“…In sealed cells, however, 8CB/CB7CB mixtures in the range 40 wt % < φ < 55 wt % exhibited room temperature N TB phases that were observed to be metastable for at least 6 months in XRD capillaries and optical cells. It should be noted that, if other studies have already reported low temperature N TB phases in mixtures [16][17][18]47], many of them tend to rapidly crystallize at room temperature [20]. This feature allowed us to characterize the 8CB/CB7CB system in detail.…”
Nematic twist-bend phases (NTB) are new types of nematic liquid crystalline phases with attractive properties for future electro-optic applications. However, most of these states are monotropic or are stable only in a narrow high temperature range. They are often destabilized under moderate cooling, and only a few single compounds have shown to give room temperature NTB phases. Mixtures of twist-bend nematic liquid crystals with simple nematogens have shown to strongly lower the nematic to NTB phase transition temperature. Here, we examined the behaviour of new types of mixtures with the dimeric liquid crystal [4′,4′-(heptane-1,7-diyl)bis(([1′,1″-biphenyl]4″-carbo-nitrile))] (CB7CB). This now well-known twist-bend nematic liquid crystal presents a nematic twist-bend phase below T ≈ 104 °C. Mixtures with other monomeric alkyl or alkoxy -biphenylcarbonitriles liquid crystals that display a smectic A (SmA) phase also strongly reduce this temperature. The most interesting smectogen is 4′-Octyl-4-biphenylcarbonitrile (8CB), for which a long-term metastable NTB phase is found at room and lower temperatures. This paper presents the complete phase diagram of the corresponding binary system and a detailed investigation of its thermal, optical, dielectric, and elastic properties.
“…In sealed cells, however, 8CB/CB7CB mixtures in the range 40 wt % < φ < 55 wt % exhibited room temperature N TB phases that were observed to be metastable for at least 6 months in XRD capillaries and optical cells. It should be noted that, if other studies have already reported low temperature N TB phases in mixtures [16][17][18]47], many of them tend to rapidly crystallize at room temperature [20]. This feature allowed us to characterize the 8CB/CB7CB system in detail.…”
Nematic twist-bend phases (NTB) are new types of nematic liquid crystalline phases with attractive properties for future electro-optic applications. However, most of these states are monotropic or are stable only in a narrow high temperature range. They are often destabilized under moderate cooling, and only a few single compounds have shown to give room temperature NTB phases. Mixtures of twist-bend nematic liquid crystals with simple nematogens have shown to strongly lower the nematic to NTB phase transition temperature. Here, we examined the behaviour of new types of mixtures with the dimeric liquid crystal [4′,4′-(heptane-1,7-diyl)bis(([1′,1″-biphenyl]4″-carbo-nitrile))] (CB7CB). This now well-known twist-bend nematic liquid crystal presents a nematic twist-bend phase below T ≈ 104 °C. Mixtures with other monomeric alkyl or alkoxy -biphenylcarbonitriles liquid crystals that display a smectic A (SmA) phase also strongly reduce this temperature. The most interesting smectogen is 4′-Octyl-4-biphenylcarbonitrile (8CB), for which a long-term metastable NTB phase is found at room and lower temperatures. This paper presents the complete phase diagram of the corresponding binary system and a detailed investigation of its thermal, optical, dielectric, and elastic properties.
“…33 Scanning electron microscopy observations of the photo-crosslinked samples of the N TB phase revealed a helical organization of the nanostructures. [34][35][36] In addition to the N TB phase, other structurally associated mesophases, such as heliconical smectic (Sm) phases based on bent-core molecules 37,38 and bent LC dimers, 39,40 the twist grain-boundary-twistbend nematic phase, 41 and the splay-bend N (N SB ) phase electrically induced from the N TB phase [42][43][44] have been experimentally verified. Furthermore, the splay N (N S ) phase with the modulation rotated 90° with respect to the N SB phase was discovered in some rod-like mesogens.…”
Section: Introductionmentioning
confidence: 99%
“…Using mixtures with other mesogens is a useful method to lower the N-N TB phase-transition temperature, 18 ultimately achieving a metastable room temperature N TB phase 88 and its photocrosslinked state. 35 However, the formation of room-temperature N TB materials from their single-component systems indeed remains a rarity. 50,61,64,67,68,70,72 This has restricted deep structural analyses and examination of the physical properties of the N TB phases, in addition to the development of new applications.…”
The twist-bend nematic (NTB) phase is a new heliconical liquid crystal (LC) phase that is associated with spontaneous symmetry breaking for achiral bent LC molecules. Herein, we demonstrate a homologous...
“…The latter observation was made with toroidal FCDs as well (Figure S2f, Supporting Information). To circumvent the longstanding issue of electric irreversibility of SmA FCDs, we build from prior studies of polymerization of LCs [ 8,22–24 ] and evaluate the ability of a new approach based on polymerization of SmA FCDs and electric reversibility of NLCs. To illustrate the potential of such an approach to increment new properties arising from the structure and organization of SmA FCDs with electric reversibility and dynamic adjustability, we use linear arrays of EHFCDs.…”
Section: Resultsmentioning
confidence: 99%
“…[ 13 ] Another way to reversibly switch or reconfigure SmA defect patterns consists in combining electric fields and thermal annealing from the N or isotropic (I) phases, [ 20,21 ] yet this again prevents from dynamic adjustability. Moreover, strategies like in situ polymerization of LCs, successfully applied to improve the physical properties of blue phase, [ 22 ] cholesteric, [ 23 ] and nematic structures, [ 8,24 ] have not been used to this end for SmA defect patterns so far.…”
Shaping liquid crystals (LCs) into arrays of defect patterns enables the design of composite materials with new stimuli‐responsive properties. Self‐assembled defect assemblies that may arise in layered smectic A (SmA) LCs such as focal conic domains (FCDs), exhibit remarkable optical features and abilities for ordering nanoparticles. However, such SmA defect patterns are essentially electrically irreversible, which currently limits their adjustability in a dynamic way. Here, in situ polymerization of the texture of SmA FCDs allows transferring them into more electrically responsive LC phases, such as nematic, making possible a dynamic switch between different textural and optical states of FCDs in a reversible manner with voltage. Moreover, the method readily enables to program the operating temperature range of the polymer/LC composite from its chemical composition, adapting the system to various potential uses. This approach may increment new applications of SmA defect patterns such as voltage‐tunable privacy layers and may further inspire the design of LC‐based nanostructured composite and hybrid materials with new functions that can be dynamically tuned with voltage.
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