Distinct differences in the nanoscale behaviors of the twist–bend liquid crystal phase of a flexible linear trimer and homologous dimer

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 116; no. 22; pp. 10698 - 10704
• Main Authors: Tuchband, Michael R., Paterson, Daniel A., Salamończyk, Mirosław, Norman, Victoria A., Scarbrough, Alyssa N., Forsyth, Ewan, Garcia, Edgardo, Wang, Cheng, Storey, John M. D., Walba, David M., Sprunt, Samuel, Jákli, Antal, Zhu, Chenhui, Imrie, Corrie T., Clark, Noel A.
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 28.05.2019; National Academy of Sciences, Washington, DC (United States)
• Series: PNAS Plus
• Subjects: CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; Dimers; heliconical; Homology; liquid crystal; Liquid crystals; Oligomers; Physical Sciences; PNAS Plus; RSoXS; Soft x rays; Temperature dependence; trimer; Trimers; twist–bend nematic; X-ray scattering; RSoXS; heliconical; trimer; liquid crystal; twist–bend nematic
• DOI: 10.1073/pnas.1821372116
• ISSN: 0027-8424

We synthesized the liquid crystal dimer and trimer members of a series of flexible linear oligomers and characterized their microscopic and nanoscopic properties using resonant soft X-ray scattering and a number of other experimental techniques. On the microscopic scale, the twist–bend phases of the dimer and trimer appear essentially identical. However, while the liquid crystal dimer exhibits a temperature-dependent variation of its twist–bend helical pitch varying from 100 to 170 Å on heating, the trimer exhibits an essentially temperature-independent pitch of 66 Å, significantly shorter than those reported for other twist–bend forming materials in the literature. We attribute this to a specific combination of intrinsic conformational bend of the trimer molecules and a sterically favorable intercalation of the trimers over a commensurate fraction (two-thirds) of the molecular length. We develop a geometric model of the twist–bend phase for these materials with the molecules arranging into helical chain structures, and we fully determine their respective geometric parameters.