increased by 0–6 J/cm
2 as the irradiation time increased. However, the intensity
decreased by 6–10 J/cm
2 as the irradiation time further increased. The extents of the
increase in the range 0–6 J/cm
2 ranked as follows: THF 100
C > DMAc
250
C > THF 250
C > DMAc 100
C. In addition, the extents of reduction in
the range 6–10 J/cm
2 ranked as follows: THF 250
C > DMAc 250
C > DMAc
100
C > THF 100
C. The peak intensity was nearly constant because it did not
depend on the temperature and casting solvent conditions. Meanwhile, the intensity
of peak b decreased as the LPUV irradiation time increased. The reduction was in the
order, THF 250
C > THF 100
C > DMAc 250
C > DMAc 100
C, and showed
greater dependence on the casting solvent than on the heat-treatment temperature.
This reduction also depended on the highly volatile preparation conditions. The peak
intensity of the 6FDA-TeMPD films prepared in the DMAc solvent was not affected
by irradiation at 1 J/cm
2 LPUV (Fig. 11). In addition, a time lag in the reduction was
observed. Therefore, the film preparation conditions affected the LPUV irradiation
effect.
The photoreaction mechanisms of all 6FDA-TeMPD films prepared under
LPUV irradiation are schematically shown in the absorbance spectra (Fig. 9).
The electron-donating benzene ring and the electron-accepting imide ring formed
CTCs between the polymer chains in the MLP structure. Therefore, the photoreaction between the C=O group of the imide ring and the CH 3 group under LPUV
irradiation occurred in one direction, resulting in the formation of hydroxyl group
O-H on the side 6FDA-TeMPD polymer chain. The symmetrically structured
polymer (6FDA-TeMPD) exhibited combinations with alternating sequences on
both cross sides. The increase in the intensity of peak a was determined by CTC
formation, which is a measure of polymer cohesiveness. On the other hand, the
reduction in the intensity of peak b is attributed to the decrease in the photoreaction
of the C=O group. Therefore, the fluorescence spectra of all 6FDA-TeMPD films
were obtained to characterize the CT interactions and determine the extent of CTC
production, given that LPUV irradiation affects the condensation of polymer
segments.
Figure 14 shows the fluorescence spectra of all 6FDA-TeMPD films irradiated
at 0, 1, and 10 J/cm
2 LPUV. All 6FDA-TeMPD polyimide films exhibited an
emission spectral band at 470 nm after excitation at 325 nm. This band is attributed
to the intramolecular interactions of the aromatic polyimide that contains an
alternating sequence of electron-rich donor and electron-deficient acceptor molecules. Therefore, CTC formation and polymer cohesiveness can be determined via
fluorescence spectroscopy. The maximum peak emission wavelength, λ max , was
471 nm for the films thermally treated at 100
C (THF 100
C and DMAc 100
C),
while λ max of the films thermally treated at 250
C (THF 250
C and DMAc
250
C) was 474 nm. The λ max depended on the thermal treatment temperature. In
addition, the λ max of all prepared films increased to approximately 478 nm as the
LPUV irradiation time increased. This result indicates that the energy needed to
form CTCs was decreased by LPUV irradiation. LPUV irradiation depends on the
chemical structure and polymer cohesiveness. This result is consistent with those
shown in Fig. 9.
18 Photoalignment of Liquid Crystal Molecules Using Fluorine-Containing. . .
509
2 as the irradiation time increased. However, the intensity
decreased by 6–10 J/cm
2 as the irradiation time further increased. The extents of the
increase in the range 0–6 J/cm
2 ranked as follows: THF 100
C > DMAc
250
C > THF 250
C > DMAc 100
C. In addition, the extents of reduction in
the range 6–10 J/cm
2 ranked as follows: THF 250
C > DMAc 250
C > DMAc
100
C > THF 100
C. The peak intensity was nearly constant because it did not
depend on the temperature and casting solvent conditions. Meanwhile, the intensity
of peak b decreased as the LPUV irradiation time increased. The reduction was in the
order, THF 250
C > THF 100
C > DMAc 250
C > DMAc 100
C, and showed
greater dependence on the casting solvent than on the heat-treatment temperature.
This reduction also depended on the highly volatile preparation conditions. The peak
intensity of the 6FDA-TeMPD films prepared in the DMAc solvent was not affected
by irradiation at 1 J/cm
2 LPUV (Fig. 11). In addition, a time lag in the reduction was
observed. Therefore, the film preparation conditions affected the LPUV irradiation
effect.
The photoreaction mechanisms of all 6FDA-TeMPD films prepared under
LPUV irradiation are schematically shown in the absorbance spectra (Fig. 9).
The electron-donating benzene ring and the electron-accepting imide ring formed
CTCs between the polymer chains in the MLP structure. Therefore, the photoreaction between the C=O group of the imide ring and the CH 3 group under LPUV
irradiation occurred in one direction, resulting in the formation of hydroxyl group
O-H on the side 6FDA-TeMPD polymer chain. The symmetrically structured
polymer (6FDA-TeMPD) exhibited combinations with alternating sequences on
both cross sides. The increase in the intensity of peak a was determined by CTC
formation, which is a measure of polymer cohesiveness. On the other hand, the
reduction in the intensity of peak b is attributed to the decrease in the photoreaction
of the C=O group. Therefore, the fluorescence spectra of all 6FDA-TeMPD films
were obtained to characterize the CT interactions and determine the extent of CTC
production, given that LPUV irradiation affects the condensation of polymer
segments.
Figure 14 shows the fluorescence spectra of all 6FDA-TeMPD films irradiated
at 0, 1, and 10 J/cm
2 LPUV. All 6FDA-TeMPD polyimide films exhibited an
emission spectral band at 470 nm after excitation at 325 nm. This band is attributed
to the intramolecular interactions of the aromatic polyimide that contains an
alternating sequence of electron-rich donor and electron-deficient acceptor molecules. Therefore, CTC formation and polymer cohesiveness can be determined via
fluorescence spectroscopy. The maximum peak emission wavelength, λ max , was
471 nm for the films thermally treated at 100
C (THF 100
C and DMAc 100
C),
while λ max of the films thermally treated at 250
C (THF 250
C and DMAc
250
C) was 474 nm. The λ max depended on the thermal treatment temperature. In
addition, the λ max of all prepared films increased to approximately 478 nm as the
LPUV irradiation time increased. This result indicates that the energy needed to
form CTCs was decreased by LPUV irradiation. LPUV irradiation depends on the
chemical structure and polymer cohesiveness. This result is consistent with those
shown in Fig. 9.
18 Photoalignment of Liquid Crystal Molecules Using Fluorine-Containing. . .
509