Comparative Study of Anchoring Strengths for Photo- and Rubbing-Aligned Liquid Crystals on Photoisomerizable Polyimide Alignment Films

Chung, Doo-Han; Takezoe, Hideo; Park, Byoungchoo; Jung, Youngyi; Hwang, Ha-Keun; Lee, Sooman; Han, Ki-Jong; Jang, Sei‐Hum; Yokoyama, Hiroshi

doi:10.1143/jjap.39.1252

Cited by 19 publications

(5 citation statements)

References 20 publications

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“…In that case, the threshold field is expressed as K 22 / ε. The switching field strength of 6.8 V rms µm −1 in this experiment was reasonable considering the previous anchoring strength results of previous studies for the alignment material used in this experiment [26]. With varying field directions, the brightness changed with the switching of the bulk directors and the states that were stable without the field.…”

Section: Resultssupporting

confidence: 88%

Alignment characteristic of nematic liquid crystals on orientational patterns realized by interfering laser light

Lee¹,

Kim²

2008

J. Phys. D: Appl. Phys.

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We have observed the alignment property and switching behaviour of nematic liquid crystals (NLCs) on orientation patterns that were realized on a photo-active alignment layer by using interferring beams of two coherent laser lights. Linearly polarized light orients the liquid crystals in a direction perpendicular to the polarization and the interferring laser light induced a one-dimensional periodic texture following the interference pattern. Using double irradiation, in which the direction of the second irradiation was rotated by 90° to the first irradiation, we constructed a quasi-four-fold symmetric orientation pattern. The NLCs exhibited bistability in two average directions of polarization of the laser light, and they stably switched between the two directions by the in-plane electric field. Furthermore, the NLCs indicated the capability of continuous and memorized switching with a changing electric field on the orientation pattern.

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Section: Resultssupporting

confidence: 88%

Alignment characteristic of nematic liquid crystals on orientational patterns realized by interfering laser light

Lee¹,

Kim²

2008

J. Phys. D: Appl. Phys.

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“…However, we quote the values obtained for another LC, viz., 5CB. Again, the values vary between 0.9 × 10 −4 to 3 × 10 −4 J m −2 , [ 65–67 ] and thus not very different from that for EPD h‐BN. In contrast, cell with EPD h‐BN has ≈30% higher value than that reported for the cell with a CVD‐grown h‐BN layer ( W θ = 2.4 × 10 −4 J m −2 for EPD h‐BN and 1.8 × 10 −4 J m −2 for CVD h‐BN [ 58 ] ).…”

Section: Resultsmentioning

confidence: 99%

Solution‐Processed h‐BN Film as an Alignment Layer for Liquid Crystal Devices: Realization of a Non‐Polymer Approach for Unidirectional Alignment over Unprecedentedly Large Areas

Pisharody

Sahoo

Rao

et al. 2022

Adv Materials Inter

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atomic-scale switches and transistors working at gigahertz frequencies using mechanically cleaved graphene, [3,4] ballistic transport of electrons in graphene-boron nitride heterostructures, [5] ambipolar transport in transition metal dichalcogenides and black phosphorus. [6][7] In contrast to the correlated high thermal and electrical conductivity as in carbon nanotubes or graphene, [8][9] h-BN offers a startlingly different combination of high thermal conductivity and excellent electrical insulation. [10] While the field gained attention with fabrication procedures that are easily realizable, it is the chemical vapor deposition (CVD) technique that truly made the surge ahead, especially because monolayers of large enough dimensions can be obtained. [11][12][13] The importance of aligning liquid crystal (LC) molecules for fabricating a liquid crystal display device needs hardly any emphasis. Indeed, the success mentioned above provided the impetus to employ CVD-grown 2D films as alignment layers for LC molecules. However, it has been realized that the CVD technique suffers from drawbacks such as high operational temperature, need for vacuum, usage of hazardous chemicals, and limited film thickness. [14] Besides, the process is timeconsuming as well as expensive, not to mention the high skills necessary to obtain good quality CVD-grown films. [14] It is with this background that solution processing (SP) of 2D materials, which can address the aforementioned issues in a simple and cost-effective way, is being currently considered as a viable alternative. [15] More importantly, the SP can also offer the possibility of fabricating large-area flexible devices. [16] It may be noted that the SP route has already helped to realize a plethora of devices including capacitors, supercapacitors, transistors, photodetectors, etc. [17][18][19] Despite the simplicity, the performance of the solution-processed electronic devices is reported to be inferior to those obtained by the CVD method. [20][21][22] The compromising device performance being the major hindrance for commercialization of the SP devices, it would be a significant step forward Fabrication of liquid crystal devices heavily relies on the alignment layer providing the mandatory unidirectional orientation of the nematic molecules. Drawbacks of the traditional mechanically rubbed polymer layer have prompted to find better alternatives. However, cost-effective methods for large-area unidirectional alignment are still elusive. The latest attempt has been to use 2D materials deposited through the well-known chemical vapor deposition process, invariably inviting all the associated complexities including high-temperature processing, cumbersome transfer onto the required substrate, etc. Most importantly, the achieved domain size over which the nematic molecules exhibit unidirectional planar orientation, has been too small (sub-mm 2 ) for employable devices. Here, the authors present a room temperature solution process for obtaining h-BN dispersion and directly depositing it...

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“…Photoalignment is primarily categorized into three types in terms of the photoreactions that induce anisotropy. First is photoanisotropy caused by azobenzene 14,21,24,25,31,32,48–61 . Second is photodimerization caused by cinnamate, coumarin, and chalcone 15–17,27,62–81 .…”

Section: Introductionmentioning

confidence: 99%

“…First is photoanisotropy caused by azobenzene. 14,21,24,25,31,32,[48][49][50][51][52][53][54][55][56][57][58][59][60][61] Second is photodimerization caused by cinnamate, coumarin, and chalcone. [15][16][17]27,[62][63][64][65][66][67][68][69][70][71][72][73][74][75][76][77][78][79][80][81] Third is polyimide undergoing photodecomposition.…”

Section: Introductionmentioning

confidence: 99%

Photo‐isomerization, photodimerization, and photodegradation polyimides for a liquid crystal alignment layer

Sugiyama

Sato

Nagai

2022

Polymers for Advanced Techs

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We review the important features of LC orientation for the alignment layer, namely, production method, alignment mechanisms, and required properties. Photoalignment, which could eliminate the disadvantages of the rubbing method is explored. Applicable materials and techniques for photoalignment are also examined. Many materials for photoalignment layers have been proposed, but polyimide‐based materials are commonly used because of their transparency and insulation properties, which are needed for optical electronic devices. Furthermore, photoisomerization, photodimerization, and photodecomposition as photoalignment methods are reviewed, and specific photoreactive groups and alignment mechanisms are used to induce LC alignment. In summary, polyimides cause photodecomposition and have the following disadvantages; (1) requirement of relatively short‐wavelength ultraviolet (UV) irradiation, (2) difficulty in reorienting polymer chains owing to their rigid polymer matrix, and (3) low‐photo reactivities. The solutions for each disadvantage are already proposed, but the required properties should be determined during material design. Polyimide‐based materials introduced with the azobenzene and cinnamate groups are proposed and found to have the ability of fulfilling the required properties. The mechanism of polyimide photodecomposition is not fully understood. It likely has the advantage in terms of LC alignment stability because of the absence of E/Z isomerization. Therefore, the alignment mechanism and availabilities should be further explored.

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Comparative Study of Anchoring Strengths for Photo- and Rubbing-Aligned Liquid Crystals on Photoisomerizable Polyimide Alignment Films

Cited by 19 publications

References 20 publications

Alignment characteristic of nematic liquid crystals on orientational patterns realized by interfering laser light

Alignment characteristic of nematic liquid crystals on orientational patterns realized by interfering laser light

Solution‐Processed h‐BN Film as an Alignment Layer for Liquid Crystal Devices: Realization of a Non‐Polymer Approach for Unidirectional Alignment over Unprecedentedly Large Areas

Photo‐isomerization, photodimerization, and photodegradation polyimides for a liquid crystal alignment layer

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