The influence of the helical twisting power on the bistable electro-optical performance of the liquid crystalline epoxide/mercaptan /negative-dielectric-anisotropy cholesteric liquid crystal composite films

Abstract

Bistable electro-optical devices have been successfully prepared by thermal curing of the liquid crystalline epoxide, mercaptan and the cholesteric liquid crystals (N-ChLCs) with negative-dielectric-anisotropy. In order to study the influence of helical twisting power (HTP), an important parameter of the chiral dopant, on the bistable electro-optical properties of the liquid crystalline epoxide/mercaptan/N-ChLC composite films, four samples A1-A4 were prepared. Among them, four different N-ChLCs with the same Bragg reflect wavelength were prepared via blending the negative dielectric anisotropy nematic liquid crystal and the chiral dopant R811, R1011, R2011, as well as R5011, respectively. Results indicated that as the HTP increased, the transmittance in the wavelength range of 400–2500 nm became lower under the low-frequency (LF) electric field and after removing the LF electric field, which resulted from the smaller polymer microspheres. Meanwhile, samples with large HTP showed their large transmittance states under the high-frequency (HF) electric field (10 KHz, 90V) and after removing the HF electric field. Moreover, the sample A4 possessing the chiral dopant R5011 with a large HTP exhibited good bistability, and its large- and low-transmittance states can be maintained for a long time (>30 days) in the absence of electric fields.