||Hockey stick mesogens were constructed by attaching flexible chains laterally (at meta-position) to a rod-like mesogenic core—3-hydroxyphenyl 4’-alkyloxy biphenyl-4-carboxylate. While the para-positioned chain were varied from octyloxy to dodecyloxy in length, the meta-positioned chains, hexyloxy and octyloxy (series III and IV), were replaced with nonafluorohexyloxy and tridecafluorooctyloxy chains (series I and II), respectively. The obtained mesogens and mesophases were studied with optical polarizing microscopy (OPM), differential scanning calorimetry (DSC), X-ray diffraction (XRD), and electric field effect.
Mesophases of smectic A (SmA), smectic C (SmC) and anticlinic smectic Ca (SmCa) were observed for the non-fluoro-derivatives, and only SmA and SmC were observed for the fluoro-derivatives. The OPM observation showed that the textures of SmA and SmC resemble those of rod-like mesogens, but occasionally with 2-brush defects in the schlieren textures of SmC. For the SmCa phase, the schlieren texture was dominated with 2-brush defects and the focal conic fans were overlapped with equal-distant parallel lines. The DSC study showed that the phase transitions of SmA-SmC and SmC-SmCa were all weakly first-order. Preliminary XRD results showed that these smectic phases were monolayer structure, and only very small layer contraction across the SmA-SmC transition was observed.
Elongated domains were observed for SmC and SmCa phases of these compounds in liquid crystal cell with surfaces treated for parallel alignments, 2μ thickness. The neighboring domains exchanged their dark and light appearance when the sample was rotated to opposite direction, but remained unchanged with inversion of the polarity of electric field. The SmCa phase exhibited similar behavior except that the parallel lines across the domains would gradually disappear with increasing field strength. The polarization of these smectic phases remain to be studied.