Comparative Study of the Optical and Dielectric Anisotropy of a Difluoroterphenyl Dimer and Trimer Forming Two Nematic Phases

Autor: Evangelia E. Zavvou, Chris Welch, Georg H. Mehl, Alexandros G. Vanakaras, Panagiota K. Karahaliou
Jazyk: angličtina
Rok vydání: 2024
Předmět:
Zdroj: Materials, Vol 17, Iss 11, p 2555 (2024)
Druh dokumentu: article
ISSN: 1996-1944
DOI: 10.3390/ma17112555
Popis: We present a comparative study of the optical and dielectric anisotropy of a laterally fluorinated liquid crystal dimer and its homologous trimer, both exhibiting two nematic phases. In the high-temperature nematic phase, both oligomers exhibit positive optical anisotropy with similar magnitude, which, however, is lower in comparison with the optical anisotropy of the monomer. In the same temperature range, the dielectric permittivity along and perpendicular to the nematic director, measured on magnetically aligned samples, reveals negative dielectric anisotropy for both oligomers, which saturates as the temperature approaches the N–N phase transition temperature. Comparison of the dielectric anisotropies of the oligomers with the corresponding anisotropy of the monomer indicates a systematic variation of its magnitude with the number of the linked mesogenic units. Results are compared with the corresponding anisotropies of the cyanobiphenyl dimers, the archetypal compounds with two nematic phases, and are discussed in terms of the dipolar structure of the mesogens and the dipolar correlations in their nematic phases.
Databáze: Directory of Open Access Journals
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