Electrically Switchable, Hyper‐Reflective Blue Phase Liquid Crystals Films

Abstract

amorphous phase, whereas BPII and BPI possess double-twisted cylinders arranged in a cubic crystalline structure with simple cubic and body-centered cubic symmetry, respectively. [3,4] BPLCs have attracted people's interest for many potential applications, such as field-sequential displays, [5,6] full-color reflective displays, [7,8] electrically switching devices, [9][10][11][12] tunable photonic crystals, [13,14] phase modulator optical devices, [15][16][17] as well as soft templates for 3D colloidal crystals. [18] The intrinsic features of blue phases include a submillisecond response time, optically isotropic dark state, and periodic helical structure on the order of the visible wavelength.Because only circularly polarized incident light with the same handedness as that of the BPLC will be reflected, the reflectance of a single BPLC film for unpolarized or linearly polarized incident light is limited to 50%. Recent reports have shown that it is possible to increase the reflectance by assembling one BPLC template with another reflective layer, such as a BPLC or cholesteric liquid crystal (CLC), with opposite handedness. The increased reflectance of BPLCs is critical to applications such as reflective displays, color filters, lasers, and mirrors. The BPLC template, which was firstly proposed by Castles et al., [19,20] was a free-standing porous material fabricated by reactive mesogens and liquid crystals in BP. It was used to form a stretchable and flexible BPLC film by refilling liquid crystal. [19,20] H. C. Jau et al. studied the electrooptical properties of templated blue phase liquid crystals as well as the effects of the helical twisting power of the filling mesogen on electro-optical properties. [21] The transfer of the orientational order of the blue phase to the surface of the polymer matrix and the resulting surface anchoring were numerically modeled. [22] Based on the BPLC template, Guo et al. reported a double-layer BPLC film with a segregation of the left-handed (LH) and right-handed (RH) domains across the LC film to reflect both left-and right-circularly polarized light. [23,24] In Guo's paper, two kinds of double-layer structures were demonstrated: one was fabricated using a R-BPLC template and a L-BPLC template, with a reflectance of 25%; another was fabricated using a R-BPLC template and a pure L-CLC, with a reflectance of 36%. The low reflectances are partially due to the low reflectance of the single BPLC film formed in BPI and partially Blue phase liquid crystals (BPLCs) with three-dimensional periodicity have attracted significant attention due to their fast response time in the submillisecond region, which is critical in sequential liquid crystal displays and fast switchable photonic devices. However, the reflectivity of single-layer BPLC films in the visible range, which is generally used for reflective display, is still low and limited to 50%, which hinders its use in a wide range of applications. Herein, hyper-reflective, electrically switchable, fast responsive, and colorful reflective...

Retention and deformation of the blue phases in liquid crystalline elastomers

“…The cubic blue phases have been extensively studied in noncross-linked low molar mass systems [20][21][22][23][24][25][26][27] . The primary motivation for these studies is the potential for fast electro-optical switching properties in devices that do not need alignment layers or precise thickness control 28 .…”

3D Chiral Photonic Nanostructures Based on Blue‐Phase Liquid Crystals

“…Xu et al reported electrically switchable, hyper‐reflective, and fast‐responsive displays based on multilayer BP films containing two single‐layer BP templates with opposite handedness and an interlayer between them ( Figure a,b). [ 156 ] Red, green, and blue films with hyper‐reflectivities of 89, 82, and 68% were obtained by refilling achiral nematic liquid crystals into the multilayer BP templates (Figure 12c). In addition, reflectance switching of the film was realized by the local director reorientation of the liquid‐crystal molecules in a 1 V μm −1 electric field.…”

High-Reflective Templated Cholesteric Liquid Crystal Filters

“…Because the reflection by the CLCs with a helical structure is selective, only circularly polarized incident light with the same handedness as that of CLC is reflected, while light with the opposite handedness is transmitted. Accordingly, for the unpolarized or linearly polarized incident light, the reflectance of a single CLC film is equal to, at most, 50% [11,18]. However, a higher reflectivity of a CLC device is desired to apply in many fields, including reflective display, lasing and mirrors, especially in optical filters.…”