Structure characterization of free-standing filaments drawn in the liquid crystal state

Abstract

Stable free-standing liquid filaments formed by some layered mesophases of bent-core mesogens are unique structures. Some of their physical properties have been analyzed in recent studies, but their microscopic structure and conditions for stability have still been unclear. We explore details of filament shapes and surface profiles of filaments drawn in liquid crystal phases of bent-core mesogens by AFM and SEM measurements, and we present a microscopic structure model. Conclusions on the stabilizing mechanisms are drawn. Qualitative differences in mechanical properties are found for different mesophases, even though the macroscopic appearance of the filaments is very similar.

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

“…[3] Examples include the twist-bend nematic phase [3][4][5] characterised by ambidextrous heliconical structure on 10-nm range without layering; the helical nanofilament phase [6] of 30-40 nm wide stack of twisted layers with about 100 nm half pitch and the so-called B7 material [7,8] that forms peculiar micrometre scale helical patterns and slender freely suspended filaments. [9][10][11][12][13][14] The amazing optical B7 textures attracted an intense research that lead to many important findings. [7][8][9]13,[15][16][17][18][19][20][21] Small angle X-ray scattering (SAXS) [7,16,19] studies revealed a number peaks [16,19] that can be indexed by a slightly oblique monoclinic 2D unit cell with a~3-5 nm and b~8-20 nm periodicities.…”

Microscopic structures of the B7phase: AFM and electron microscopy studies

“…However, in those studies single fibres (or whole bundles) did not form spontaneously, but were pulled mechanically between two supports. It has been shown that in contrast to the case of a columnar-type B 7 phase, the fibres of SmCP and PM-SmCP phases have cylindrical form [6].…”

“…Lamellar as well as columnar structures are encountered among the bent core ('banana') compounds. It has been shown that several mesophases such as SmCP (where P stands for polar), PM-SmCP (polarization modulated SmC) and B 7 can also form free-standing fibres [3][4][5][6]. Until now, microscopic textures associated with the B 7 phase ('B 7 texture') remained among the most mysterious patterns of the 'banana phases'.…”

Stability ofB7Fibers

“…In a number of experiments [3,4] it is observed that the crosssection of a fiber drawn in air is independent of its length. Assuming this the problem of describing a fiber is posed as a free boundary problem for the cross-section with its free energy per unit length based on the distinctive elastic (molecular packing) and electrostatic properties of bent core liquid crystals.…”