As shown in Figure 3.20, the dynamic in-phase and quadrature spectra, and the corresponding phase rotation plot of this material indicate that different segments of the molecules have different response times to the mechanical strain as reflected by the phase delay between different regions. For the broad carbonyl band, detailed band assignment can be made. The 1730cm-1 absorption band (species I) is assigned to the “free” (non-H bonded) carbonyl of the urethane segment. This type of urethane is found embedded in the soft siloxane matrix. It is used as a marker to monitor the dynamic behavior of the soft segment. The dynamic FT-IR data show that response of this segment is approximately in-phase with the response of the mesogen (-CN stretching band) since both of them have strong intensity on the in-phase spectrum. The 1715cm-1 absorption band (species II) is assigned to the carbonyl of the urethane species that are found in the interfaces between the “hard” and the “soft” segments. Finally, the 1702cm-1 absorption band (species III) is assigned to the H-banded carbonyl of the urethane “hard” segments. Thus it can be concluded that the presence of infrared signatures in the dynamic spectra is an indication of the fact that the application of mechanical deformation induces orientation to both “hard” and “soft” segments of this type of
$$lc polymer. The side chain mesogens ate free to deform in the elastic soft segment and the responses of different types of “hard” urethane segments can be examined by analyzing the carbonyl spectral region. The reorientation behavior of the “hard” and “soft” segments can be further deconvolved using 2D correlation spectroscopy, which is the subject of Chapter 7 of this book.