Modern Polymer Spect..

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Figure 2-1. Schematic structure of a side-chain liquid-crystalline
polymer.
. orientation mechanism of a liquid single crystal elastomer during cyclic deformation
and recovery.
Static and time-resolved spectroscopic data acquired both, by the conventional
rapid-scan and by the novel step-scan technique will be presented and interpreted in
terms of their individual applications.
2.2 Measurement Techniques and Instrumentation
Since the mid-l970s, FTIR spectroscopy has been widely used for polymer analytical
applications and for studies of time-dependent phenomena in chemical and
physical processes [ 141. With the current iinproveinent in electronics and data
acquisition procedures, the time resolution for such investigations with an acceptable
signal/noise-ratio is presently about 20 111s. Time resolutions far beyond this
value are not accessible by the conventional rapid-scan technique with continuous
mirror moveinelit without additional interferogram data manipulation. Thus, for
time-resolved, rapid-scan measurements, generally, the retardation time of the
moving mirror has to be considerably shorter than the time duration of the investigated
event (Figure 2-2a). In search of new approaches, stroboscopic techniques
have been proposed, where interferograms taken in the rapid-scan mode are subsequently
subjected to a sampling of reordered interferograin segments and have
thus led to an improvement in time resolution by a factor of about 500 [24, 251.
A further improvement in time resolution to the submicrosecond level has been
achieved with the step-scan technique 116, 26, 271. Here, the mirror is moved stepwise
and the optical retardation is held constant during sampling of the individual
interferogram elements. Thus, the time resolution is only limited by the response of