Effect of cholesteric liquid crystalline elastomer with binaphthalene crosslinkings on thermal and optical properties of a liquid crystal that show smectic A‐cholesteric phase transition

Abstract

A side‐chain polysiloxane cholesteric liquid crystalline elastomer (ChLCE) with binaphthalene derivate as crosslinkings and cholesterol derivate as liquid crystalline monomers was designed and synthesized. A binaphthyl chiral dopant (CD) was synthesized as well. The chemical structures and liquid crystalline properties of the ChLCE and the CD were characterized by Fourier transform infrared spectroscopy, proton nuclear magnetic resonance spectroscopy, element analyses, differential scanning calorimetry and polarizing optical microscopy measurements. The helical twisting power of the ChLCE exhibited a turning point with changing temperature and was smaller than that of the CD. In addition, the effect of the ChLCE on phase transition temperatures and thermal‐optical properties of a liquid crystal that show smectic A (SmA)‐cholesteric (Ch) phase transition was studied. Worthily, the testing of the reflection wavelength with changing temperature suggested that the adding of the ChLCE in liquid crystals that show SmA‐Ch phase transition can expedite their SmA‐Ch transition. In addition, the network structure of the ChLCE may play a significant role in the accelerating of the transition. These properties provided theoretical and experimental foundations for applying ChLCE in thermally sensitive liquid crystal devices requiring fast response, such as thermally controllable windows, materials and displays. Copyright © 2012 John Wiley & Sons, Ltd.

Temperature‐Responsive Photonic Devices Based on Cholesteric Liquid Crystals

“…Free-standing films PSLC with small mesogenic molecules HTP changing [110][111][112][113]115,120] 860À2500 nm, band broadening [110] 0À34 C [110] Complex optical response possible (e.g., band broadening, > 50 % reflection in a single layer) Must be encapsulated Cells 400À700 nm, band shifting [115] 165À190 C [115] SmÀCh transition [116][117][118][119] 300À2500 nm, band broadening [119] 25À132 C [119] Must be encapsulated Cells 750À950 nm, band shifting [117] %20À49 C [117] Reduced wavelength tuning range…”

“…For example, an LC system (8CB/12CB/SLC1717), which has a smectic−nematic phase transition, was blended with a crosslinked polysiloxane elastomer that contained chiral mesogens for inducing the Ch phase, which resulted in a sharp Sm−Ch effect in the cell, even with 25 wt % elastomer fraction. [ 118 ] The material shows a 1200 nm band shift over a temperature change of just 4.8 °C. The assumption is that the elastomeric state of the network enables sufficient reorientation of the mesogens upon temperature variations to accommodate such an extreme transition.…”

Liquid crystal elastomer actuators: Synthesis, alignment, and applications

“…The Finkelmann method was first designed for nematic elastomers; however, this synthetic technique can be applied to other phases, such as cholesteric and smectic phases . Alignment of cholesteric (chiral nematic) LCEs was achieved by Kim and Finkelmann by using a variation of this two‐step hydrosilation reaction route .…”

Liquid Crystal Elastomers—A Path to Biocompatible and Biodegradable 3D-LCE Scaffolds for Tissue Regeneration

“…It describes a two-step crosslinking process, the first being slight crosslinking of LCPs, followed by the orientation of the mesogenic groups; the LCP is then stretched and crosslinked to maintain the orientation [ 26 ]. This technique was also applied to other liquid-crystalline phases (e.g., cholesteric, smectic) [ 41 , 42 , 43 , 44 ]. Other methods have been reported to prepare LCE with different properties, such as reversible crosslinking by a trans-esterification reaction [ 45 ], coupling reactions of thiol-acrylate used for the production of LCEs and aligned by stretching [ 20 ] or by means of patterned surfaces [ 46 ], and a thiolyne coupling reaction developed to produce aligned LCEs using direct light alignment (DLW) surfaces [ 47 ].…”