Abstract
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 crys-talline 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. (c) 2022 Elsevier B.V. All rights reserved.