Morphological phase behaviour under pressure of polycatenar mesogens with a perfluorinated moiety |
| |
Authors: | Yoji Maeda Etsushi Nishikawa Hiroshi Yokoyama |
| |
Affiliation: | a Liquid Crystal Nanosystem Project, SORST, Japan Science and Technology Agency, Tsukuba, Ibaraki 300-2635, Japan |
| |
Abstract: | Two polycatenar materials composed of a four-aromatic-ring core with a perfluorinated moiety attached in one terminal position through either butylene- or pentylene spacer groups, and three tetradecyloxy chains at the other end (abbreviated as 14PC4F and 14PC5F), were investigated to study the effect of pressure on the phase transition behaviour. A polarizing optical microscope equipped with a high pressure optical hot stage, was used for the purpose. The T vs. P phase diagrams of 14PC4F and 14PC5F were constructed in the pressure region up to 100 MPa. 14PC4F showed the stable crystal (Cr1)-columnar tetragonal (Coltet)-smectic A (SmA)-columnar hexagonal (Colh)-isoropic liquid (I) phase transition sequence under all pressures. 14PC5F exhibited the phase sequence metastable crystal (Cr2)-cubic (Cub)-Coltet-SmA-I in a melt-cooled sample on heating under pressure. But when the melt-cooled Cr2 sample was annealed at 52-54°C for 2-3 h, the stable crystal (Cr1) was formed slowly, giving a stable Cr1-Cub-Coltet-SmA-I phase sequence. The temperature region of the stable cubic phase broadened with increasing pressure. Furthermore a new mesophase of 14PC5F was pressure-induced between the I and SmA phases on cooling at pressures above about 16 MPa. Since the monotropic mesophase exhibited a texture very similar to that of the high temperature Colh phase of 14PC4F with planar orientation, the new phase was assigned at a high temperature columnar hexagonal phase of 14PC5F. |
| |
Keywords: | |
本文献已被 InformaWorld 等数据库收录! |
|