FTIR技术在高分子薄膜表征中的应用

Use of FTIR in polymeric thin films
Feichen Yang
FTIR(Fourier transform infrared spectroscopy) is a technique that uses Fourier transform to convert the raw data of infrared absorption or transmission into a infrared spectrum. Essentially, it measures the energies that are correspondent to the vibration of atoms in molecules or macro-molecules.
The simplest application of FTIR on polymers is that FTIR can help to identify the functional groups in polymers. By comparing the ‘fingerprint region’of a obtained sample to that of a standard sample, researchers can also identify an unknown polymer.
In the mean time, researchers can use FTIR to measure the concentration of a certain functional group, to determine the extent of reaction. For example, Helmut Reinecke et al[1] used the integrated IR absorbance in 1450-1580 cm-1that increases with the number of reaction circles to prove the increasing number of monomers in the polymer thin film.
Besides that, when it’s used specifically on polymers, FTIR have some unique applications. First, since the bond bending and vibrating motions of atoms are not completely irrelevant with other atoms nearby, FTIR can help determine the tatcticity of polymers. For instance, Dalmo Mandelli et al[2]used FTIR with multivariate calibration to determine the tacticity of polypropane. Using similar principle, FTIR can also help determine the conformation of polymer chains or the crystallinity of a polymer. By using FTIR spectroscopy and curve-fitting techniques, Yoshio Inoue et al[3] developed a procedure to determine the crystallinity of p oly(ε-Caprolactone).
If we use polarized infrared light as the incident light, FTIR can determine the orientation of polymer in thin films or in polymer brushes. Since light can only be absorbed when the direction of light polarization is parallel to the vibration transition moment, the polarized light can only be absorbed by vibration in certain directions. By comparing parallel FTIR spectrum and the perpendicular FTIR spectrum of a polymer film sample, one can determine whether the polymers are randomly deposited or aligned. For example, John F Rabolt et al[4] used polarized FTIR to determine the orientations of electrospun Nylon-6 nanofibers.
In conclusion, by determine the vibration mode of atoms in polymeric thin films, FTIR could be used to identify polymer, monitor reaction, determine the tacticity of polymer, and measure the orientation and its distribution.
References:
[1] Lomadze, N., Perez, M., Prucker, O., Ruhe, J., & Reinecke, H. (2010). Step-and-Repeat Assembly of Molecularly Controlled Ultrathin Polyaramide Layers. Macromolecules, 43(21), 9056-9062.
[2] Ozzetti, R. A., De Oliveira Filho, A. P., Schuchardt, U., & Mandelli, D. (2002). Determination of tacticity in polypropylene by FTIR with multivariate calibration. Journal of applied polymer science, 85(4), 734-745.
[3] He, Y., & Inoue, Y. (2000). Novel FTIR method for determining the crystallinity of
poly (ε‐caprolactone). Polymer international, 49(6), 623-626.
[4] Lee, K. H., Kim, K. W., Pesapane, A., Kim, H. Y., & Rabolt, J. F. (2008). Polarized FT-IR study of macroscopically oriented electrospun nylon-6 nanofibers. Macromolecules, 41(4), 1494-1498.。