Helical nanofilaments of bent-core liquid crystals with a second twist

Abstract

The B4 phase of bent-core liquid crystals has been shown to be an assembly of twisted layers stacked to form helical nanofilaments. Interestingly, some of them have structural colours that cannot be explained by the nanofilaments alone. Here cryogenic-transmission electron microscopy observations on 40-120 nm films of four bent-core liquid crystal materials show that the filaments are present even in contact with a carbon substrate with only minor deformation, thus representing bulk properties. We find that the subsequent arrays of nanofilaments are not parallel to each other, but rotate by an angle of 35-40°with respect to each other. This doubly twisted structure can explain the structural colour. Being principally different from the packing of molecules in the twist grain boundary and blue phases, the double-twist structure of helical nanofilaments expands the rich word of nanostructured organic materials.

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

“…In calculating this, we utilised that ΔI = I ¼ 1 À e ÀQ:Δh , where Q is the total elastic scattering cross section. [25] For all of our samples, ΔI/I < 0.3, so ΔI=I % Q:Δh. Previous measurements on similar layered bent-core materials with presumably similar Q values provided that ΔI=I % 0:25 corresponds to about Δh~30 nm.…”

“…Previous measurements on similar layered bent-core materials with presumably similar Q values provided that ΔI=I % 0:25 corresponds to about Δh~30 nm. [25] 3. Discussion These cryo-TEM results show very different behaviour from that we observed previously on an other B7-type material, [22] where only the a-spacing (with smaller value than in bulk) was visible.…”

“…Previous studies on other thermotropic bent-core LC films carried out with this instrument demonstrated the possibility to visualise smectic layers with resolution better than 0.7 nm. [22,[24][25][26] The LC samples were dissolved in chloroform, and the solution was dispersed on a TEM grid coated with plasma-treated continuous carbon film. After evaporation of the chloroform, the thickness of the LC films was between 50 and 100 nm.…”

Perspective: Geometrically frustrated assemblies

“…9(a)), whose width and thickness (stack height) are finite and in the range of 10s of nm, while the length of nanoribbons is unlimited. 121,122 The self-limitation of width can be understood by considering the "high chirality" limit 123 where K 2 is sufficiently large to lock the director into the preferred cholesteric twist, n(z) = cos(q 0 z), sin(q 0 z), 0 , where z is the pitch axis of the helicoid andŵ = − sin(q 0 z), cos(q 0 z), 0) is the direction along its width. While it is possible to align the director and the normal along the central pitch axis of helicoid, frustration prevents their global alignment and N − n ≃ q 0 x wẑ , where x w ∈ [−w/2, +w/2] is the position along the width.…”

Geometric phase ando-mode blueshift in a chiral anisotropic medium inside a Fabry-Pérot cavity

“…This generalization is necessary in media such as a cholesteric LC [39][40][41][42] and a TN cell of small thickness and other media with a sharp spatial variation of dielectric characteristics at the wavelength scale [43][44][45][46]. However, Jones formalism gives a good approximation when the thickness of the TN cell is several times larger than the wavelength and the dielectric constant varies smoothly.…”