Surface alignment, anchoring transitions, optical properties, and topological defects in the thermotropic nematic phase of organo-siloxane tetrapodes

Kim, Young-Ki; Senyuk, Bohdan; Shin, Sung-Tae; Kohlmeier, Alexandra; Mehl, Georg H.; Lavrentovich, Oleg D.

Abstract

We address the status of oxadiazole mesogens, C7 and C12, reported to show the biaxial nematic phase, by exploring material aspects (chemical stability, surface anchoring, optical and dielectric properties, topological defects) linked to the type of nematic order. We demonstrate that the isogyres splitting in conoscopic patterns of homeotropic state depends on sample thickness and is associated with variations of molecular tilt along the normal to substrates. We observe isolated topological point defects (boojums and hedgehogs), as well as nonsingular “escaped” disclinations pertinent only to the uniaxial nematic order. Our conclusion is that C7 and C12 feature only a uniaxial nematic phase and the apparent biaxiality is caused by surface effects.

Citation

Kim, Y.-K., Senyuk, B., Shin, S.-T., Kohlmeier, A., Mehl, G. H., & Lavrentovich, O. D. (2014). Surface alignment, anchoring transitions, optical properties, and topological defects in the thermotropic nematic phase of organo-siloxane tetrapodes. Molecular crystals and liquid crystals, 540(1), 20-41. https://doi.org/10.1039/C3SM52249K

• Journal Article Type: Article
• Acceptance Date: Nov 1, 2013
• Online Publication Date: Nov 5, 2013
• Publication Date: Jan 1, 2014
• Deposit Date: Dec 24, 2015
• Publicly Available Date: Nov 23, 2017
• Journal: Molecular crystals and liquid crystals
• Print ISSN: 1542-1406
• Publisher: Taylor and Francis
• Peer Reviewed: Peer Reviewed
• Volume: 540
• Issue: 1
• Pages: 20-41
• DOI: https://doi.org/10.1039/C3SM52249K
• Keywords: Thermotropic nematic phase
• Public URL: https://hull-repository.worktribe.com/output/383630
• Publisher URL: http://www.tandfonline.com/doi/abs/10.1080/15421406.2011.568324
• Additional Information: This is an author's accepted manuscript of an article published in Molecular crystals and liquid crystals, 2011, v.540 issue 1.
• Contract Date: Nov 23, 2017