Orientation of chromonic liquid crystals by topographic linear channels: multi-stable alignment and tactoid structure

Abstract

We study the alignment behaviour of the chromonic liquid crystal phases of sunset yellow (SSY)/water, disodium cromoglycate (DSCG)/water and their mixtures when confined in cells by polymer films topographically imprinted with linear channels of 250 nm width, depth and spacing. A variety of novel alignment effects are generated by contact with such a patterned surface, as follows. Nematic DSCG and nematic SSY at low concentration and their nematic mixtures orient with the long axes of stacked chromonic aggregates on average parallel to the channels, that is, with the molecular planes normal to the channel axis. These oriented nematics exhibit isotropic/nematic tactoids aligned with their major axes along the channels. Two geometries of the tactoids, elliptic cylinder and rectangular cuboid with hemi cylindrical ends are observed. Additionally, a transition of DSCG tactoids from a three-dimensional (3D) director configuration to a two-dimensional one is observed when the tactoids on one surface of a cell touch the other surface of the cell. In SSY solutions of sufficiently high concentration, multi-stable alignment is found, including preferential in-plane orientation of the director parallel to, perpendicular to and 45 • rotated from the channels.

The 2013 Luckhurst-Samulski Prize

“…The final paper on the shortlist by Yi and Clark entitled Orientation of chromonic liquid crystals by topographic linear channels: multi-stable alignment and tactoid structure [23] describes an extensive study of how to control the alignment of chromonic liquid crystals and the effect of alignment layers on their structure. Chromonic liquid crystals have considerable application potential in a range of biological applications, but achieving their uniform alignment remains a demanding challenge.…”

Orthogonal Orientation of Chromonic Liquid Crystals by Rubbed Polyamide Films

“…[7,9,10] At high enough concentrations, the stacks have a local preferred orientation, called the director n(r), and form nematic phases. [17] Also reported are multi-stable alignments of the SSY stacks relative to topo-graphic line channels [18] and orthogonal orientation of stacks of Direct Blue 67 relative to orientation of azobenzene groups. [11,12] Nematic CLCs show schlieren textures when placed between crossed polarizers, due to spatially varying n fields of the aggregates of molecules or particles.…”

“…The molecules with nearly planar aromatic cores and sodium at their peripherals spontaneously assemble face-toface to form molecular stacks in water. Surfaces in contact with the CLCs are prepared by various methods, such as rubbing, [13,14] photo-alignment, [15,16] micro-/nano-fabrication, [17,18] oblique evaporation, [14,19] and shearing, [1,2] to obtain uniform optical textures and to enhance optoelectronic properties by promoting uniform n over macro-scaled areas of the CLCs. More information about CLCs, including their phases, structures, and applications can be found in recent review articles.…”

Aligning lyotropic liquid crystals with silicon oxides

“…Understanding lyotropic liquid crystal alignment configuration is essential, [5,6] and achieving a reproducible and reliable alignment becomes necessary for a number of applications related to biological materials that require the use of aqueous solutions, [7][8][9] especially in the context of chip-onglass. [10] The subject become even more pressing considering that even slight changes in the morphology and oxide content are known to drastically affect the hydrophilicity of the silicon oxide thin films, [11] which depending on the deposition technology employed can show moderate to high hydrophilicity with contact angles with pure water varying between almost 80 and less than 10 degrees. [12,13] 2.…”