Molecular Simulation of the Free Surface Order in NLC Samples

The orientation of liquid crystal molecules is very sensitive towards contacting surfaces, and this phenomenon is critical during the fabrication of liquid crystal display panels, as well as optical and memory devices. To date, research has focused on designing and modifying solid surfaces. Here we report an approach to control the orientation of liquid crystals from the free (air) surface side: a skin layer at the free surface was prepared using a non-photoresponsive liquid crystalline polymer film by surface segregation or inkjet printing an azobenzene-containing liquid crystalline block copolymer. Both planar-planar and homoeotropic-planar mode patterns were readily generated. This strategy is applicable to various substrate systems, including inorganic substrates and flexible polymer films. These versatile processes require no modification of the substrate surface and are therefore expected to provide new opportunities for the fabrication of optical and mechanical devices based on liquid crystal alignment.

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“…3g. These results agree with the general understanding that rod-like mesogenic groups tend to be anchored vertically at the free surface17181920.…”

Section: Resultssupporting

confidence: 91%

Free-surface molecular command systems for photoalignment of liquid crystalline materials

et al. 2014

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“…One approach to achieve alignment of LC BCPs is to control the orientation of calamitic LC mesogens at the substrate and the free surface . The LC mesogens display homeotropic behavior and form layered structures because of surface effects and LC anchoring . In thin films of LC BCP with a free surface, the anchoring of the LC mesogens at the interface with air promotes perpendicular alignment of the microphase‐separated domains to the substrate surface after thermal annealing .…”

Section: Introductionmentioning

confidence: 99%

Water‐soluble top coats for orientation control of liquid crystal‐containing block copolymer films

Xie

Suh

et al. 2017

J Polym Sci B Polym Phys

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An easily removable, water-soluble top coat of polyvinylpyrrolidone (PVP) is used to control the orientation of microdomains in a liquid crystalline block copolymer (LC BCP, poly(ethylene oxide)-block-poly(6-(4-methoxy-azobenzene-4 0butyl) hexyl methacrylate)). The corresponding LC homopolymer is also investigated for comparison. Atomic force microscopy is used to determine the orientation of the cylindrical microdomains of the LC BCP. UV-vis spectroscopy and grazing incidence wide-angle X-ray scattering are used to determine the orientation of the LC mesogens in the LC homopolymer and the LC BCP films annealed both with and without a top coat. Once the LC BCP morphology is self-assembled, the PVP top coat layer can be easily removed with water or alcohol. The facile removal of the top coat improves the processability of BCPs in technological applications, and enables direct investigation of the BCP morphology in scientific studies.

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“…The homeotropic surface anchoring effect and layer structuring at the free surface of calamitic LC molecules have been shown experimentally [10] and have been further verified by theoretical simulations. [11] To modify the free surface, the present approach adopts the surface segregation [12,13] of a small amount of a free-surface-active polymer. We demonstrate here that the coverage of the surface with the free-surface-active polymer leads to a homeotropic-to-parallel orientation change of LC mesogens, which further leads to an efficient in-plane photoalignment of microphase separation (MPS) domains of a relevant LC block copolymer by linearly polarized light (LPL).…”

mentioning

confidence: 99%

Liquid‐Crystalline Polymer and Block Copolymer Domain Alignment Controlled by Free‐Surface Segregation

et al. 2013

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The surface effects and anchoring of liquid crystals (LCs) have long been significant concerns for material chemists and physicists.[1] The surface alignment of LCs by mechanical rubbing [2] is a widely recognized phenomenon and of particular significance in technological applications for display device fabrication.[3] Surface molecular orientations [4] and topographical grooves and undulations [5] of the substrate provide LC alignment effects. Furthermore, in the past two decades, the photoalignment of LCs on photoreactive polymer film surfaces by anisotropic irradiation [6] has become a significant method and an alternative to mechanical rubbing processes. The aligning substrates are not limited to polymer surfaces; various types of surfaces, such as hard inorganic materials [7] and soft bio-related interfaces, [8] can be used for the alignment induction. In addition to low-molecular-mass LCs, polymer LC materials are also aligned by the surface effect.[9] Despite the tremendous amount of accumulated knowledge and the number of potential applications, the surface alignment processes developed to date mostly involve manipulations on the surfaces of solid or condensed phases.Herein, we report on LC alignment alternation, which is attained by a modification of the free surface (air-film interface). The homeotropic surface anchoring effect and layer structuring at the free surface of calamitic LC molecules have been shown experimentally [10] and have been further verified by theoretical simulations.[11] To modify the free surface, the present approach adopts the surface segregation [12,13] of a small amount of a free-surface-active polymer. We demonstrate here that the coverage of the surface with the free-surface-active polymer leads to a homeotropic-to-parallel orientation change of LC mesogens, which further leads to an efficient in-plane photoalignment of microphase separation (MPS) domains of a relevant LC block copolymer by linearly polarized light (LPL).[14] With regard to the MPS alignment control, the important role of a top coat layer has recently been demonstrated by Bates et al. [15] In this case, a polar-to-nonpolar chemical conversion of the top layer is achieved to fulfill the requirement of spin-casting from an aqueous solvent and to provide a neutral (non-preferential) layer for the hydrophobic block copolymer during the annealing. In the present approach, in contrast, no additional coating procedure is required, providing a simple, versatile method for the desired alignment control of MPS domains.First, the alignment behavior of an LC azobenzene (Az) homopolymer (PAz in Figure 1 a; M n = 8.0 10 4 , M w /M n = 1.13, and g-43 8C-SmC-100 8C-SmA-120 8C-iso) was examined. A spincast film of PAz was prepared (thickness: 100-200 nm) from a chloroform solution. After annealing at 130 8C (above the isotropization temperature) for 10 min followed by gradual cooling via a smectic LC phase to room temperature, this film spontaneously formed the out-of-plane (perpendicular) orientation of Az side mesogens, a...

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Molecular Simulation of the Free Surface Order in NLC Samples

Cited by 20 publications

References 14 publications

Free-surface molecular command systems for photoalignment of liquid crystalline materials

Free-surface molecular command systems for photoalignment of liquid crystalline materials

Water‐soluble top coats for orientation control of liquid crystal‐containing block copolymer films

Liquid‐Crystalline Polymer and Block Copolymer Domain Alignment Controlled by Free‐Surface Segregation

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