Chemical-Physical Characterization of a Binary Mixture of a Twist Bend Nematic Liquid Crystal with a Smectogen

Abstract

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.

On the measurement of the bend elastic constant in nematic liquid crystals close to the nematic-to-SmA and the nematic-to-NTBphase transitions

“…More precisely κ 31 decreases till a minimum is reached before increasing again when the temperature decreases and tends to T N B . This behavior was already observed by other authors in pure CB7CB [5] and in mixtures of 8CB/CB7CB [6] and was attributed to the presence of cybotactic groups of lamellar-like N TB phase in the nematic phase [5]. The surprising point here is that our values of κ 31 are extremely small in the vicinity of the N TB phase, smaller than all the values reported before in similar mixtures.…”

“…[3]). These measurements are interesting in itself because K 3 diverges and becomes very large close to the SmA phase [2,4], whereas it is very small and has a non-monotone behavior close to the N TB phase [5,6]. In practice, the experiment consists of measuring the capacitance of a planar sample as a function of the applied voltage at different temperatures, and then to fit these curves with the adequate theoretical model.…”

Micro-structural investigations on oppositely charged mixed surfactant gels with potential dermal applications

“…S2 , Table S1 A) 44 – 47 . Nematic liquid textures originate from thread-like shapes, that correspond to surfactant gels aligning themselves in threadlike shapes as reported earlier 48 . The patterns become more complex with enhanced sizes due to the aggregation and associative interactions between AASs and HTAB.…”

Methylene- and thioether-linked cyanobiphenyl-based liquid crystal dimers CBnSCB exhibiting room temperature twist-bend nematic phases and glasses

“…87 For characterization and application purposes, it is necessary to develop materials that exhibit the N TB phase over a wide temperature range, the room-temperature N TB phase, and its glass phase or N TB glass (N TB G). 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.…”