Orientation Direction Control in Liquid Crystalline Photoalignable Polymeric Films by Adjusting the Free-Surface Condition

Miyake, Kazutoshi; Ikoma, Hiromi; Okada, Makoto; Matsui, Shinji; Kondo, Mizuho; Kawatsuki, Nobuhiro

doi:10.1021/acsmacrolett.6b00252

Cited by 12 publications

(11 citation statements)

References 28 publications

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“…26–28 have also demonstrated the control of mesogen orientation from the free surface using different types of photoreactive unit. The top skin layer can be prepared by surface segregation of a surface active photoresponsive polymer 21,22,25 or local deposition by inkjet printing 22,27,28 .…”

Section: Introductionmentioning

confidence: 99%

Photoinitiated Marangoni flow morphing in a liquid crystalline polymer film directed by super-inkjet printing patterns

Kitamura

Oishi

Hara

et al. 2019

Sci Rep

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Slight contaminations existing in a material lead to substantial defects in applied paint. Herein, we propose a strategy to convert this nuisance to a technologically useful process by using an azobenzene-containing side chain liquid crystalline (SCLCP) polymer. This method allows for a developer-free phototriggered surface fabrication. The mass migration is initiated by UV-light irradiation and directed by super-inkjet printed patterns using another polymer on the SCLCP film surface. UV irradiation results in a liquid crystal-to-isotropic phase transition, and this phase change immediately initiates a mass migration to form crater or trench structures due to the surface tension instability known as Marangoni flow. The transferred volume of the film reaches approximately 440-fold that of the polymer ink, and therefore, the printed ink pattern acts as a latent image towards the amplification of surface morphing. This printing-aided photoprocess for surface inscription is expected to provide a new platform of polymer microfabrication.

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Section: Introductionmentioning

confidence: 99%

Photoinitiated Marangoni flow morphing in a liquid crystalline polymer film directed by super-inkjet printing patterns

Kitamura

Oishi

Hara

et al. 2019

Sci Rep

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“…Conventionally, surface segregation has been used to modify the topmost surface, affecting the wettability and adsorption properties. − The present approaches can control the internal orientation structure of the film from the free surface by a surface-segregation effect. In recent years, the effect of the free surface has been utilized to control the molecular orientation in free-standing films of various molecular systems such as liquid crystalline polymers, − conductive polymers, discotic liquid crystals, and MPS structures . These approaches are anticipated to be developed as a new molecular alignment technique.…”

Section: Introductionmentioning

confidence: 99%

Random Planar Orientation in Liquid-Crystalline Block Copolymers with Azobenzene Side Chains by Surface Segregation

Nagano

2018

Langmuir

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Rodlike liquid-crystalline (LC) mesogens preferentially adopt a homeotropic orientation by excluded volume effects at the free surface in side-chain LC (SCLC) polymer films. The homeotropic orientation is not advantageous for in-plane LC alignment processes. Surface segregation of polymers is the phenomenon in which one component with a low surface free energy covers the surface in a mixture of two or more polymers or a block copolymer film. In SCLC block copolymer films, the surface segregation structure induces a random planar orientation due to the formation of a microphase-separated interface parallel to the substrate via the covering of one of the segregated polymer blocks. This feature article focuses on the unique, random planar orientation induced by the surface segregation of SCLC block copolymer films with the photoresponsive azobenzene (Az) mesogenic group. A transition moment of the Az mesogens is parallel to the molecular long axis, and light irradiation is conducted perpendicular to the film surface in general photoreaction processes. Therefore, the homeotropic molecular orientation in the SCLC polymer systems with Az mesogenic units inhibits efficient photoreaction reorientations in thin films. The random planar orientations by the surface segregation of a coil block in SCLC block polymers provide efficient in-plane photoreorientation and photoswitching with LC hierarchical mesostructures, such as microphase-separated structures of SCLC block copolymers and laminated LC polymer films. On the other hand, surface-segregated SCLC blocks form a high-density polymer LC brush layer with a random planar orientation by self-assembly, which exhibits efficient angular selective photoreactions. These approaches using the surface segregation of SCLC block copolymers are expected to offer new concepts for the LC photoalignment process for LC polymer devices.

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“…Such a surface is called the command layer 45,52,63 . Recent investigations have revealed that a photoactive command layer can be placed at the free surface in SCLCP films [41][42][43][44][45][46][47] . Similarly, the present work offers another command layer scenario where large www.nature.com/scientificreports/ molecular amplification is reflected in macroscopic surface morphing.…”

Section: Resultsmentioning

confidence: 99%

“…Related to the molecular orientation in SCLCP films, an Az-containing command layer at the free surface or inkjet-printed patterns could control the orientation of the majority of the mesogens of the base film [41][42][43][44][45] . Kawatsuki et al 46,47 also controlled of mesogen orientation from free surfaces using different types of photoreactive units.…”

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confidence: 99%

Photo-triggered large mass transport driven only by a photoresponsive surface skin layer

Kitamura

Kato

Berk

et al. 2020

Sci Rep

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Since the discovery 25 years ago, many investigations have reported light-induced macroscopic mass migration of azobenzene-containing polymer films. Various mechanisms have been proposed to account for these motions. This study explores light-inert side chain liquid crystalline polymer (SCLCP) films with a photoresponsive polymer only at the free surface and reports the key effects of the topmost surface to generate surface relief gratings (SRGs) for SCLCP films. The top-coating with an azobenzene-containing SCLCP is achieved by the Langmuir-Schaefer (LS) method or surface segregation. A negligible amount of the photoresponsive skin layer can induce large SRGs upon patterned UV light irradiation. Conversely, the motion of the SRG-forming azobenzene SCLCP is impeded by the existence of a LS monolayer of the octadecyl side chain polymer on the top. These results are well understood by considering the Marangoni flow driven by the surface tension instability. This approach should pave the way toward in-situ inscription of the surface topography for light-inert materials and eliminate the strong light absorption of azobenzene, which is a drawback in optical device applications. Surface morphology generations on azobenzene(Az)-containing polymer films induced by patterned irradiation have been the active area in photofunctional material research. In 1995, Natansohn's 1 and Tripathy's 2 groups independently reported the induction of surface relief gratings (SRGs) on Az amorphous films using interference irradiation of two laser beams. Since then, photoinduced SRG processes have been reported using various photofunctional materials such as amorphous polymers 1-20 , side chain liquid crystalline polymers (SCLCPs) 21-27 , supramolecular systems 24,27-29 , amorphous molecular materials 30. Additionally, SRG formation can be realised using other photoresponsive units 31-35. Various mechanistic models for mass transfer have been proposed: isomerisation pressure due to volume change 7,8 , gradient force 9-11 , mean-field model 12 , directed softening or fluidisation 13-15 , molecular diffusion 16-18,34 , molecular orientation force 19,20 , etc. With regard to Az-containing SCLCPs 21-27 , UV light irradiation leads to a photochemical phase transition between the liquid crystal (LC) and isotropic phases. This phase change plays an important role in highly efficient SRG formation 23,25,26 , which requires an overall dose of much less than 1 J cm-2. Typically mass transport depends on the light irradiation conditions and physicochemical properties. Consequently, a universal explanation about the mechanism has yet to be provided. Recent studies have noted the importance of the surface effect on the mass transfer process. Ambrosio et al. 17,18 proposed an anisotropic light-driven molecular diffusion model for spiral morphology induction under vortexbeam illumination. Their model stressed enhanced molecular diffusion in proximity of the free surface. Ellison et al. 36-39 have proposed microfabrications via the Marangoni flow by photo...

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Orientation Direction Control in Liquid Crystalline Photoalignable Polymeric Films by Adjusting the Free-Surface Condition

Cited by 12 publications

References 28 publications

Photoinitiated Marangoni flow morphing in a liquid crystalline polymer film directed by super-inkjet printing patterns

Photoinitiated Marangoni flow morphing in a liquid crystalline polymer film directed by super-inkjet printing patterns

Random Planar Orientation in Liquid-Crystalline Block Copolymers with Azobenzene Side Chains by Surface Segregation

Photo-triggered large mass transport driven only by a photoresponsive surface skin layer

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