Columnar discotics in confined geometries

• Published in: Liquid crystals Vol. 27; no. 5; pp. 643 - 648
• Main Authors: Kopitzke, J., Wendorff, J. H., Glusen, B.
• Format: Journal Article
• Language: English
• Published: Taylor & Francis Group 01.05.2000
• ISSN: 0267-8292; 1366-5855
• DOI: 10.1080/026782900202499

The influence of geometric confinement on the state of order and on the glass relaxation process was investigated for a triphenylene derivative able to display a highly ordered plastic columnar phase in the bulk. The compound was incorporated into porous glasses - characterized by a narrow size distribution - with average pore diameters of 20, 7.5, 5 and 2.5 nm. The X-ray diagrams revealed the presence of a hexagonal order, yet the lattice spacing is significantly reduced with decreasing pore size and the reflections become broad. The X-ray doublet reflection, superimposed on the halo which is characteristic for the bulk plastic columnar phase, is absent in all cases. It is replaced by a single broad intracolumnar reflection which indicates that the confinement destabilizes the plastic phase in favour of the hexagonal ordered phase. A further observation is that the intracolumnar correlation length is reduced with decreasing pore size. The confinement was furthermore found to cause a transition from a strong glass (bulk material) to a fragile glass former, obviously induced by the structural modification.