Colorable Light-Scattering Device Based on Polymer-Stabilized Ion-Doped Cholesteric Liquid Crystal and an Electrochromatic Layer

Abstract

Bistable polymer-stabilized cholesteric liquid crystal (LC) devices have been extensively researched due to their energysaving benefits. Compared to devices with merely transparent and light-scattering states, LC devices with controlled light absorption or changeable color functions are unquestionably more intriguing. In this paper, a polymer-stabilized ion-doped cholesteric LC and an electrochromic layer are used to fabricate a colorable device which can show four operating states: transparent, light-scattering, colored transparent, and colored light-scattering. The working principle and fabrication strategy are explained in detail. Based on the dielectric response of LC, the electrohydrodynamic effect of ion-doped LC, and the redox reaction of electrochromic materials, the transparent or light-scattering state and the colored or colorless state of the device can be regulated by controlling the alternating frequency and the direction of the electric field. The display performance related to the monomer, chiral dopant, and electrochromic layer is investigated. The content of monomer and chiral dopant affects the polymer network and pitch of cholesteric LC, which then affects the driving voltages and contrast ratio. The thickness of the electrochromic layer has a significant impact on the transmittance of the device's coloring and fading states. The sample with excellent operating states is obtained by optimizing the material and the construction, which can be widely applied in smart windows and energy-saving display devices.

Recent Advances in Electro-Optic Response of Polymer-Stabilized Cholesteric Liquid Crystals

“…In the case of PSCLCs, a bistable switching effect can be attained by using either positive Δε or negative Δε LC hosts, depending on the processing conditions. Bistable switching PSCLCs have two modes: normal mode [ 5 , 18 , 19 , 36 , 37 ] and reverse mode [ 5 , 20 , 21 , 36 , 37 , 38 ]. In normal mode, the PSCLC switches from a scattering state to a clear state.…”

“…The polymer network of PSCLCs can also lock the pitch of a CLC, and it affects various optical responses. Stabilizing low molar mass CLCs with positive Δε using polymer networks allows for fast and bistable switching between reflective and scattering textures [ 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 36 , 37 , 38 ]. These composite systems are described as PSCLCs, but, in the past, these systems were also known as polymer-stabilized cholesteric textures (PSCTs).…”

Structural coloured epoxy resin patterns prepared using thermochromic epoxy liquid crystal mixtures

“…[1][2][3][4] Since the wavelength of the selective Bragg reflection band of the CLCs is sensitive to various external stimuli, CLCs have been widely used in sensors, filters and reflective devices. [5][6][7][8][9][10][11][12][13] Liquid crystal polymer network (LCN) is a polymer network formed by the in situ polymerization of the reactive liquid crystal monomers. 14,15 If this polymerization is carried out at the cholesteric phase, a cholesteric LCN (CLCN) is obtained.…”

Hybrid Active–Passive Control of an Unconventional Smart Window Based on Dye‐Doped Dual‐Frequency Liquid Crystal

“…However, most of the LC‐based smart windows developed so far exhibit only one single operational function, typically possessing an electric control approach for users. [ 39–41 ] Nevertheless, some recent studies have reported the feasible evolution of LC‐based smart windows with passive control, which can achieve truly “smart” functionality by responding to changes in temperature T (thermoresponsive) [ 42,43 ] or light (photoresponsive). [ 44–46 ] It is an effective means to devise a passive‐control LC smart window by incorporating photoisomerizable (e.g., azobenzene), [ 36,47 ] photothermal (e.g., isobutyl‐substituted diimmonium borate), [ 43 ] or photoconductive substances (e.g., zinc phthalocyanine) [ 48 ] that can respond to environmental stimuli.…”

“…However, most of the LC-based smart windows developed so far exhibit only one single operational function, typically possessing an electric control approach for users. [39][40][41] Nevertheless, some recent studies have reported the feasible evolution of LC-based smart windows with passive control, which can achieve truly "smart" functionality by responding to changes in temperature T (thermoresponsive) [42,43] or light (photoresponsive). [44][45][46] It is an effective means to devise a passive-control LC smart…”