Liquid Crystal Dimers and Smectic Phases from the Intercalated to the Twist-Bend
In this review we consider the relationships between molecular structure and the tendency of liquid crystal dimers to exhibit smectic phases, and show how our application of these led to the recent discovery of the twist-bend, heliconical smectic phases. Liquid crystal dimers consist of molecules co...
| Main Authors: | , , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
MDPI AG
2022-09-01
|
| Series: | Crystals |
| Subjects: | |
| Online Access: | https://www.mdpi.com/2073-4352/12/9/1245 |
| _version_ | 1797489657733185536 |
|---|---|
| author | Corrie T. Imrie Rebecca Walker John M. D. Storey Ewa Gorecka Damian Pociecha |
| author_facet | Corrie T. Imrie Rebecca Walker John M. D. Storey Ewa Gorecka Damian Pociecha |
| author_sort | Corrie T. Imrie |
| collection | DOAJ |
| description | In this review we consider the relationships between molecular structure and the tendency of liquid crystal dimers to exhibit smectic phases, and show how our application of these led to the recent discovery of the twist-bend, heliconical smectic phases. Liquid crystal dimers consist of molecules containing two mesogenic groups linked through a flexible spacer, and even- and odd-membered dimers differ in terms of their average molecular shapes. The former tend to be linear whereas the latter are bent, and this difference in shape drives very different smectic behaviour. For symmetric dimers, in which the two mesogenic groups are identical, smectic phase formation may be understood in terms of a microphase separation into distinct sublayers consisting of terminal chains, mesogenic units and spacers, and monolayer smectic phases are observed. By contrast, intercalated smectic phases were discovered for nonsymmetric dimers in which the two mesogenic units differ. In these phases, the ratio of the layer spacing to the molecular length is typically around 0.5 indicating that unlike segments of the molecules overlap. The formation of intercalated phases is driven by a favourable interaction between the different liquid crystal groups. If an odd-membered dimer possesses sufficient molecular curvature, then the twist-bend nematic phase may be seen in which spontaneous chirality is observed for a system consisting of achiral molecules. Combining the empirical relationships developed for smectogenic dimers, and more recently for twist-bend nematogenic dimers, we show how dimers were designed to show the new twist-bend, heliconical smectic phases. These have been designated SmC<sub>TB</sub> phases in which the director is tilted with respect to the layer plane, and the tilt direction describes a helix on passing between layers. We describe three variants of the SmC<sub>TB</sub> phase, and in each the origin of the symmetry breaking is attributed to the anomalously low-bend elastic constant arising from the bent molecular structures. |
| first_indexed | 2024-03-10T00:20:45Z |
| format | Article |
| id | doaj.art-4f148bedd7e14467b7a1158fce0be86a |
| institution | Directory Open Access Journal |
| issn | 2073-4352 |
| language | English |
| last_indexed | 2024-03-10T00:20:45Z |
| publishDate | 2022-09-01 |
| publisher | MDPI AG |
| record_format | Article |
| series | Crystals |
| spelling | doaj.art-4f148bedd7e14467b7a1158fce0be86a2023-11-23T15:43:52ZengMDPI AGCrystals2073-43522022-09-01129124510.3390/cryst12091245Liquid Crystal Dimers and Smectic Phases from the Intercalated to the Twist-BendCorrie T. Imrie0Rebecca Walker1John M. D. Storey2Ewa Gorecka3Damian Pociecha4Department of Chemistry, School of Natural and Computing Sciences, University of Aberdeen, Scotland AB24 3UE, UKDepartment of Chemistry, School of Natural and Computing Sciences, University of Aberdeen, Scotland AB24 3UE, UKDepartment of Chemistry, School of Natural and Computing Sciences, University of Aberdeen, Scotland AB24 3UE, UKFaculty of Chemistry, University of Warsaw, ul. Zwirki i Wigury 101, 02-089 Warsaw, PolandFaculty of Chemistry, University of Warsaw, ul. Zwirki i Wigury 101, 02-089 Warsaw, PolandIn this review we consider the relationships between molecular structure and the tendency of liquid crystal dimers to exhibit smectic phases, and show how our application of these led to the recent discovery of the twist-bend, heliconical smectic phases. Liquid crystal dimers consist of molecules containing two mesogenic groups linked through a flexible spacer, and even- and odd-membered dimers differ in terms of their average molecular shapes. The former tend to be linear whereas the latter are bent, and this difference in shape drives very different smectic behaviour. For symmetric dimers, in which the two mesogenic groups are identical, smectic phase formation may be understood in terms of a microphase separation into distinct sublayers consisting of terminal chains, mesogenic units and spacers, and monolayer smectic phases are observed. By contrast, intercalated smectic phases were discovered for nonsymmetric dimers in which the two mesogenic units differ. In these phases, the ratio of the layer spacing to the molecular length is typically around 0.5 indicating that unlike segments of the molecules overlap. The formation of intercalated phases is driven by a favourable interaction between the different liquid crystal groups. If an odd-membered dimer possesses sufficient molecular curvature, then the twist-bend nematic phase may be seen in which spontaneous chirality is observed for a system consisting of achiral molecules. Combining the empirical relationships developed for smectogenic dimers, and more recently for twist-bend nematogenic dimers, we show how dimers were designed to show the new twist-bend, heliconical smectic phases. These have been designated SmC<sub>TB</sub> phases in which the director is tilted with respect to the layer plane, and the tilt direction describes a helix on passing between layers. We describe three variants of the SmC<sub>TB</sub> phase, and in each the origin of the symmetry breaking is attributed to the anomalously low-bend elastic constant arising from the bent molecular structures.https://www.mdpi.com/2073-4352/12/9/1245liquid crystal dimersintercalatedinterdigitatedtwist-bend nematictwist-bend smecticchirality |
| spellingShingle | Corrie T. Imrie Rebecca Walker John M. D. Storey Ewa Gorecka Damian Pociecha Liquid Crystal Dimers and Smectic Phases from the Intercalated to the Twist-Bend Crystals liquid crystal dimers intercalated interdigitated twist-bend nematic twist-bend smectic chirality |
| title | Liquid Crystal Dimers and Smectic Phases from the Intercalated to the Twist-Bend |
| title_full | Liquid Crystal Dimers and Smectic Phases from the Intercalated to the Twist-Bend |
| title_fullStr | Liquid Crystal Dimers and Smectic Phases from the Intercalated to the Twist-Bend |
| title_full_unstemmed | Liquid Crystal Dimers and Smectic Phases from the Intercalated to the Twist-Bend |
| title_short | Liquid Crystal Dimers and Smectic Phases from the Intercalated to the Twist-Bend |
| title_sort | liquid crystal dimers and smectic phases from the intercalated to the twist bend |
| topic | liquid crystal dimers intercalated interdigitated twist-bend nematic twist-bend smectic chirality |
| url | https://www.mdpi.com/2073-4352/12/9/1245 |
| work_keys_str_mv | AT corrietimrie liquidcrystaldimersandsmecticphasesfromtheintercalatedtothetwistbend AT rebeccawalker liquidcrystaldimersandsmecticphasesfromtheintercalatedtothetwistbend AT johnmdstorey liquidcrystaldimersandsmecticphasesfromtheintercalatedtothetwistbend AT ewagorecka liquidcrystaldimersandsmecticphasesfromtheintercalatedtothetwistbend AT damianpociecha liquidcrystaldimersandsmecticphasesfromtheintercalatedtothetwistbend |