Thermal phase transition behaviours of the blue phase of bent-core nematogen and chiral dopant mixtures under different boundary conditions

Abstract

We have investigated dramatic changes in the thermal phase transition of a liquid-crystalline (LC) blue phase (BP) consisting of bent-core nematogen and chiral dopants under various boundary conditions during cooling from the isotropic phase. Blue phase III, which has arbitrary morphological characteristics, between two glass plates goes to blue phase I, which has a body-centred cubic structure, when the sample is placed on the glass as a droplet form. These two distinctive phase transition behaviours were directly observed by polarized optical microscopy as well as selective reflection spectroscopy, in which the phase transition between BPs started from the air/LC interface. We determined that this transition resulted from the ordered double-twisted cylinders near the air-boundary by confocal laser-scanning microscopy.

Polymer Stabilization of Liquid-Crystal Blue Phase II toward Photonic Crystals

“…LC cubic BPs have attracted significant research interest because they have potential for application in advanced photonic devices as three-dimensional (3D) PCs . Cubic BPs have a double-twisted cylinder (DTC) structure, and the self-assembly of DTCs in 3D space determines their peculiar periodic lattice structures. , Cubic BPs can be categorized into two types, namely, a simple-cubic BP (BPII) and a body-centered-cubic BP (BPI), in the order of decreasing temperature. ,,, In general, each cubic BP makes a brief appearance, typically 0–2 °C, in the temperature range between the high-temperature isotropic (Iso) phase and the low-temperature N* phase. This narrow temperature range limits their utility in practical applications.…”

“…8,9 Cubic BPs can be categorized into two types, namely, a simple-cubic BP (BPII) and a bodycentered-cubic BP (BPI), in the order of decreasing temperature. 2,8,10,11 In general, each cubic BP makes a brief appearance, typically 0−2 °C, in the temperature range between the high-temperature isotropic (Iso) phase and the low-temperature N* phase. This narrow temperature range limits their utility in practical applications.…”

Clusters of B7 Fibers Reveal Origin of Blue Phase Stability in a Binary Mixture of Chiral Rod-like and Achiral Bent-Core Molecules

“…Several strategies are being employed in order to widen the temperature range of BPs and make them viable for device fabrication. , Apart from long-range BPs observed with compounds having dimeric molecular structures, stabilization of BPs has been obtained in composite systems consisting of polymers and LCs , or by incorporation of nanoparticles (NPs). , A hybrid system consisting of a polymer-stabilized BP into which NPs have been doped has been found to further enhance the temperature stability of the BPs . A special feature associated with LCs made of bent-core (BC) molecules is the generation of chirality in spite of the molecules being achiral. , Another approach that has been adopted is to induce BPs by mixing an LC made of achiral BC molecules exhibiting a nematic (N) phase with a N* LC or a nonmesomorphic chiral dopant. − BCLCs have been found not only to enhance the temperature range of the BPs but also to contribute to an enhanced Kerr constant. − LC dimers formed by linking an achiral BC unit with a chiral rod-like (R) unit via a flexible spacer have been found to possess high molecular chirality, resulting in the formation of a long-range BPIII phase . Stabilization of BPs has been obtained by hydrogen-bonded bent-shaped and T-shaped molecules, featuring a branched terminal group .…”

“…The B 7 phase is also one in which macroscopic chirality is manifested in the form of helical filaments. Free standing fibers, which can be obtained in the B 7 phase by mechanical pulling of bulk material using needles, also have a helical nature. , It can therefore be expected that using a BCLC exhibiting the lamellar B 7 phase could lead to stronger chiral effects which may aid in stabilizing BPs rather than SmCP phases or BC nematics (BCN), which have been used earlier. − …”