Nanoscale structures of polarisation-modulated bent-core materials in thin films

Abstract

We present small angle X-ray and cryogenic transmission electron microscopy (cryo-TEM) studies of three nitrosubstituted (n-OPIMB-NO 2 , n = 7, 9 and16) bent-core liquid crystals (LCs) that form peculiar optical patterns known as B7 textures. Small angle X-ray scattering studies show two periodicities between a~3.4-4.7 nm and b X~9 -16 nm. Cryo-TEM images of about 100 nm thick films do not show the a-periodicity, but only periodicities b T that are about 1 nm smaller than b X measured in bulk by X-ray. Additionally, an intensity modulation with a period c~100-200 nm is observed. These observations can be explained by a B1-type structure, where there are half-layer step discontinuities at the boundaries of the splay domains, and where the molecules are everywhere normal to the substrate.

Rupture and recoil of bent-core liquid crystal filaments

“…This is consistent with the smaller b values of N7 (b B 9 nm for N7 and b B 16 nm for N16 as seen in Fig. 1(a)), meaning more areas with lower packing densities 30 where the molecules can be pushed between layers. (ii) The viscosities at higher temperatures appear to be lower.…”

“…For example, at 150 1C, they are a = 3.43 nm, b = 9.0 nm, and f = 851 for N7, and a = 4.7 nm, b = 15.6 nm, and f = 81.61 for N16. Recent cryo-TEM experiments show that these materials have a strongly modulated layer structure, where there are half layer step discontinuities at the boundaries of the splay domains, 30 which resemble columnar structures. 31,32 A motorized and temperature-controlled setup [ Fig.…”

B7 Liquid Crystal Filament Growth in Presence of Carbon Nanotubes

“…At least seven principle bent‐core liquid crystalline phases have been discovered so far, of which the B7 phase is probably the most intriguing and most complicated at the same time. On cooling from the isotropic melt, a wealth of structural features can be identified by polarizing microscopic observation, such as the formation of left‐and right‐handed helices, and single‐ and doubly‐twisted ribbons, similar to normal and super‐twisted telephone cords, but also domains with equidistant striped patterns which indicate some twisted, or undulated structures ,…”