On the effect of alignment layers on blue phase liquid crystals

Abstract

In the present work, the effect of alignment layers on blue phase liquid crystals was investigated. It was found that homogeneous alignment layers have profound selective influence on blue phase II (BPII). In the absence of alignment layers, BPII domains were randomly oriented and showed weak Bragg reflection in the UV, whereas with assistance of anchoring uniform domains with sharp Bragg reflection in the visible range appeared. On the other hand, the magnitude of Bragg shift in response to alignment layers in BPI is negligible. Domains of BP with alignment layers exhibit sharp Bragg reflection peaks (with FWHM < 15 nm), with very vivid colors and possessing fast switching speeds (<5 ×10−4 s). This simple method of selectively assisting one of the cubic phases is expected to be advantageous in the comparative studies of the two phases.

Monodomain Blue Phase Liquid Crystal Layers for Phase Modulation

“…By performing the polymerization process at an extremely slow rate, we were able to maintain the alignment and orientation of the BP layers undisturbed after finishing the process. The UV irradiance is at least one order of magnitude lower than previously described polymerization methods11718.…”

Effect of Sectional Polymerization Process on Tunable Twist Structure Liquid Crystal Filters

“…The precursor mixtures were filled into empty cells with a thickness of 10 µm comprised of two ITO glass substrates with antiparallel polyimide alignment layers at 368 K. The polyimide alignment layers had the effect of enhancing the intensity of reflection because of its surface pinning effect [33][34][35]. The mixtures were cooled from isotropic phase to chiral nematic phase using a temperature controller (HCS302, Instec Co., Boulder, Colorado, USA).…”

“…For example, the black curve in Figure 2a represents the polymerization process during which the cell was cooled from 345 K to 338 K at a rate of 7 K/min, placed at 338 K for 15 minutes, cooled to 323 K at a rate of 7 K/min, and finally polymerized at 323 K. The bandwidth referred to the full width at half maximum (FWHM) as well as the 3 dB bandwidth [36]. Among the curves with the polymerization process at different holding time, the curves with the holding time of 45 minutes had the widest bandwidth due to the stabilization effect of the longtime holding treatment [32][33][34]. The curves with a holding treatment at 338 K showed wider bandwidth than those at other temperatures because of the larger temperature difference between the holding temperature and the cured temperature.…”

“…Compared with the conventional polymerization process [23,31], the process of holding at a fixed temperature for a fixed time is added in the sectional polymerization process. Prolonging the holding time is effective at improving the homogeneous alignment of the LC material, which can improve the Bragg reflection of the filter [32][33][34]. Considering this effect, the sectional polymerization process with a holding treatment is used to increase the bandwidth of filter without distortion.…”

The influence of orienting layers on blue phase liquid crystals in rectangular geometries

“…The obtained results show that the orientation layers have a significant effect on the optical properties of the blue phase. Usually, in BPII, a light reflection appears for lower wavelengths than in BPI [12][13][14]. In such a case, a green or blue light reflection is observed.…”