Modification of the Electro-Optical Properties of Liquid Crystal Devices in the Inverse Mode

An optical device operating in the inverse mode for the transmission of light radiation has been developed, fabricated using a liquid crystal with positive dielectric anisotropy and characterized by a high transmittance. It has been established that improvement of the electro-optical properties, achieved by modifying the polymer–liquid crystal interface, leads to an increase in the optical transmittance of the films up to 80%. This effect is interpreted as a memory effect arising both from the mechanical influence of aligned polymer chains and from the reorientation of the liquid crystal director under the action of an internal built-in electric field. A new approach to the fabrication of polymer-dispersed liquid crystal (PDLC) systems operating in the inverse mode has been proposed. This approach is realized through the formation of a long-term, stable internal DC electric field in a PDLC initially operating in the normal mode and doped with metallic nanoparticles. The incorporation of nanoparticles enables the generation of strong internal DC electric fields within the PDLC and facilitates the formation of a uniformly aligned director configuration of the nematic liquid crystal 5CB, with an OFF-state transmittance of up to 75%. The combination of the internal DC electric field with an external electric field (E_ext = 1 V/µm) results in a randomization of the liquid crystal director, thereby switching the device into an opaque ON state. The proposed device overcomes several limitations inherent to inverse-mode PDLC systems based on liquid crystals with negative dielectric anisotropy (Δε < 0), such as the lack of commercially available materials with the required physicochemical properties. The excellent electro-optical performance demonstrated by this device may be advantageous for the development of electrically switchable chromogenic materials and the fabrication of smart windows.