaks, NCC appears darker than the glass substrate whereas when it is imaged at a wavenumber (1260 cm-1) associated with NCC peaks, the PiFM image for NCC particles correlate well with the topography image.
The above images show the PiFM intensity map for the specified wavenumbers, which are associated with the NCC and PAN peaks. The images are displayed with different values of maximum intensity in order to bring out the PiFM features within the fiber structure. Note that NCC peaks at 1034, 1059, and 1271 cm-1 and PAN peaks at 1465, and 1738 at cm-1 are displayed with the same maximum intensity. The images at 1034 and 1059 cm-1 show the fiber being outlined from bright horizontal lines against the very strong substrate signal whereas the images at 1465 and 1738 cm-1 show the entire fiber being much brighter than the substrate. The image at 1103 cm-1 also reveals the horizontal PiFM features when the maximum intensity is lowered to 200. At 1271 cm-1, the PiFM signal for both the substrate and the overall fiber appear with roughly similar strength (as expected based on the spectra at the top of the page, which show peaks at 1273 cm-1 for both the glass substrate and NCC, albeit stronger for NCC) except for the brighter horizontal features observed at other NCC peaks. At the weak NCC peaks (1167 and 1324 cm-1), the maximum intensity has to be lowered to 150 to bring any PiFM feature on the fiber. Given that at the pure PAN peaks (1465 and 1738 cm-1), the whole fiber is more or less homogeneous in PiFM signal (without the strong horizontal features observed at NCC peaks), it is likely that the horizontal PiFM features observed at NCC peaks indicate the distribution of NCC on the PAN-NCC fibers.
These two images that superimpose the PiFM signals onto the topography shows that the PiFM signal at NCC peaks are associated with topographical ridges whereas there is no such correlation at a PAN peak (if anything, there is an inverse correlation where the PiFM signal at 1463 cm-1 is slightly lower at the ridges).