Optically and spatially templated polymer architectures formed by photopolymerization of reactive mesogens in periodically deformed liquid crystals

• Published in: NPG Asia materials 2017-08, Vol.9 (8), p.e429-e429
• Main Authors: Baliyan, Vijay Kumar, Lee, Seung Hee, Kang, Shin-Woong
• Format: Article
• Language: English
• Subjects: 119/118; 639/301/923/1028; 639/301/923/919; 639/624/399/1028; 639/624/399/919; 639/638/298/919; Biomaterials; Birefringence; Chemistry and Materials Science; Elastic deformation; Electric fields; Electrodes; Energy Systems; Forming; Liquid crystals; Materials Science; Nematic; Networks; Optical and Electronic Materials; original-article; Photopolymerization; Polymerization; Polymers; Solvents; Spatial distribution; Structural Materials; Surface and Interface Science; Template matching; Thin Films
• ISSN: 1884-4049; 1884-4057
• DOI: 10.1038/am.2017.151

A unique and versatile method for forming optically (that is, orientationally) and spatially patterned polymer architectures was developed based on the photopolymerization of reactive mesogens (RMs) in a periodically deformed liquid crystal (LC). Without using lithographic or holographic implements, various polymer patterns were produced by employing nematic LCs as reaction solvents and spatially nonuniform electric fields. The nematic mixture, containing 5.0 wt.% RMs and sandwiched between patterned electrodes, was exposed to spatially uniform reaction-initiating radiation. The spatially nonuniform electric field induced periodic optical patterns in the reaction template with spatially varying elastic deformations. The resulting polymerized RM networks were both spatially and optically patterned, with good fidelity with respect to the electrode pattern and subsequent periodic director profiles. The spatial distribution of dense RM networks coincided precisely with the profile of highly deformed regions in the reaction medium. The optical birefringence of the polymer network was templated by the local director of the reaction template. Numerical calculations of director configuration and the associated elastic energy of the reaction template precisely matched the spatial and orientational order of polymerized RM networks. The proposed method provides ease and flexibility in forming organized polymer architectures for functional materials that require both positional and orientational order for their applications. Liquid crystals: A new angle on building 3D polymers Using pre-aligned liquid-crystal templates, scientists have developed a versatile way to pattern polymers into optically active orientations. The approach from Shin-Woong Kang and co-workers at Chonbuk National University in Korea involves dissolving a small amount of a photoreactive monomer in a nematic liquid-crystal solvent. After sandwiching the mixture inside a glass case, the team controlled spatially varying elastic deformation of the solvent and exposed the cell to ultraviolet light. This procedure photopolymerized the monomer into three-dimensional polymers with network structures highly sensitive to the liquid-crystal solvent. Inspired by simulations that showed how elastic deformations drive this type of templating, the researchers applied spatially non-uniform electric fields in forming LC-templates. This induced periodic patterns that could embed optical birefringence into the polym