Two‐Step Photoalignment with High Resolution for the Alignment of Blue Phase Liquid Crystal

Abstract

The self‐assembling properties of liquid crystal (LC) are ideal for realizing switchable optical components. The director organization is strongly determined by the alignment at the substrate interfaces and photoalignment is a versatile method based on linearly polarized UV light. In this work, a two‐step photoalignment procedure is proposed to pattern the alignment at the surface. Illumination with uniform polarization or with an interference pattern is combined to obtain stripe patterns or square patterns of photoalignment. It can indeed be confirmed that the nematic director follows the varying azimuthal orientation. By increasing the angle between the two interfering beams, photoalignment with sub‐micrometer resolution is obtained, compatible with the dimensions of blue phase (BP) LC unit cell. Homogeneous domains of BP II with (100) or (110) crystal orientation are obtained and their Kossel patterns are recorded. The two‐step photoalignment technique allows to create patterns with high resolution and to control the orientation of BP LC, which is promising for photonic applications that require single domains.

Over 200 °C Broad‐Temperature Lasers Reconstructed from a Blue‐Phase Polymer Scaffold

“…Figure 1B-D presents the structure characterization of the as-prepared single-domain DD-PSBPLCs from BPI (110) crystal plane by transmission electron microscopy (TEM), Kossel diffraction, and synchrotron small-angle X-ray scattering (Syn-SAXS), respectively. There was a well-ordered periodic structure with a lattice constant of 249.02 nm (labeled a) from the TEM image, and a clear diffraction pattern with four arcs of ellipses (a typical pattern of BPI (110) crystal plane [66,67] ) in Figure 1C. Similarly, six diffraction spots derived from the Syn-SAXS pattern (Figure 1D 1 ) also proved the well-ordered structure of the as-prepared samples, with a lattice constant of 248.09 nm, as calculated from Figure 1D 2 [68] (Figure S2, Supporting Information), which agreed well with that from the TEM image (249.02 nm).…”

“…Kossel diffraction is known as a simple approach to characterize the crystal structures of BPLCs and the typical Kossel diffraction of BPI (110) plane features as one central circle and four ellipses [66,67,72,73] (Figure 6B The above phenomenon indicated that the BPI lattice parameters decreased, [74,75] as the phase transition occurred during the heating process from 70 to 230 °C (Figure 6A; Figure S28, Supporting Information). Figure 6B schemes the change trend of the BPI lattice size/Kossel diagrams with temperature, which could illustrate the blueshift of the stopband (excitation peak) of DD-PSBPLCs during the heating process.…”

Slanted Structure of Blue Phase II Self-Aligned on One-Dimensional Patterned Surfaces

“…Here, we discuss the three-dimensional periodicity of BPII and its slanted structure. Several studies have reported the control of BP lattice plane orientation by matching the periodicity of the BP structure with the periodicity of surface patterning. − In the model of the slanted structure assumed and demonstrated in this experiment, the BPII lattice shifted by one for each grating period. This model only considers the periodicity of BPII along the [001] crystal axis, i.e., the out-of-plane direction of the substrate, and does not consider the periodicity along the [100] crystal axis, i.e., the direction perpendicular to the grating, as shown in Figure c.…”

Large-scale single-crystal blue phase through holography lithography

“…The mismatches in polydomain BPs increase the scattering in the volume and affect the reflectivity of the Bragg reflection and the optical-electrical properties of BPs 25 – 29 Recent studies indicate that several methods, such as electric fields, 30 – 32 thermal control, 33 and surface treatments 34 – 36 can be applied to form monodomain BPs, which consist of many single-crystal platelets with one lattice plane orientated in the same direction. The structures of monodomain BPs significantly increase the reflectivity of the Bragg reflection.…”