Modern Polymer Spect..

78 2 Segnientril Mobility of Lipid Crystals uizd Licliri~-Cr)istulliiie Polvrwrs
0.07 -
0.06 ..
-
N 005 .*
Figure 2-47. Stress-strain diagram of
0 10 20 30 40 an elongation-recovery cycle of' the
STRAIN I"/]
reference elastomer at 27 "C.
0. 60
S
0. 40
0. 20
Figure 2-48. Order parameter/
strain-plot for the v(C-N)
I .
I I I I I I 1 I absorption corresponding to the
10 20 30 10 ' 40 30 20 10 elongation-recovery cycle shown
STRAIN [Yo] in Figure 2-47.
decrease in sample thickness based on the assumption of a constant sample volume
during elongation [30, 361. A more complex behavior is observed during the elongatioii-recovery
cycle of the LSCE system to a maximum strain of 45% at 27°C.
The corresponding stress-strain curve is shown in Figure 2-49 and has been subdivided
into different strain intervals. The order parameter of the v(C-N) absorption
derived from the spectra acquired during this mechanical treatment is presented
in Figure 2-50. Here too, the analogous strain intervals are indicated to assist
the correlation and interpretation of the mechanical and spectroscopic changes.
Due to the anisotropy of the starting material and the reorientation of the mesogens
during the mechanical treatment, specific assumptions in terms of the reference
direction were necessary. Thus, for the derivation of the order parameter during
elongation between 0 and 32% strain (intervals I and I1 in Figure 2-50), the deformation
direction during the second crosslinking step (which is perpendicular to the
applied deformation in the rheo-optical experiment) has been chosen as polarization
reference direction. Beyond the inversion point of S = 0, the machine direction of
the rheo-optical experiment is applied as polarization reference (interval 111). During
recovery this procedure is reversed. Therefore, the order parameter always has
a positive value throughout the whole experiment. From Figure 2-50 the following
picture can be derived for the orientational changes taking place during the
elongatioii-recovery cycle: