Article pubs.acs.org/Langmuir
Birefringent Pattern Formation in Photoinactive Liquid Crystalline Polymer Films Based on a Photoalignment Technique with TopCoating of Cinnamic Acid Derivatives via H‑Bonds Nobuhiro Kawatsuki,* Ryosuke Fujii, Yu Fujioka, Satoshi Minami, and Mizuho Kondo Department of Applied Chemistry, Graduate School of Engineering, University of Hyogo, Shosha, Himeji 671-2280, Japan S Supporting Information *
ABSTRACT: The application of a top-coating of 4-methoxy cinnamic acid (MCA) onto a photoinactive liquid crystalline polymeric film containing benzoic acid (BA) side groups (P6BAM) is shown to enable thermally stimulated, photoinduced reorientation of the polymer structure. Annealing the MCA-coated P6BAM films leads to H-bond formation between BA and MCA, which also effectively smooths the film surface. Exposure to linearly polarized (LP) UV light initiates axis-selective photoreaction of the MCA groups; subsequent thermal treatment in the LC temperature range of P6BAM amplifies molecular reorientation of the BA side groups, while simultaneously eliminating the MCA molecules. Selective inkjet coating of MCA provides a facile route for the fabrication of patterned, oriented, and rewritable P6BAM films with multiple controlled alignment directions.
1. INTRODUCTION Photoalignment using photosensitive polymeric films is widely applicable to liquid crystalline (LC) display devices, optical functional films, and polarization diffraction devices.1−7 Conventional photoalignment techniques exploit a surfacealigning effect to achieve molecularly oriented structures of LC and polymeric films: in this method, a thin surface-alignment layer on a substrate undergoes axis-selective photoreaction when exposed to linearly polarized (LP) light, changing the structure of the layer and controlling the homogeneous orientation of LCs, polymerizable LCs, and LC polymers (LCPs) on the alignment layers.1−4,8−12 Alternatively, direct orientation of polymeric films can be achieved using photoalignable LCPs: these contain functional groups that respond to exposure to LP light and, in some cases, can be thermally stimulated to undergo self-organization.13−19 In our previous work, we have focused on combining thermal treatment with LPUV light exposure to induce molecular reorientation of photoresponsive LCPs:5,20 among the LCPs that we have studied, polymethacrylate with cinnamic acid (CA) side groups has produced particularly noteworthy results, exhibiting significant photoinduced molecular reorientation.21 However, in oriented films of these photoalignment materials, subsequent exposure to UV light can further alter their optical and mechanical properties because the photosensitive moieties remain in the film. The formation of H-bonds between side groups in certain polymeric and functional low-molecular-weight materials has been reported as a method for introducing LC characteristics and functionalities into the materials.22−25 The doping of various species of monomeric azobenzene derivative into nonphotoreactive polymeric films via H-bonding has been © XXXX American Chemical Society
explored as a possibility for enabling photoinduced molecular orientation and surface relief formation (SR).26−29 Additionally, the use of materials that may form ionic- or halogen-bonds has also been investigated with a view to introducing similar functionality into non-LC materials.30,31 We previously investigated photoinduced orientation of composite films consisting of a photoinactive polymethacrylate with a benzoic acid (BA) side group (P6BAM in Figure 1) and photo-
Figure 1. Chemical structures of P6BAM and MCA.
responsive low-molecular-weight materials such as CA or Nbenzylideneaniline (NBA) derivatives, where H-bonding between BA and CA/NBA side groups was shown to enable axis-selective photoreaction, creating a simple route to photoalignment of the P6BAM film via thermally stimulated and photoinduced molecular orientation.32,33 Additionally, the reoriented films exhibited significant photodurability, attributed to the thermal elimination of photosensitive CA (NBA) during the reorientation process.32 Recently, a new strategy for photoalignment has been demonstrated in several studies, following the discovery that the free-surface (air-side) condition can control the orientation of the interior structure in a polymeric film.34−41 Seki et al. Received: January 16, 2017 Revised: February 11, 2017 Published: February 14, 2017 A
DOI: 10.1021/acs.langmuir.7b00079 Langmuir XXXX, XXX, XXX−XXX
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Langmuir observed that a selectively segregated, azobenzene-containing polymeric thin film at the free surface was able to align an interior, nonphotosensitive layer in both polymer blends and diblock copolymers.34−39 In some of these studies, precise patterns of the photoresponsive surface film have been coated using inkjet to control the orientation direction of the photoinactive LCP film.37−39 In other works, facile preparation of a photoalignable LCP film has been achieved by coating phenylamine derivatives onto a polymethacrylate film with phenylaldehyde side groups, in which the two species reached to form photoalignable NBA side groups in selectively coated areas.40 Furthermore, by coating aromatic molecules onto LC polymethacrylate films with NBA side groups, easy control of planar and out-of-plane orientations has been demonstrated, with selective, photoinduced in-plane reorientation only occurring in the planar areas.41 As mentioned above, functional low-molecular-weight species can form H-bonds with appropriate side groups in polymers, and the selective introduction of these mobile, photosensitive moieties into photoinactive LCP films would be expected to provide a route toward patterned, photoalignable LCP films. On this basis, this Article describes effective photoinduced orientation and patterned alignment of a P6BAM film by applying a top-coating of 4-methoxy cinnamic acid (MCA in Figure 1). In this study, a combination of photoinduction and thermally stimulated reorientation was used: the coated MCA molecules, which form H-bonds with the BA side groups in P6BAM, undergo axis-selective photoreaction on light exposure, and subsequent thermal treatment is found to generate reorientation of the BA side groups of the P6BAM film in the MCA-coated regions. The influences of the coated amount of MCA, prebaking parameters, and photoexposure conditions on the reorientation behavior are investigated. Furthermore, selective coating of MCA by inkjet is shown to provide a facile route to the fabrication of photoinduced, birefringent P6BAM film patterns, and successful erasing and its rewriting of the pattern on the same film are demonstrated.
DR =
A⊥ − A A⊥ + A
(1)
where A∥ and A⊥ are the absorbances parallel and perpendicular to polarization (E) of LP 313 nm light, respectively. The surface topology was evaluated using an optical surface profiler (VertScan2.0 R3300, Ryoka Systems Inc., 235 μm × 176 μm area). Birefringence of the reoriented film was measured with a polarimeter (Shintech OPTIPRO 11-200A) at 517 nm.
3. RESULTS AND DISCUSSION 3.1. Fabrication of Photosensitive P6BAM Films Coated with MCA. Figure 2a plots the UV−vis absorption
Figure 2. UV−vis absorption spectra of 200 nm thick P6BAM films coated with MCA using various sublimation times. (a) As-coated films and (b) films prebaked at 110 °C for 2 min. Inset figure in (b) plots MCA content in the film as a function of sublimation time.
spectra of P6BAM (initial thickness: 200 nm) films after sublimation coating of MCA for time periods between 0 and 5 min. A broad absorption band appeared at 320 nm after coating the MCA, with a magnitude dependent on the sublimation time. The deposited MCA molecules were found to crystallize on the P6BAM surface, leading to a significant increase in the average surface roughness, Sa, of the film as shown in Figure 3a and b (increase in Sa from 0.79 to 24.7 nm after 3 min-coating time), and polarized optical microscope (POM) observation showed the formation of small crystals of MCA (inset in Figure 3b). The MCA thickness was measured to be approximately ∼50 nm. When the MCA-coated films were prebaked at 110 °C for 2 min, the absorption band of MCA was clearly observed, and the absorbance was shown to decrease slightly (Figure 2b). The process was found to flatten the film’s surface without scattering, although the overall Sa was slightly more uneven than the initial P6BAM film (Figure 3c, Sa = 0.91 nm). Additionally, the thickness of the prebaked films increased by approximately 20 nm as compared to the initial one (Figure S1). As such, we can conclude that MCA molecules penetrated into the P6BAM film upon prebaking, while the slight unevenness can be attributed to the rough structure of the MCA crystals before prebaking. Furthermore, the amount of MCA in the film was found to increase with increasing sublimation coating time, but the total amount was measured to not exceed 15 wt % (inset in Figure 2b), which is estimated by comparison with P6BAM/MCA composite films reported in other studies.32 As the penetration depth of MCA into P6BAM is limited, some MCA crystals were found to remain on the film when the sublimation coating time exceeded 5 min. The thermal penetration of MCA into the P6BAM film is expected to be accompanied by the formation of H-bonds between MCA and BA side groups. When a MCA-coated film was immersed in n-butanol before baking, the absorption band of MCA was found to diminish (Figure 4a), indicating
2. EXPERIMENTAL SECTION 2.1. Materials. MCA and all solvents were used as-received from Tokyo Kasei Chemicals. P6BAM, which exhibited a nematic phase between 144 and 177 °C, was synthesized by a process previously reported in the literature.22 The number-average molecular weight and polydispersity were 58 000 g/mol and 3.05, respectively. 2.2. Film Preparation and Photoreaction. P6BAM thin films (thicknesses of 200−600 nm) were prepared by spin-coating a tetrahydrofuran (THF) solution of the polymers (1.8−7.5 wt/wt %) onto quartz or CaF2 substrates. MCA was coated on P6BAM films either by sublimation at 200 °C, or by inkjet coating performed using a LabJet-1000 (MICROJET Co. Ltd.) precision printer from dimethyl sulfoxide (DMSO) solution (0.3 wt/vol %) at 30 °C. After being coated, the film was prebaked at 110 °C for 2 min to allow the MCA molecules to penetrate into the film. Photoreactions were carried out using a high-pressure Hg lamp equipped with a glass plate placed at Brewster’s angle, and a 313 nm band-pass filter (Asahi Spectra REX-250), yielding a light intensity at 313 nm of 10 mW/cm2. After photoirradiation, the films were annealed at 170 °C for 10 min to thermally stimulate molecular reorientation. 2.3. Characterization. For a measure of the photoinduced optical anisotropy, the photoinduced in-plane dichroic ratio (DR) was evaluated from the polarization absorption spectra with a Hitachi U3010 spectrometer equipped with Glan−Taylor polarization prisms, which is estimated as B
DOI: 10.1021/acs.langmuir.7b00079 Langmuir XXXX, XXX, XXX−XXX
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Figure 3. Three-dimensional image of the surface topology (235 μm × 176 μm) and the surface roughness (176 μm line) of the MCA-coated P6BAM film (a) before sublimation coating, (b) after sublimation coating of MCA for 3 min, and (c) after subsequent prebaking at 110 °C for 2 min. Insets show POM photographs between crossed polarizers.
similar depth upon prebaking, regardless of the differences in the initial polymer film thickness. 3.2. Axis-Selective Photoreaction on Irradiation of MCA-Coated P6BAM Films. Axis-selective photoreaction was observed when a P6BAM film coated with MCA (3 min sublimation) was irradiated with LP 313 nm light, even though the P6BAM film itself is photoinactive. After irradiation, the resultant optical anisotropy of MCA was then able to drive molecular reorientation of P6BAM when subsequently annealing within its LC temperature range. Figure 6a shows Figure 4. Changes in UV absorption spectra of MCA-coated P6BAM films after dipping in n-butanol: (a) without prebaking, and (b) prebaked film (110 °C/2 min) and dipped for 24 h.
dissolution of the MCA. In contrast, a film prebaked at 110 °C did not show any changes when immersed in the same solvent (Figure 4b). In comparison, a prebaked P6BAM/MCA (8/2 wt/wt) composite film showed a slight change after n-butanol treatment, while the MCA molecules in a MCA/PMMA (poly(methyl methacrylate)) composite film were found to completely dissolve (Figure S2a and b). These results indicate that the MCA molecules in P6BAM are bound strongly enough to the matrix through H-bonding to withstand dissolution, in contrast to a discrete MCA layer on top of a polymeric film, or the case where MCA is bound to a polymer matrix but is unable to H-bond due to lack of appropriate side groups. Figure 5 shows UV−vis absorption spectra of MCA-coated P6BAM films after prebaking, with variations in the initial P6BAM thickness. In all cases, MCA was sublimation-coated at 200 °C for 3 min, and subsequently prebaked at 110 °C for 2 min. The absorbance of MCA is similar, indicating that the coated MCA molecules penetrated into the P6BAM film with a
Figure 6. Changes in the polarized UV−vis absorption spectra of (a) the P6BAM film (200 nm thick) coated with MCA (3 min sublimation) without prebaking, and (b) after prebaking at 110 °C for 2 min. The light blue line was acquired before irradiation with LP 313 nm light for 0.5 J/cm2, and the dark blue lines after; the red lines were acquired after subsequent annealing at 170 °C for 10 min.
the changes in the polarized UV−vis absorption spectra of a MCA-coated P6BAM film (without prebaking) before and after irradiation with LP 313 nm light for 0.5 J/cm2, and after annealing at 170 °C for 10 min. A small photoinduced negative optical anisotropy (A∥ − A⊥ < 0) was observed at 320 nm after photoexposure, arising from axis-selective photoreaction of MCA; after annealing, the absorbance of the BA side groups parallel to E suggests that the thermal treatment induced anisotropy in P6BAM (DR = 0.23 at 262 nm), and the absorption bands of MCA were simultaneously seen to disappear. It is thought that the axis-selectively photoreacted MCA molecules in contact with P6BAM influence the molecular motion of the BA side groups during annealing at 170 °C, where the partial penetration upon annealing occurs to affect the anisotropic motion of the film. Simultaneously, the annealing led to sublimation of the MCA molecules, such that the film’s surface became somewhat smooth (Sa = 1.95 nm, Figure S3a).
Figure 5. UV−vis absorption spectra of P6BAM films with various thickness coated with MCA (3 min sublimation), and subsequently prebaked at 110 °C for 2 min. C
DOI: 10.1021/acs.langmuir.7b00079 Langmuir XXXX, XXX, XXX−XXX
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Langmuir In contrast, the thermally induced molecular reorientation of P6BAM was much more significant when using a prebaked film as shown in Figure 6b. In this case, the photoinduced optical anisotropy observed in the MCA absorption was similar to that for the unbaked film, but the subsequent annealing stage significantly increased the absorbance of the BA absorption band perpendicular to E, while decreasing the parallel absorbance. The thermally amplified DR value was estimated to be 0.47 at 262 nm, which is similar to values calculated in a previous study, investigating the photoinduced orientation of a P6BAM/MCA (9/1 wt/wt) composite film after annealing.32 The axis-selective photoreaction of MCA in the P6BAM film effectively generated the molecular reorientation of BA side groups on the thermal stimulation due to the formation of Hbonds between BA and MCA groups in the film. Additionally, the reoriented film’s surface was recorded to possess roughness similar to that before exposure (Sa ≈ 1.0 nm, Figure S3b), indicating that the reorientation process, which proceeds with simultaneous elimination of MCA molecules, does not affect the flatness of the film surface. 3.3. Influence of Sublimation Time, Exposure Energy, and Film Thickness on the Reorientation Behavior. Figure 7a plots thermally amplified, photoinduced DR values of
Figure 8. Thermally amplified photoinduced retardation and birefringence of P6BAM films as functions of film thickness. For all films, MCA was sublimed for 3 min followed by prebaking at 110 °C for 2 min. The films then were irradiated with LP 313 nm light for 0.5 J/cm2 and subsequently annealed at 170 °C for 10 min.
MCA did not change significantly with P6BAM thickness. These results could suggest that the thermally stimulated reorientation of BA side groups in the upper regions of the film (i.e., closer to the free surface), where the H-bonds between MCA and BA form, can partially propagate, leading to knockon reorientation of some of the BA side groups in the lower regions of the film (where MCA does not penetrate). Seki et al. reported that the photoinduced reorientation of top-coated azobenzene-containing polymer also stimulated the molecular reorientation of the inner side of the photoinactive LCP film.37,38 At present, however, the cross-sectional molecular structure of the reoriented P6BAM film has not been determined to assess whether this is the case in this study. 3.4. Patterned Orientation Using Inkjet Coating. Patterned orientation of P6BAM films was demonstrated by inkjet coating the MCA layer (Figure 9) onto the polymer.
Figure 7. (a) Thermally amplified photoinduced DR values of 200 nm thick P6BAM films (a) as a function of MCA sublimation coating time (exposure energy was 0.5 J/cm2), and (b) DR and degree of MCA photoreaction MCA as a function of exposure energy (sublimation coating time was 3 min). All films were annealed at 170 °C for 10 min after LP light exposure.
200 nm thick P6BAM films as a function of MCA sublimation time. For films without prebaking, the generated DR was estimated to be lower than 0.23, thought to be due to the less degree of interaction between photoreacted MCA and BA side groups in the film, as well as the fact that the excess MCA on the film does not contribute to thermal amplification of the reorientation process. In contrast, larger DR values (>0.4) were obtained for the prebaked films, which we attribute to the formation of H-bonds between axis-selectively photoreacted MCA and the BA side groups, which effectively amplified the thermally stimulated reorientation. Figure 7b plots thermally stimulated DR values, and degree of MCA photoreaction for 200 nm thick P6BAM films coated with MCA (3 min sublimation and prebaking at 110 °C) as a function of exposure energy. Significant thermally induced amplification of the photoinduced optical anisotropy was detected when the degree of MCA photoreaction was approximately 35%, similar to that observed in P6BAM/MCA (9/1 wt/wt) composite films reported in a previous study.32 Increases in P6BAM thickness were accompanied by increases in thermally stimulated retardation values, from 22.5 nm (200 nm thickness) to 33 nm (500 nm thickness) as plotted in Figure 8, even though the total amount of penetrated
Figure 9. POM photographs of patterned and oriented P6BAM films between crossed polarizers. MCA molecules were coated by inkjet from DMSO solution. The birefringent pattern was set by irradiating with LP 313 nm light for 0.5 J/cm2, followed by annealing at 170 °C. White arrows indicate the polarizer and analyzer directions, while the blue arrows indicate polarization (E) of LP 313 nm light. (a) Initial P6BAM film; (b) first pattern formation; (c) pattern erasure by annealing at 180 °C; (d) second pattern formation; (e) second erasure by annealing at 180 °C; and (f) third pattern formation.
First, MCA was coated from a DMSO solution onto the P6BAM films by inkjet. The MCA layer was not seen to form crystals after coating, as was the case for sublimation: this is attributed to partial dissolution of the film upon inkjetting. Birefringence was not observed, either after coating or after prebaking at 110 °C, due to the penetration of MCA molecules into the P6BAM film. Thereafter, the film was exposed to LP D
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Figure 10. POM photographs of multipattern oriented P6BAM films between crossed polarizers. MCA molecules were coated by inkjet from DMSO solution. White arrows indicate the polarizer and analyzer directions, while the blue arrows indicate polarization (E) of LP 313 nm light. (a) First inkjet coating of MCA (aromatic ring shape); (b) after irradiation with LP 313 nm light for 0.5 J/cm2 and subsequent annealing at 170 °C for 10 min; (c) second inkjet coating of MCA (“1st” shape); and (d) after irradiation with LP 313 nm light for 0.5 J/cm2 with a changed polarization angle of 45°, and subsequent annealing at 170 °C for 10 min.
313 nm light for 0.5 J/cm2, followed by annealing at 170 °C for 10 min: this process led the formation of a birefringent pattern caused by molecular reorientation in the MCA-coated region (Figure 9a,b), and the recorded birefringent pattern exhibited durability to 313 nm UV light, as evidenced by the lack of an absorption band at this wavelength in the oriented film (Figure S4). Interestingly, the reoriented structure can be erased as demonstrated in Figure 9c: this was achieved by annealing the film at 180 °C, the isotropic temperature of P6BAM, and recoating the erased film with MCA; subsequent application of the same procedure led to a reformation of the patterned and reoriented molecular structure (Figure 9d−f). This behavior is explained by the random orientation assumed by BA side groups during annealing at the isotropic temperature, thereby allowing repeated creation of the birefringent pattern on the P6BAM film. Furthermore, by inkjet coating multiple layers of MCA, multiple oriented patterns with different orientation directions can be realized, as shown in Figure 10a−d. After the first birefringent pattern was recorded (Figure 10b), the second MCA pattern was applied to the film in a nonpatterned area (Figure 10c). The film was then exposed to LP 313 nm light while changing the polarization angle to 45°, and subsequently annealed at 170 °C. As shown in Figure 10d, this demonstrates the successful fabrication of birefringent patterns corresponding to the first and second inkjet coatings with different orientation directions. Because the BA side groups do not absorb 313 nm light, the BA side groups oriented in the first alignment process were not affected by the second exposure, resulting in the multiple alignment directions of the BA side groups.
alignment directions were created by stepwise photoinduced orientation of the MCA-coated region. This technique offers a route to new functional birefringent devices with multiple orientation directions.
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ASSOCIATED CONTENT
* Supporting Information S
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.langmuir.7b00079. Figures showing changes in the thickness after prebaking of MCA-coated films as a function of initial film thickness, changes in UV absorption spectra of P6BAM/MCA (8/2 wt/wt) and PMMA/MCA (8/2 wt/wt) composite films after dipping in n-butanol, threedimensional image of the surface topology of the reoriented films, POM photographs of a patterned oriented P6BAM film before and after irradiation with nonpolarized (NP) UV 313 nm light, and UV-durability of a reoriented P6BAM (PDF)
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Nobuhiro Kawatsuki: 0000-0003-3276-1552 Notes
The authors declare no competing financial interest.
■ ■
ACKNOWLEDGMENTS This work was partially supported by Grants-in-Aid for Scientific Research from JSPS (B15H03869 and S16H06355).
4. CONCLUSION Molecularly oriented films of photoinactive P6BAM were fabricated by top-coating with MCA, irradiating with LP 313 nm light, and a final annealing stage. Prebaking the MCAcoated P6BAM films drove the formation of H-bonds between MCA and BA side groups, and planarizes the film’s surface after sublimation coating of MCA. The axis-selective photoreaction of MCA combined with the subsequent annealing step stimulates molecular reorientation of the BA side groups in P6BAM, alongside simultaneous elimination of MCA molecules, similar to behaviors previously observed in P6BAM/ MCA composite films. Because MCA molecules can be easily coated on the P6BAM film by inkjet, simple fabrication of patterned and oriented P6BAM films was achieved, and the birefringent pattern was shown to be thermally erasable and rerecordable. Additionally, multiple patterns with controlled
REFERENCES
(1) Schadt, M.; Schmitt, K.; Kozinkov, V.; Chigrinov, V. Surfaceinduced parallel alignment of liquid crystals by linearly polymerized photopolymers. Jpn. J. Appl. Phys. 1992, 31, 2155−2164. (2) Schadt, M.; Seiberle, H.; Schuster, A. Optical patterning of multidomain liquid-crystal displays with wide viewing angles. Nature 1996, 381, 212−215. (3) W. M. Gibbons, W. M.; Shannon, V.; Sun, S. T.; Swetlin, B. J. Surface-mediated alignment of nematic liquid crystals with polarized laser light. Nature 1991, 351, 49−50. (4) Chigrinov, V. G.; Kozenkov, V. M.; Kwok, H.-S. Photoalignment of Liquid Crystalline Materials; John Wiley & Sons: West Sussex, England, 2008. E
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Langmuir (5) Kawatsuki, N.; Ono, H. Photoinduced Reorientation of PhotoCross-Linkable Polymer Liquid Crystals and Applications to Highly Functionalized Optical Devices. In Organic Electronics and Photonics; Nalwa, H. S., Ed.; American Sci. Publishers: Stevenson Ranch, CA, 2008; Vol. 2, pp 301−344. (6) Häckel, M.; Kador, L.; Kropp, D.; Schmidt, H.-W. Polymer Blends with Azobenzene- Containing Block Copolymers as Stable Rewritable Volume Holographic Media. Adv. Mater. 2007, 19, 227− 231. (7) Shishido, A. Rewritable holograms based on azobenzenecontaining liquid-crystalline polymers. Polym. J. 2010, 42, 525−533. (8) Yaroshchuk, O.; Reznikov, Y. Photoalignment of liquid crystals: basics and current trends. J. Mater. Chem. 2012, 22, 286−300. (9) O’Neill, M.; Kelly, S. M. Photoinduced surface alignment for liquid crystal displays. J. Phys. D: Appl. Phys. 2000, 33, R67−R84. (10) Wilderbeek, H.-T.-A.; Teunissen, J.-P.; Bastiaansen, C. W. M.; Broer, D. J. Patterned Alignment of Liquid Crystals on Selectively Thiol-Functionalized Photo-Orientation Layers. Adv. Mater. 2003, 15, 985−988. (11) Ryabchum, A.; Bobrovsky, A.; Chun, S.-H.; Shibaev, V. A novel generation of photoactive comb-shaped polyamides for the photoalignment of liquid crystals. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4031−4041. (12) Seki, T.; Nagano, S.; Hara, M. Versatility of photoalignment techniques: From nematics to a wide range of functional materials. Polymer 2013, 54, 6053−6072. (13) Ichimura, K. Photoalignment of Liquid-Crystal Systems. Chem. Rev. 2000, 100, 1847−1874. (14) Ikeda, T. Photomodulation of liquid crystal orientations for photonic applications. J. Mater. Chem. 2003, 13, 2037−2057. (15) Seki, T. New strategies and implications for the photoalignment of liquid crystalline polymers. Polym. J. 2014, 46, 751−768. (16) Natansohn, A.; Rochon, P. Photoinduced Motions in AzoContaining Polymers. Chem. Rev. 2002, 102, 4139−4175. (17) Cipparrone, G.; Pagliusi, P.; Provenzano, C.; Shibaev, V. P. Reversible Photoinduced Chiral Structure in Amorphous Polymer for Light Polarization Control. Macromolecules 2008, 41, 5992−5996. (18) Date, R. W.; Fawcett, A. H.; Geue, T.; Haferkorn, J.; Malcolm, R. K.; Stumpe, J. Self-Ordering within Thin Films of Poly(olefin sulfone)s. Macromolecules 1998, 31, 4935−4949. (19) Kawatsuki, N.; Goto, K.; Kawakami, T.; Yamamoto, T. Reversion of Alignment Direction in the Thermally Enhanced Photoorientation of Photo-Cross-Linkable Polymer Liquid Crystal Films. Macromolecules 2002, 35, 706−713. (20) Kawatsuki, N. Photoalignment and Photoinduced Molecular Reorientation of Photosensitive Materials. Chem. Lett. 2011, 40, 548− 554. (21) Kawatsuki, N.; Kawanishi, T.; Uchida, E. Photoinduced Cooperative Reorientation in Photoreactive Hydrogen-Bonded Copolymer Films and LC Alignment Using the Resultant Films. Macromolecules 2008, 41, 4642−4650. (22) Kato, T.; Fréchet, J. M. A new approach to mesophase stabilization through hydrogen bonding molecular interactions in binary mixtures. J. Am. Chem. Soc. 1989, 111, 8533−8534. (23) Kosaka, Y.; Kato, T.; Uryu, T. Synthesis and the Smectic Mesophase of Copolymers Containing a Mesogenic (Carbazolylmethy1ene)aniline Group as the Electron Donor and a (4′-Nitrobenzy1idene)aniline Group as the Electron Acceptor. Macromolecules 1994, 27, 2658−2663. (24) Kato, T.; Mizoshita, N.; Kishimoto, K. Functional LiquidCrystalline Assemblies: Self-Organized Soft Materials. Angew. Chem., Int. Ed. 2006, 45, 38−68. (25) Kato, T.; Hirota, N.; Fujishima, A.; Fréchet, J. M. J. Supramolecular hydrogen-bonded liquid−crystalline polymer complexes. Design of side-chain polymers and a host−guest system by noncovalent interaction. J. Polym. Sci., Part A: Polym. Chem. 1996, 34, 57−62. (26) Medvedev, A. V.; Baramatov, E. B.; Medvedev, A. S.; Shibaev, V. P.; Ivanov, S. A.; Kozlovsky, M.; Stumpe, J. Phase Behavior and
Photooptical Properties of Liquid Crystalline Functionalized Copolymers with Low-Molecular-Mass Dopants Stabilized by Hydrogen Bonds. Macromolecules 2005, 38, 2223−2229. (27) Millaruelo, M.; Chinelatto, L. S.; Oriol, L.; Pinol, M.; Serrano, J.; Tejedor, R. M. Synthesis and Characterization of Supramolecular Polymeric Materials Containing Azopyridine Units. Macromol. Chem. Phys. 2006, 207, 2112−2120. (28) Koskela, J. E.; Vapaavuori, J.; Hautala, J.; Priimagi, A.; Faul, C. F. J.; Kaivola, M.; Ras, R. H. A. Surface-Relief Gratings and Stable Birefringence Inscribed Using Light of Broad Spectral Range in Supramolecular Polymer-Bisazobenzene Complexes. J. Phys. Chem. C 2012, 116, 2363−2370. (29) Zettsu, N.; Ogasawara, T.; Mizoshita, N.; Nagano, S.; Seki, T. Photo-Triggered Surface Relief Grating Formation in Supramolecular Liquid Crystalline Polymer Systems with Detachable Azobenzene Unit. Adv. Mater. 2008, 20, 516−521. (30) Zhang, Q.; Wang, X.; Barrett, C. J.; Bazuin, C. G. Spacer-Free Ionic Dye−Polyelectrolyte Complexes: Influence of Molecular Structure on Liquid Crystal Order and Photoinduced Motion. Chem. Mater. 2009, 21, 3216−3227. (31) Priimagi, A.; Saccone, M.; Cavallo, G.; Shishido, A.; Pilati, T.; Metrangolo, P.; Resnati, G. Photoalignment and Surface-ReliefGrating Formation are Efficiently Combined in Low-MolecularWeight Halogen-Bonded Complexes. Adv. Mater. 2012, 24, OP345− OP352. (32) Minami, S.; Kondo, M.; Kawatsuki, N. Fabrication of UVinactive photoaligned films by photoinduced orientation of H-bonded composites of non-photoreactive polymer and cinnamate derivative. Polym. J. 2016, 48, 267−271. (33) Fujii, R.; Kondo, M.; Kawatsuki, N. Photoinduced Orientation of a Photoinactive Liquid Crystalline Polymer Doped with NBenzylideneaniline Derivatives. Chem. Lett. 2016, 45, 673−675. (34) Nagano, S. Inducing Planar Orientation in Side-Chain LiquidCrystalline Polymer Systems via Interfacial Control. Chem. Rec. 2016, 16, 378−392. (35) Seki, T. J. Light-directed alignment, surface morphing and related processes: recent trends. J. Mater. Chem. C 2016, 4, 7895− 7910. (36) Fukuhara, K.; Fujii, Y.; Nagashima, Y.; Hara, M.; Nagano, S.; Seki, T. Liquid-Crystalline Polymer and Block Copolymer Domain Alignment Controlled by Free-Surface Segregation. Angew. Chem., Int. Ed. 2013, 52, 5988−5991. (37) Fukuhara, K.; Nagano, S.; Hara, M.; Seki, T. Free-surface molecular command systems for photoalignment of liquid crystalline materials. Nat. Commun. 2014, 5, 3320. (38) Nakai, T.; Tanaka, D.; Hara, M.; Nagano, S.; Seki, T. Free Surface Command Layer for Photoswitchable Out-of-Plane Alignment Control in Liquid Crystalline Polymer Films. Langmuir 2016, 32, 909−914. (39) Takeshima, T.; Kiao, W.; Nagashima, Y.; Beppu, K.; Hara, M.; Nagano, S.; Seki, T. Photoresponsive Surface Wrinkle Morphologies in Liquid Crystalline Polymer Films. Macromolecules 2015, 48, 6378− 6384. (40) Kawatsuki, N.; Miyake, K.; Kondo, M. Facile Fabrication, Photoinduced Orientation, and Birefringent Pattern Control of Photoalignable Films Comprised of N-Benzylideneaniline Side Groups. ACS Macro Lett. 2015, 4, 764−768. (41) Miyake, K.; Ikoma, H.; Okada, M.; Matsui, S.; Kondo, M.; Kawatsuki, N. Orientation Direction Control in Liquid Crystalline Photoalignable Polymeric Films by Adjusting the Free-Surface Condition. ACS Macro Lett. 2016, 5, 761−765.
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DOI: 10.1021/acs.langmuir.7b00079 Langmuir XXXX, XXX, XXX−XXX
