FTIR Imaging of Polymeric Materials

Department of Chemical Engineering, Imperial College London, London, UK 

In polymer processing, whether it is a blending, annealing or diffusion process, it is vital to characterize the chemical composition and spatial distribution of the materials involved. Fourier transform infrared (FTIR) spectroscopy has traditionally been used as a powerful nondestructive material identification method, as well as an important tool to study intermolecular interactions and different polymer morphologies. With the introduction of infrared (IR) microscopes and array detectors, chemical imaging using FTIR spectroscopy has become an established tool in polymer analysis. 

In this chapter, we introduce the principles of the FTIR imaging method and some of the recent applications of FTIR imaging in the study of polymeric materials. This includes an introduction to the general approach of FTIR image acquisition, the transmission and attenuated total reflection (ATR) modes of measurement, the different approaches of measuring liquid and solid samples, the considerations needed to be taken in order to obtain a reliable and accurate imaging measurement and also some of the new opportunities that exist for FTIR imaging. 

Each of the measured spectra becomes a pixel which, when placed together, forms the final image (see Fig. 7.1). The spectral imaging data is therefore a three-dimensional data cube the X and Y axis of the array of pixels and the wavenumbers in the spectrum. A polymer that contains different functional groups will produce specific spectral bands, which can then be used as a marker for that polymer species. The spatial distribution of the various polymer 

Polymer Morphology Principles, Characterization, and Processing, First Edition. Edited by Qipeng Guo. 2016 John Wiley Sons, Inc. Published 2016 by John Wiley Sons, Inc. 

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Kazarian SG, Chan KLA (2003) FTIR imaging of polymeric materials under high-pressure carbon dioxide. Macromolecules 37(2) 579-584... 

FTIR IMAGING OF POLYMERIC MATERIALS 7.5 RECENT APPLICATIONS 7.5.1 Polymer Blends... 

The first reported application of FTIR imaging to polymeric materials was the imaging of a cross-section of a laminated polymer film. The adhesive layer between... 

IR analysis can be applied to surfaces [3] and pyrolyzed fragments of polymeric materials [4] for purposes of identification. In particular, FTIR microscopes are useful for evaluating micron-sized regions of fiber, film, and coating samples. The FTIR microscope can be used as a conventional optical microscope, but, in addition, an IR spectrometer is attached to the microscope. It is possible to direct the image beam through the spectrometer and collect sample spectra. Of particular use is the fact that silicon wafers, the substrates used to build most microelectronics, are transparent in the IR. Thus, this substrate is ideal for use in thin film analysis. 

This section introduces a novel application of IR spectroscopy, namely IR imaging, and the specific sampling technique of attenuated total reflectance (ATR). FTIR imaging in ATR mode allows one to visualize the spatial distribution of different components in polymeric materials and to study directly the effect of high-pressure CO2 on this distribution. This novel approach should benefit polymer scientists studying polymer blends and their processing with SCCO2. 

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