The role of crosslinking and polarity in the dark relaxation of azobenzene-based, polymer-stabilised cholesteric liquid crystals

Abstract

Prior examinations have reported that polymer stabilisation of azobenzene-based cholesteric liquid crystal (CLC) mixtures can reduce the time necessary for complete colour restoration in the dark from three days to as few as five minutes. This work extends upon these prior examinations by exploring and elucidating the role of crosslinker concentration and monomer polarity on the colour restoration of a representative CLC mixture composed of a high HTP bis(azo) binapthanyl chiral dopant (QL76) mixed into the cyanobiphenyl nematic liquid crystal host MDA-00-1444. The impact of these variables was unexpectedly convoluted. In all the formulations examined here, polymer stabilisation dramatically reduces the time for complete colour restoration of the starting reflection notch. In mixtures based on nonpolar liquid crystal monomers, increasing the crosslinker concentration reduces the time necessary for complete colour restoration. However, the dependence on crosslinker concentration reverses in mixtures composed from polar liquid crystal monomers in which increasing the crosslinker concentration serves to increase the time necessary for complete colour restoration.

Keywords:

• cholesteric liquid crystal
• chiral nematic
• azobenzene
• photochemistry

Acknowledgements

We gratefully acknowledge funding from the Air Force Office of Scientific Research and the Materials and Manufacturing Directorate of the Air Force Research Laboratory. We thank Quan Li for providing the QL76 material used in this examination.