Fast photo- and electro-optical switching of the polymer- stabilised cholesteric liquid crystal composite prepared by the template method

Multifunctional cholesteric liquid crystalline (LC) polymer-stabilised composite with photo- and electro-controllable photonic band gap was prepared and its fast photo- and electro-optical switching was demonstrated. The composite was prepared by a template method implying the polymerisation of cholesteric mixture consisting of several components, such as nematic liquid crystal compounds, chiral dopant, polymerisable mono- and diacrylates as well as photoinitiator. UV-induced polymerisation and subsequent removing of the low-molar-mass components enables to obtain porous cholesteric polymer matrix, which was used for filling with photochromic nematic mixture. Application of electric field or UV-irradiation shifts the photonic band gap to the short-wavelength spectral range. In the case of an electric field, this shift is associated with alignment of LC molecules along the electric field and deformation of the cholesteric helical structure. UV light action induces E-Z isomerisation of the azobenzene-containing molecules of photochromic mixture and decrease in their molecular anisometry leading to decrease in birefringence. Both electro- and photo-induced changes are completely reversible and switching the electric field off and/or irradiation with visible light completely recovers initial shape of selective reflection band. The switching is very fast and takes several seconds for the light action and less than one second for the electric field.