## 3 Results and Discussion
### Photoalignment of PAA and P(Az-CB) Films
#### 3.2.2 In-Plane Photoalignment of P(Az-CB)  
It should be interesting to grasp the effect of a coated polymer layer on the photoalignment behavior. However, the Az mesogen of the PAz oriented vertically and horizontally after annealing with and without the polymer coat, respectively, and it was impossible to make direct comparisons. Therefore, in this section, the photoalignment process is compared using P(Az-CB) that adopts a planar orientation without the topcoat [22; 39]. As mentioned in the introductory remark, the copolymerization ration of Az:CB = 0.27:0.73 gives a random planar orientation. In fact, the absorption spectra of P(Az-CB) before and  
Figure 7: Polarized UV-visible absorption spectra of PAz film (thickness: 100 nm) coated with PBMA (**a**) and PVP (**b**). Blue and red lines indicate spectra taken perpendicular (\(\perp\)) and parallel (//) to the direction of exposed LPL in (**c**) and (**d**), GI-SAXS data are shown for the photoaligned PAz coated with a PBMA layer. after annealing hardly results in any changes, indicating that this copolymer provides a random planar orientation without a polymer topcoat. LPL irradiation was conducted at 70-130 \({}^{\circ}\)C. Figure 8a shows the polarized UV-visible absorption spectra for P(Az-CB) without a topcoat irradiated at various temperatures. Spectrum measurements were performed after cooling to room temperature. The \(\pi\pi\)\(\pi^{*}\) bands of Az and CB were positioned around 360 and 290 nm, respectively. These spectra were obtained after LPL irradiation at a dose of 1.0 J cm\({}^{-2}\). The increase in \(S\) was saturated at 200 mJ cm\({}^{-2}\), and further irradiation did not affect the degree of in-plane optical anisotropy. The dotted and solid lines correspond to the polarized spectra in the perpendicular and parallel directions of the LPL, respectively. In all spectra, the dichroic ratios (\(A_{\perp}/A_{//}\)) obtained for the Az and CB \(\pi\pi\)\(\pi^{*}\) bands coincided with each other under all conditions, showing that the two mesogens were photoaligned in a highly cooperative manner. In Figure 8b, the order parameter after the above LPL irradiation conditions was plotted as a function of the temperature for a P(Az-CB) film without a topcoat (black circle) on a quartz plate, a PVP-coated P(Az-CB) film (red triangle) and a P(Az-CB) film prepared on a PVP-coated substrate (blue diamond). The last film constitution was examined to grasp the influence on the underlying substrate surface. In these evaluations, the photoalignment procedure was achieved at each target temperature and then cooled down to room temperature for spectral measurements. The in-plane \(S\) increases with the increase in temperature until reaching the isotropization temperature (\(T_{\text{iso}}\)) of 113 \({}^{\circ}\)C. The extent of S enhancement is strongly dependent on the film constitution. Among the three types of films, the pure P(Az-CB) film provided the highest in-plane \(S\) at all temperatures, with S exceeding 0.5 above 100 \({}^{\circ}\)C. However, this film exhibited film damage (dewetting) above 113 \({}^{\circ}\)C (indicated by \(T_{\text{iso}}\) in Figure 8b), and the evaluation of \(S\) above this temperature was not feasible. Interestingly, when the P(Az-CB) film was formed on a polymer layer of PVP, the film was stable enough to evaluate \(S\) up to 130 \({}^{\circ}\)C. The dewetting seemed to be  
Figure 8: (**a**) Polarized UV-visible absorption spectra of P(Az-CB) film (thickness: 100 nm) without topcoat after LPL irradiation at various temperatures. Dotted and solid lines correspond to spectra taken perpendicular and parallel with irradiated LPL. (**b**) In-plane order parameter of P(Az-CB) films. Black, red and blue symbols correspond to data for pure P(Az-CB) film, P(Az-CB) film coated with PVP layer, and P(Az-CB) film formed on PVP underlayer, respectively. A scheme below b indicates the relationship between the film constitution and resulting in-plane \(S\).