Uniaxial Orientation of Columnar Discotic Liquid Crystals

Abstract

The present paper explores the possibility of orienting columnar discotic liquid-crystalline (LC) materials and causing a uniaxial "in-plane" orientation of the columns along the orientation direction. The discotic LCs employed were based on 2-hydroxy-3,6,7,10,11-penta-(1-butoxy)triphenylene, which was derivatized with 1-adamantenecarboxylic acid (Ada-PBT) and 10-undecenoic acid (ω-undecenoyl-PBT), respectively. As unequivocally shown by optical microscopy, uniaxial alignment of columnar Ada-PBT structures was readily achieved by spin-coating this material onto a poly(tetrafluoroethylene) orientation layer. Annealing of the films at temperatures at which the Ada-PBT was in its hexagonal plastic or hexagonal ordered mesophase slightly increased the degree of orientation. The optical absorption and photoluminescence spectra of oriented Ada-PBT films were significantly polarized, with absorption and emission dichroic ratios of 6.5 and 3, respectively. The optical anisotropy is unambiguously related to the uniaxial "in-plane" orientation of the cylindrical stacks of the LC molecules rather than an alignment of individual Ada-PBT molecules. Interestingly, this orientational behavior could not be mirrored when attempting to orient blend films of ultrahigh molecular weight polyethylene (UHMW-PE) and Ada-PBT or ω-undecenoyl-PBT by tensile deformation.

Homeotropic Alignment of Columnar Liquid Crystals in Open Films by Means of Surface Nanopatterning

“…Similar studies have been conducted on Ada-PBT that was in the glassy state produced by quenching from hexagonal columnar plastic or hexagonal columnar ordered phases. [22] Therefore, our temperature-dependent experiments revealing homeotropic columnar orientation on PTFE are, to the best of our knowledge, the first examples of such studies on Col h phases. The reasons for the homeotropic alignment of Col h phases could be different for the two systems described in the paper.…”

“…[21][22][23] However, a more detailed analysis of the literature data shows that the LC films studied previously were not in the Col h phase. For example, the films of TiOPc [21] or HBC-C8,2 [23] were in the crystalline state whereas the films of HBC-PhC12 were in the LC state but in a mesophase different from Col h (Col r phase at room temperature [24] ).…”

Liquid Crystals for Charge Transport, Luminescence, and Photonics

“…Uniaxial orientation of a triphenylene-based discotic LC, which is a glass at room temperature, was obtained by spin-coating onto an oriented PTFE film on glass. [84] Improved ordering was obtained by annealing above the T g .…”

A hexagonal columnar packing structure of C7 symmetric supramolecules: a superstructure of a 2:3 complex of heptakis‐(6‐O‐tert‐butyldimethylsilyl)‐β‐cyclodextrin and ethyl acetate

“…In general, disk or cylinder-shaped molecules are organized into the columnar superstructure in crystal (or liquid crystal) [9][10][11][12][13][14][15]. However, β-cyclodextrin (β-CD) and its derivatives, typical cylindrical molecules widely used as clathrate hosts [16][17][18][19][20][21], do not generate a hexagonal columnar structure in crystal.…”