Blue Phase Liquid Crystal Device Research Articles

Polymer-stabilized blue phase liquid crystal devices with ultra-low hysteresis and driving stability

Hysteresis is a critical factor that plays a significant role in determining the electro-optical performance of display devices, especially in polymer-stabilized blue phase liquid crystal devices (PSBPLCDs). The presence of hysteresis limits the accuracy of device operation and affects its long-term stability. To address this challenge, we have employed a few short-chain monofunctional methacrylate monomers at an appropriate concentration to form microscale network holes in PSBPLCDs. These PSBPLCDs with microscale network holes show low hysteresis (<0.5 %) for networks with non-smooth surfaces and even ultra-low hysteresis (∼0.02 %) for networks with smooth surfaces. The PSBPLCDs exhibit a wide temperature range exceeding 85 °C and have similar response times to that of conventional PSBPLCDs. Moreover, these PSBPLCDs have a low hysteresis and small residual birefringence even after undergoing 2,000,000 driving cycles. These research results are significant in determining the appropriate selection of monofunctional monomers for the design and development of PSBPLCDs.

Paper No S5.3: Importance of Alignment Layers in Blue Phase Liquid Crystal Devices

AbstractIn this article, we present how alignment layers affect blue phase liquid crystals and how we can use this effect to our advantage.

10.1: A Microsecond‐Response Blue Phase Liquid Crystal Device

AbstractA polymer‐stabilized blue‐phase liquid crystal (BPLC) with microsecond response time is demonstrated using a vertical field switching cell. The measured decay time is 39.4 μs at room temperature (21°C) and then decreases to 9.6μs at 44.3°C. Such a response time is 1–2 orders of magnitude faster than that of a typical BPLC device. The responsible physical mechanisms are the collective effects of short pitch length, strong polymer network, and low viscosity through elevated temperature effect. The on‐state voltage of our BPLC device is 44.2 V, hysteresis is below 0.7%, and contrast ratio is over 1300:1.

Critical Field for a Hysteresis-Free BPLC Device

A correlation between the peak electric field and hysteresis of a polymer-stabilized blue-phase liquid crystal (BPLC) is found experimentally. If the peak electric field is below ~ 5 V/μm, hysteresis is negligible. Based on this guideline, we propose elliptical protrusion electrodes to reduce peak electric field which in turn eliminates hysteresis while keeping a high transmittance. Such a hysteresis-free BPLC device is highly desirable for display and photonic applications.

A microsecond-response polymer-stabilized blue phase liquid crystal

A polymer-stabilized blue-phase liquid crystal (BPLC) with microsecond response time is demonstrated using a vertical field switching cell. The measured decay time is 39 μs at room temperature (21 °C) and then decreases to 9.6 μs at 44.3 °C. Such a response time is 1-2 orders of magnitude faster than that of a typical BPLC device. The responsible physical mechanisms are the collective effects of short pitch length, strong polymer network, and low viscosity through temperature effect. The on-state voltage of our BPLC device is 44.2 V, hysteresis is below 0.7%, and contrast ratio is over 1300:1.

Determination of Polar Anchoring Strength for Polymer-Stabilized Blue Phase Liquid Crystal Device

Quantitative evaluation of a coupling coefficient between the blue phase (BP) liquid crystal (LC) and the diacrylate-type polymer, which is to be either the framework or the defect line of the polymer-stabilized (PS) BPLC, is an important subject. As a coupling coefficient, the polar anchoring strength Wd between the BPLC and the diacrylate-type polymer prepared inside a thin hybrid alignment nematic (HAN) cell was evaluated by means of oblique incidence transmission spectroscopic ellipsometry. As an example, the polar anchoring strength Wd = 1.87 ×10-4 J/m2 is measured at the interface between host BPLC material with the diacrylate-type polymer performing vertical alignment (VA).

Determination of Polar Anchoring Strength for Polymer-Stabilized Blue Phase Liquid Crystal Device

Quantitative evaluation of a coupling coefficient between the blue phase (BP) liquid crystal (LC) and the diacrylate-type polymer, which is to be either the framework or the defect line of the polymer-stabilized (PS) BPLC, is an important subject. As a coupling coefficient, the polar anchoring strength Wd between the BPLC and the diacrylate-type polymer prepared inside a thin hybrid alignment nematic (HAN) cell was evaluated by means of oblique incidence transmission spectroscopic ellipsometry. As an example, the polar anchoring strength Wd = 1.87 ×10-4 J/m2 is measured at the interface between host BPLC material with the diacrylate-type polymer performing vertical alignment (VA).

Domain growth in cholesteric blue phases: Hybrid lattice Boltzmann simulations

Here we review a hybrid lattice Boltzmann algorithm to solve the equations of motion of cholesteric liquid crystals. The method consists in coupling a lattice Boltzmann solver for the Navier-Stokes equation to a finite difference method to solve the dynamical equations governing the evolution of the liquid crystalline order parameter. We apply this method to study the growth of cholesteric blue phase domains, within a cholesteric phase. We focus on the growth of blue phase II and on a thin slab geometry in which the domain wall is flat. Our results show that, depending on the chirality, the growing blue phase is either BPII with no or few defects, or another structure with hexagonal ordering. We hope that our simulations will spur further experimental investigations on quenches in micron-size blue phase samples. The computational size that our hybrid lattice Boltzmann scheme can handle suggest that large scale simulations of new generation of blue phase liquid crystal device are within reach.