Tunable reflective colors in holographically patterned liquid crystal gels

Abstract

Thin film holographic liquid crystal gratings are of great interest due to their controllable photonic properties. Holographic polymer dispersed liquid crystal (H-PDLC) with a polymer concentration of 40-90% is an example of a system where nonuniform irradiation is used to template alternating polymer-rich and polymer-poor regions with a periodicity related to the illumination wavelength. Here, we present a tunable holographic polymer stabilized liquid crystal (H-PSLC) reflection grating using a relatively small amount of polymer (6-20 wt%). Switching behavior from transparent to reflective state will be discussed by heating or applying an AC field. Heating above the isotropic temperature of the polymer-poor regions leads to the refractive index mismatch between the ordered LC polymer-rich regions and the disordered isotropic polymer-poor. Alternatively, the application of an AC field can be used as an Ohmic heat source to induce the thermal color change.