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Applications of Polymer, Composite, and Coating Materials
Non-electric sustaining bistable polymer framework liquid crystal films with novel semi-rigid polymer matrix Wei Hu, Mei Chen, Le Zhou, Tingjun Zhong, Xiaotao Yuan, Feiwu Chen, and Lanying Zhang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b06324 • Publication Date (Web): 12 Jun 2018 Downloaded from http://pubs.acs.org on June 13, 2018
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ACS Applied Materials & Interfaces
Non-electric sustaining bistable polymer framework liquid crystal films with novel semi-rigid polymer matrix Wei Hu,a Mei Chen,b Le Zhou,b Tingjun Zhong,b Xiaotao Yuan,a* Feiwu Chena* and Lanying Zhangb* a
Department of Chemistry and Chemical Engineering, School of Chemistry and
Biological Engineering, University of Science and Technology Beijing, Beijing 100083, People’s Republic of China b
Department of Materials Science and Engineering, College of Engineering, Peking
University, Beijing 100871, People's Republic of China Keywords: bistable, polymer framework liquid crystal, rigid-structure thiol, thermal curing, energy-efficient
Abstract: In this work, a bistable polymer framework liquid crystal (PFLC) thin film by thermal curing of epoxy monomers with two different thiols, a traditional flexible-structure thiol and a novel original rigid-structure thiol has been successfully fabricated, combining a novel mixed morphology of polymer matrix and cholesteric liquid crystals with negative dielectric anisotropy. The polymer framework morphology has been presented by curing two types of epoxy monomers with two types of thiols, and the liquid crystals tend to be focal conic textures with large size domains at the initial state in the PFLC film, so that it has a moderate light transmissivity at this state between the transparent state and the opaque state. Thus, the devices based on PFLC films can be switched reversibly between transparent state
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and opaque state by alternative electric field. In addition, the states can be sustained after the electric field is removed. The bistable memory effect comes from the anchoring effects of the polymer frameworks with novel morphology in the microdomains of the PFLCs. Therefore, the optimized bistable PFLC film keep its initial state without external electric field and any other energy consumption for a long time after altering state by applying an instant electric field. The special polymer frameworks in the bistable PFLC films endow the films with excellent electro-optical properties and mechanical properties. The devices are energy-efficient and cost-saving and have great potential applications in energy-efficient reflective displays, electronic papers, writing tablets, and smart windows. 1. Introduction The electro-optic properties of liquid crystals (LCs) and polymer composites have been employed to make large and flexible displays, optical shutters and switchable windows.1-5 Polymer dispersed liquid crystals (PDLCs) and polymer stabilized liquid crystals (PSLCs) are known as classical technologies for fabrication of these types of devices.6-7 In PDLCs, the micron size droplets of liquid crystals are dispersed in isotropic polymers.8-18 At the initial state, the materials are opaque (optical scattering), for the liquid crystals are randomly oriented throughout the system so that the refractive indices between the liquid crystal and polymer matrix are mismatched. The scattering intensity of the composites reduced until to be transparent with decrease of the refractive index difference between LCs and polymers, by applied an appropriate voltage pulses to adjust the alignment of LC droplets. The
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ACS Applied Materials & Interfaces
anchoring effects between isotropic polymers and rigid liquid crystals in PDLCs are very weak, so the traditional switchable smart window needs to be placed in a sustained electric field to maintain its state after switching the opaque state to the transparent state by applied voltage pulses.19-23 Although many researches have been focused on reducing its driving voltage, which has been decreased to below safe voltage, strictly speaking, PDLC film is still not an absolute energy-saving product.24-26 Therefore, a more energy-efficient approach is urgently needed. Deng-Ke Yang et al. have developed a bistable polymer stabilized cholesteric texture (PSCT) light shutter which can be switched between a transparent state and an opaque state by applied voltage pulses.27 The PSCT light shutter is switched to a transparent state by applying a low frequency (LF) voltage pulse and to an opaque state while a high frequency (HF) voltage pulse is applied, then it remains at the state after removing the pulse. In PSCT, the cholesteric texture is stabilized by polymer networks,27-31 and the crosslinked rigid polymers, usually in a small amount (
