Abstract
Blue phase liquid crystals (BPLCs) composed of double-twisted cholesteric helices are promising materials for use in next-generation displays, optical components, and photonics applications. However, BPLCs are only observed in a narrow temperature range of 0.5–3 °C and must be stabilized with a polymer network. Here, we report on controlling the phase behavior of BPLCs by varying the concentration of an amorphous crosslinker (pentaerythritol triacrylate (PETA)). LC mixtures without amorphous crosslinker display narrow phase transition temperatures from isotropic to the blue phase-II (BP-II), blue phase-I (BP-I), and cholesteric phases, but the addition of PETA stabilizes the BP-I phase. A PETA content above 3 wt% prevents the formation of the simple cubic BP-II phase and induces a direct transition from the isotropic to the BP-I phase. PETA widens the temperature window of BP-I from ~6.8 °C for BPLC without PETA to ~15 °C for BPLC with 4 wt% PETA. The BPLCs with 3 and 4 wt% PETA are stabilized using polymer networks via in situ photopolymerization. Polymer-stabilized BPLC with 3 wt% PETA showed switching between reflective to transparent states with response times of 400–500 μs when an AC field was applied, whereas the application of a DC field induced a large color change from green to red.
Highlights
Blue phase liquid crystals (BPLCs), a three-dimensional photonic crystal structure, are highly twisted chiral nematic liquid crystals
We report the phase behavior of BPLCs and electro-optic response of polymer-stabilized BPLCs (PSBPLC) depending on the concentration of the amorphous crosslinking agent PETA
PETA in BPLC mixtures is mainly concentrated in the disclination lines, which inhibits the formation of the simple cubic blue phase-II (BP-II) structure and enhances the formation of the bodycentered cubic blue phase-I (BP-I) structure
Summary
Blue phase liquid crystals (BPLCs), a three-dimensional photonic crystal structure, are highly twisted chiral nematic (or cholesteric) liquid crystals. The director axes self-assemble into double-twisted cylinders (DTCs) with a diameter of several 100 nm [1–16]. The disclination defect is a discontinuous point where the cylinders are in contact [17]. During cooling from the isotropic phase, three blue phases can be observed as a function of the chirality of LC. Blue phase III (BP-III) is an amorphous DTC, whereas BP-II and BP-I phases are three-dimensional simple cubic (SC) and body-centered cubic (BCC) phases, respectively
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