Modern Polymer Spect..

2.7 Orientation oj Liquid Crystals Uiider Meclimiicul Forces 75
Figure 2-44. (a) Principle of rheo-optical FTIR spectroscopy of polymer films. (b) Variabletemperature
stretching machine for rheo-optical FTIR and FT-Raman spectroscopy. (A) stretching
machine; (B) sample transfer mechanism; (1) stress transducer; (71 strain transducer: (3) film sample;
k4'1 sample clamps [17, 181.
for new experimental techniques to characterize transient structural changes
during mechanical processes. With the advent of rapid-scanning FTIR spectroscopy,
rheo-optical measurements have been applied to obtain data on the orientation,
conformation, and crystallization during mechanical treatment of a wide
variety of polymers [14, 17-20, 1121. The experimental principle of rheo-optical
FTIR spectroscopy is based on the simultaneous acquisition of polarization spectra
and stress-strain diagrams during deformation, recovery or stress-relaxation of
the polymer under investigation in a miniaturized, computer-controlled stretching
niachine which fits into the sample compartment of the spectrometer (Figure 2-44).
The impleinentatioii of a heating cell as a closed, nitrogen-purged system offers the
additional possibility to study the above mechanical phenomena under controlled
temperature conditions ( i 0.5 "C) up to 200 "C. The electromechanical apparatus,
the experimental procedure and the evaluation of the relevant parameters from
the polarization spectra series have been described in detail in several publications
[17-20, 1121.
2.7.2.3 Near-Infrared Spectroscopy
For samples exceeding the thickness accessible for ti-ansmission measurements
by mid-infrared spectroscopy, near-infrared (NIR) spectroscopy may be used as
an alternative technique [ 1131. Adjacent to the conventional mid-infrared region
14000-400 cni-l) the NIR region covers the interval from about 12 500-4000 cm ' .