The columnar phase is a type of mesophase where molecules form cylindrical stacks acting as mesogens. Initially known as discotic liquid crystals due to their disc-shaped units, recent discoveries include columnar liquid crystals made from various molecular shapes. These materials, a subclass of liquid crystals, represent a unique state of matter with ordered, one-dimensional stacking. Takuzo Aida and colleagues have developed cyclic peptides that self-assemble into polar columnar structures, capable of being aligned uniformly over large areas using an electric field, highlighting potential applications in advanced functional materials.
Classes
Columnar liquid crystals are grouped by their structural order and the ways of packing of the columns. Nematic columnar liquid crystals have no long-range order and are less organized than other columnar liquid crystals. Other columnar phases with long-range order are classified by their two-dimensional lattices: hexagonal, tetragonal, rectangular, and oblique phases.
The discotic nematic phase includes nematic liquid crystals composed of flat-shaped discotic molecules without long-range order. In this phase, molecules do not form specific columnar assemblies but only float with their short axes in parallel to the director (a unit vector which defines the liquid-crystalline alignment and order).
Current topics of interest
The first discotic liquid crystal was found in 1977 by the Indian researcher Sivaramakrishna Chandrasekhar. This molecule has one central benzene ring surrounded by six alkyl chains. Since then, a large number of discoid mesogenic compounds have been discovered in which triphenylene, porphyrin, phthalocyanine, coronene, and other aromatic molecules are involved. The typical columnar liquid-crystalline molecules have a pi-electron-rich aromatic core attached by flexible alkyl chains. This structure is attracting particular attention for potential molecular electronics in which aromatic parts transport electrons or holes and alkyl chains act as insulating parts. The advantages of liquid-crystalline conductors are their anisotropy, processibility, and self-healing characteristics for structural defects.3
- David Dunmur & Tim Sluckin (2011) Soap, Science, and Flat-screen TVs: a history of liquid crystals, pp 258–62, Oxford University Press ISBN 978-0-19-954940-5 .
References
Lin, Lei (Lam, Lui) (1987). "Bowlic liquid crytals". Mol. Cryst. Liq. Cryst 146: 41-54. ↩
Kohei Sato, Yoshimitsu Itoh, and Takuzo Aida http://pubs.acs.org/doi/abs/10.1021/ja203894r http://pubs.acs.org/doi/abs/10.1021/ja203894r ↩
S. Chandrasekhar, B. K. Sadashiva and K. A. Suresh,"Liquid crystals of disc-like molecules", Pramana, 1977, 9 471. ↩