The Shape of Things To Come: The Formation of Modulated Nematic Mesophases at Various Length Scales

Abstract

The twist–bend nematic (NTB) phase is a recently discovered liquid‐crystalline phase that exhibits macroscopic chirality even when formed from achiral materials, and as such presents a unique testbed for studies concerning the spontaneous breaking of mirror symmetry in soft matter. It is primarily exhibited by materials for which the molecular structure is composed of two rigid aromatic units (such as biphenyl connected by a flexible spacer). The local structure of the NTB phase is nematic‐like—with molecules having an average orientational order but no positional order—with a nanoscale helix in which the pitch (i.e., the repeat distance of the helix) is of the order of several nanometres. A helix is chiral, and so the bulk NTB phase—in the absence of a biasing chiral environment—spontaneously separates into macroscopic domains of opposite handedness. After discussing the structure of this mesophase and its elucidation, this concept article presents the molecular factors that determine its incidence. The apparent dependency primarily on molecular shape and bend angle rather than particular functional group combinations manifests in this mesophase being exhibited on length scales far beyond those of simple liquid‐crystalline dimers, not only in oligomers and polymers, but also in aqueous suspensions of micron sized helical particles.

Seeing the Unseen: The Role of Liquid Crystals in Gas‐Sensing Technologies

“…[ 60 ] Currently, they have been attracting an increasing interest from researchers because they exhibit alternate novel mesophases. [ 61–63 ]…”

Rational Design of Rod‐Like Liquid Crystals Exhibiting Two Nematic Phases

“…The nematic liquid‐crystalline state—as was exhibited by low‐molar‐mass liquid crystals—is characterised by relatively high fluidity, a lack of positional ordering of molecules, but with short‐range orientational order. Transitions from one nematic phase into another are rare, but also highly topical due, in part, to the recent discovery of the twist‐bend nematic phase . Several other nematic or nematic‐like mesophases are known to exist (chiral nematic (N*), discotic nematic (N D ), re‐entrant nematic (N RE ), biaxial nematic (N B ), blue phases (BPI, BPII, BPIII)) or are either predicted to exist or have possibly been discovered (cubatic nematic (N cub ), splay‐bend nematic (N SB )).…”

Conformational landscapes of bimesogenic compounds and their implications for the formation of modulated nematic phases

“…A number of reviews concerning the twist-bend phase have been published recently [18][19][20]. A relatively large number of dimeric liquid crystals are known to exhibit this state of matter [1,3,8,9,11,12,[21][22][23][24][25][26][27][28][29][30], and there is a growing number of liquid-crystalline oligomers known to exhibit the twist-bend phase [18,[31][32][33][34]. Additionally, this phase has been observed in a phenylpiperazine derived bent-core liquid crystal [4].…”