| Autor: |
Zhang RB; Department of Materials Science and Engineering, University of Sheffield, Sheffield S1 3Jd, UK. Pandagreater@gmail.com., Grunwald MA; Institut für Organische Chemie, Universität Stuttgart, D-70569 Stuttgart, Germany., Zeng XB; Department of Materials Science and Engineering, University of Sheffield, Sheffield S1 3Jd, UK. Pandagreater@gmail.com., Laschat S; Institut für Organische Chemie, Universität Stuttgart, D-70569 Stuttgart, Germany., Cammidge AN; School of Chemistry, University of East Anglia, Norwich, UK., Ungar G; Shaanxi International Research Center for Soft Materials, Xi'an Jiaotong University, Xi'an 710049, China. g.ungar@xjtu.edu.cn. |
| Abstrakt: |
Confined in a cylindrical pore with homeotropic anchoring condition, the hexagonal columnar phase of discotic liquid crystals can form a "log-pile" configuration, in which the columns are perpendicular to the long axis of the pore. However, the {100} planes of the hexagonal lattice can orient either parallel (termed (100) ‖ orientation) or perpendicular ((100) ⊥ ) to pore axis. Here we experimentally show that the (100) ‖ orientation is found in narrower cylindrical pores, and the (100) ‖ -(100) ⊥ transition can be controlled by engineering the structure of the molecules. The (100) ‖ orientation is destroyed in asymmetric discotics hepta(heptenyloxy)triphenylene (SATO7); replacing the oxygen linkage in hexa(hexyloxy)triphenylene (HATO6) by sulphur (HATS6) improves the (100) ‖ orientation in small pores; adding a perfluorooctyl end to each alkyl chain of HATO6 (HATO6F8) moves the (100) ‖ -(100) ⊥ transition to larger pores. We have provided a semi-quantitative explanation of the experimental observations, and discussed them in the context of previous findings on related materials in a wider pore size range from 60 nm to 100 μm. This allows us to produce a comprehensive picture of confined columnar liquid crystals whose applications critically depend on our ability to align them. |
