Surface Order in Thin Films of Self-Assembled Columnar Liquid Crystals

Abstract

The way in which alignment of hexagonal columnar mesophases depends on molecular structure, film thickness, and surface interactions is investigated. Homeotropic orientation of tapered nonpolymeric and polymeric amphiphilic columnar molecules occurs most readily on carbon substrates. The planar alignment of asymmetric dendrimers is favored on a water surface but is not possible for a symmetric dendrimer. For the polymeric material, film thickness has a significant influence on the morphology. Thick films align homeotropically, but films that are only a few column diameters in thickness are planar, and their thickness is quantized. Because they must contain an integral number of layers of cylinders, the resulting morphology is terraced.

Columnar Mesophases Based on Zinc Chlorophyll Derivatives Functionalized with Peripheral Dendron Wedges

“…[38] X-ray and STM results have been compared for some LC compounds and similarities as well as differences for the lattice parameters and unit cells obtained from these two methods have been reported. [37a-c] The area of the 2D lattices of the columnar structures obtained from powder XRD and the cyclic structures observed by STM for ZnChl 1 are compared in order to verify whether similar molecular arrangement prevails within the column stratum of the LC phases as on the surface.…”

Alkyl Tail Length Dependence of Structures in a Series of Symmetrically Tapered Bisamides Exhibiting Self‐Assembled Supramolecular Columnar Phases

“…[7] In addition to the traditional columnar phases constructed with discogenic molecules with flexible tails, novel discotic LC systems have also been made from different building blocks such as chiral molecules, [8] inverted molecules, [9] or even dendrimers. [10] One of the new ideas in columnar discotic LCs is the development of self-assembly through noncovalent interactions. In these systems, columnar LC phases are not formed via discotic molecules or main-chain macromolecules, but rather by supramolecular discs as building blocks generated from rod-shaped [11] or half disc-shaped [12] molecules through intra/intermolecular noncovalent interactions.…”

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

“…Although it is quite usual to have homeotropic alignment of LCs squeezed between two substrates, a general strategy for achieving such an alignment in open films is still lacking, and studies of LC alignment in this geometry are very scarce to date. [6][7][8] Generally, the orientation of columns in open films is believed to result from competition between the homeotropic and homogeneous, or inplane, alignment (top panel of Fig. 1) due to the difference in the surface tensions between air/LC and LC/substrate.…”

“…1) due to the difference in the surface tensions between air/LC and LC/substrate. [7] It was found that such an alignment is governed by the substrate surface energy, [8] chemical structure of the molecules, [9][10][11][12] and/or the sample thermal history such as cooling rate [13] or annealing temperature and time. Recently, it was observed that homeotropic alignment in films confined between two surfaces could be facilitated by irradiating the sample with circularly polarized infrared light at the wavelength corresponding to vibration of a chosen chemical bond of the LC molecule.…”