Reverse-mode polymer dispersed liquid crystal films prepared by patterned polymer walls

Abstract

This article proposes a methodology to prepare polymer dispersed liquid crystal (PDLC) films working in the reverse-mode operation, where the ion-doped nematic liquid crystals (NLCs) with negative dielectric anisotropy (Δε) were locked by polymer walls. On-state and off-state of films were controlled by an electric field. In the absence of an electric field, it appears to be transparent. In the field, the homogeneous alignment NLCs form dynamic scattering, giving rise to opaque. The effect of the cylindrical holes with different diameters of photo masks and liquid crystal Δε on the electro-optical properties and transmittance wavelength range of 400-3000 nm light of samples were investigated. It was found that it exhibited very good electro-optical characteristics, high contrast ratio and excellent infrared energy-efficient of films used as switchable windows.Keywords: reverse-mode polymer dispersed liquid crystal; polymer walls; nematic liquid crystal; negative dielectric anisotropy; electro-optical properties IntroductionPolymer dispersed liquid crystal (PDLC) films are technologically important class of materials that find numerous applications as electrically switchable optical devices.[1-3] PDLC films are formed by liquid crystal (LC) microdroplets embedded in a polymer matrix. They can exhibit either a droplet morphology in which droplets of LC are embedded in a polymer matrix, or a polymer ball morphology in which the LC takes up the voids and the crevices of a network structure formed by small polymer balls. In the normal-mode operation, they are in an opaque state (offstate) and can be turned into a transparent state (onstate) by controlling the LC molecule orientation by means of a suitable voltage. The reverse-mode PDLC films are transparent in its off-state and can be turned into an opaque on-state. A greater interest has been aroused by reverse-mode PDLC films that are useful as switchable windows, automotive applications [4,5] and used in a wide range of applications that need a transparent state in the absence of any applied voltage.Several authors have reported examples of reverse-mode PDLC films obtained by modification of the polymer surface energy,[6] by functionalising the LC/polymer matrix interface,[7] by using dualfrequency addressable LC,[8] by means of rough surfaces [9,10] or by increasing the LC content. [11]

Reverse Mode Polymer-Stabilized Liquid Crystal Films via Thiol and Acrylic Azobenzene

“…On the other hand, the initial transparent state of RPSLC films offers several advantages, such as energy saving and privacy protection with no fields. So far, RPSLC films have been realized through homogeneous alignment with polymer-stabilized positive dielectric anisotropic (+Δε) nematic or cholesteric LCs and homeotropic alignment with polymer-stabilized negative dielectric anisotropic (−Δε) LCs using a variety of techniques including patterned polymer walls, photoalignment, application of a magnetic field or low-frequency electric field, and doping of surface-aligning polymers. − Furthermore, RPSLC films are mainly prepared via photo- or thermal polymerization methods. Nevertheless, the former method is technologically more important because it allows the freezing of accurate orientational order at the desired temperature within the nematic state.…”

Preparation of Highly Durable Reverse-Mode Polymer-Stabilized Liquid Crystal Films with Polymer Walls

“…With an applied electric field, the LC molecules prefer to rotate and the polymer networks will disturb and impede the rotation of LC molecules. Multi-domain structures will be formed and the incident light will be scattered, causing the device to become opaque. , The reverse-mode electrically switchable light-transmittance controllable films are prepared mainly by the PSLC systems based on nematic LCs, − cholesteric LCs − or dual frequency LCs . In PSLC, LC is the major component and is confined by networks of a small amount of polymer (ca.…”

Thermoresponsive Reflective Scattering of Meso-Scale Phase Separation Structures of Uniaxially Orientation-Ordered Liquid Crystals and Reactive Mesogens

“…PNLC nonuniform structures that control light scattering have often been fabricated via a self-organizing process called photopolymerization-induced phase separation (PPIPS). − Through PPIPS during light exposure, LCs locally segregate from monomers during polymerization, and consequently, an optically nonuniform distribution of LC and polymer domains is formed. Although many studies of light scattering from PNLCs have paid attention only to opaqueness, some research groups are investigating light scattering properties, that is, the dependence of light scattering on angles of incidence and scattering, on optical polarization, and on wavelength. ,,− Light diffusers for homogenizing, expanding, and guiding incoming light have been developed with PNLCs for broad applications such as backlit displays, wide-area printing, and smart windows.…”