Synthesis, thermal, dielectric and electro-optic properties of new series of fluorinated hydrogen-bonded liquid crystals

Mouna Derbali (1) , Taoufik Soltani (1) , Ahlem Guesmi (2) , Naoufel Ben Hamadi (2) , Erwann Jeanneau (3) , Yves Chevalier (4)

1 UTM - Université de Tunis El Manar
2 IMSIU - Imam Mohammad Ibn Saud Islamic University
3 UCBL FS - Université Claude Bernard Lyon 1 - Faculté des sciences
4 LAGEPP - Laboratoire d'automatique, de génie des procédés et de génie pharmaceutique

Two series of hydrogen-bonded liquid crystals (HBLC) were investigated: 4-alkoxy-2,3-difluorobenzoic acids (nOBAFF) with alkoxy chain lengths of n = 7–12 carbon atoms and mixtures of nOBAFF and 4-octyloxybenzoic acid (8OBA). Their phase behavior has been established using differential scanning calorimetry, polarized optical microscopy and X-ray diffraction. At variance with non-fluorinated and monofluorinated homologues, the difluorinated nOBAFF compounds only form SmA and SmC liquid crystalline phases. An additional nematic phase is obtained upon mixing nOBAFF and 8OBA, showing the sequence: Isotropic liquid–Nematic–SmA–SmC–crystalline solid upon cooling from the isotropic phase. All the transition temperatures decrease with increasing alkoxy chain length of nOBAFF, which reveals a decrease of order parameter for longer chains. The dielectric and electro-optic behaviors of the nematic phase of nOBAFF/8OBA mixtures reveal a decrease of the threshold voltage and response time upon increasing the alkyl chain length of nOBAFF

Mots clés: Hydrogen-bonded liquid crystal; Nematic phase; Smectic phases; Dielectric spectroscopy

Domaines: Matériaux; Chimie organique

Mouna Derbali, Taoufik Soltani, Ahlem Guesmi, Naoufel Ben Hamadi, Erwann Jeanneau, et al.. Synthesis, thermal, dielectric and electro-optic properties of new series of fluorinated hydrogen-bonded liquid crystals. Journal of Molecular Liquids, 2022, 367, pp.120510. ⟨10.1016/j.molliq.2022.120510⟩. ⟨hal-03821253⟩