FTIR imaging

The FTIR imaging method was extended to the realtime acquisition of images from systems varying with time. Emphasis is given to the monitoring of the diffusion of a low molecular weight liquid crystal pentylcyanobiphenyl into a solid polybutyl methacrylate film (136). 

An imaging spectrometer made measurements of the visible and NIR absorption spectra of EVA copolymers. The NIR spectral images obtained clearly indicated that the EVA copolymers exhibited a high degree of chemical inhomogeneity (105). 

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The goal of our investigations was to characterise the morphology of the sample, and to determine the size and location of the PTFE and silicone oil phases by different methods [46,47], For phase characterization using Raman microscopy, no special sample preparation was necessary. For FTIR imaging, microtomed sections (5 pm in thickness) had to be prepared by cutting the sample with a diamond knife at — 80°C ("cryo-microtomy") to prevent smearing and to obtain flat surfaces. 

The Raman images in Figure 7 show that PTFE clusters in the sample are between 8 and 20 pm in diameter [46]. These results have also been confirmed by FTIR imaging and SEM [47]. 

In this example a polymer laminate film (for packaging) was examined, which was composed of nine layers (see Table 2), by both FTIR imaging and Raman line scan. For the IR measurements thin sections (5 pm) were cut. The central ethylene/vinyl acetate (EVA) copolymer layer is very soft, and holes can be seen in the visible image (Figure 12). 

Figure 12 IR transmission images of a polymer laminate. Left video image. Right IR image of the amide band (bright high COPA concentration). Only the COPA layers are visible in the FTIR image. The horizontal features in the middle layer are holes, originating during microtoming due to the material s softness.

Snively, C. M. and Koenig, J. L. (1998) Application of real time mid-infrared FTIR imaging to polymeric systems, diffusion of liquid crystals into polymers. Macromolecules 31, 3753-5. 

Each of these sampling analysis methods has advantages and disadvantages for FTIR imaging of polymeric systems as elucidated next. 

A thin film for FTIR imaging can be prepared by solvent casting. Solvent casting requires a solvent that dissolves the sample preferably at room temperature, which can be easily removed (high vapor pressure) without formation of bubbles in the sample film. Solvents such as chloroform (boiling point (bp.) 61.2°C), acetone... 

Figure 5.1 (a) FTIR image of a PB-E7 blend, (b) False color composite of absorbance distribution... 

Applications of FTIR imaging to complex polymer systems... 

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