Fabrication and optical characterization of imprinted broad‐band photonic films via multiple gradient UV photopolymerization

• Published in: Journal of polymer science. Part B, Polymer physics Polymer physics, 2017-10, Vol.55 (19), p.1427-1435
• Main Authors: Zhang, Yan‐Song, Emelyanenko, A. V., Liu, Jui‐Hsiang
• Format: Article
• Language: English
• Subjects: Bandwidths; broad‐band Bragg reflection; cholesteric liquid crystal; Cholesteric liquid crystals; imprint; Incident light; Liquid crystals; Luminous intensity; Mesophase; Optical properties; photonic film; Photonics; Photopolymerization; Polymer films; Polymerization; Reflection; Ultraviolet radiation
• ISSN: 0887-6266; 1099-0488
• DOI: 10.1002/polb.24392

ABSTRACT A structured broad‐band photonic film is fabricated by a novel method using multiple gradient UV‐induced polymerization in the presence of cholesteric liquid crystals (CLCs). Here, imprinting and broadening of the reflection band of chiral nematic mesophase cells are achieved via controlled UV polymerization. The intensity gradient of UV light is modified by the distance between UV lamp and sample cell, which affects the polymerization rate and leads to the formation of imprinted helical constructions with different pitches. In this study, a comparison of new design process with traditional UV polymerization process is carried out. After seven cycles of gradient UV polymerization, the imprinted photonic construction exhibited a broadened reflection band and Bragg reflection, even for isotropic materials. Because of this, the reflection bandwidth showed a 70% improvement. Additionally, two stacked imprinted cells with different pitches can reflect incident light with a bandwidth over the visible wavelength range of 480–680 nm. A broad‐band photonic polymer film can be imprinted using multiple gradient UV photopolymerization in the presence of CLCs. Forming a UV intensity gradient and controlling the rate of photopolymerization are key factors in broadening the reflection band. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 1427–1434 A broad‐band photonic polymer film can be imprinted using multiple gradient UV photopolymerization in the presence of cholesteric liquid crystals. Forming a UV intensity gradient and controlling the rate of photopolymerization are key factors in broadening the reflection band.