Local Orientational Analysis of Helical Filaments and Nematic Director in a Nanoscale Phase Separation Composed of Rod-Like and Bent-Core Liquid Crystals Using Small- and Wide-Angle X-ray Microbeam Scattering

Abstract

We analyzed the local nanostructure in binary mixtures of rod- and bent-shaped molecules, n-pentyl-4-cyanobiphenyl (5CB) and 1,3-phenylene bis[4-(4-n-octyloxyphenyliminomethyl) benzoates] (P-8-OPIMB), respectively, using small- and wide-angle X-ray microbeam and macrobeam scattering. From the orientational X-ray scattering patterns, we concluded that the nematic director of 5CB is almost parallel to the smectic layers dominated by bent-core molecules in Bx. Moreover, we observed oriented small-angle diffraction peaks (about 300 Å), which is close to the spacing of 5-7 layers, and also consistent with the width of a helical nanofilament textures as observed by freeze-fracture transmission electron microscopy. The kinetics in B4 was also discussed based on the contact experimental method.

Chiral Superstructure Mesophases of Achiral Bent‐Shaped Molecules – Hierarchical Chirality Amplification and Physical Properties

“…Namely, they were prealigned and formed a thin film of 2.4 nm thick around the HNFs due to the short‐range interaction between them and the HNF surfaces. Regarding the <B4/N> phase, using dynamic light‐scattering, and then small‐ and wide‐angle X‐ray microbeam and macrobeam scatterings, Takanishi and co‐workers estimated the structure of the <B4/N> phase; 5CB‐rich domains with sizes of 450–600 nm are separated by HNFs consisting of 5–7 smectic layers, with thickness of about 300 Å. The obtained structure is in good accordance with the FFTEM observation, and the model suggested by CD measurements in the mixture of P‐8‐OPIMB and 5CB (Figure d), i.e., the nematic director aligns almost parallel to the grooves of the HNFs.…”

Diastereomeric liquid crystal domains at the mesoscale

“…1f), a result of the essentially complete phase separation of the mixture that reduces the possibility of significant chiral induction by the chiral guest molecules. Upon cooling, isotropic 7O.5* also exhibits an Iso* to Iso* surf transition at which an oriented LC layer on the HNF surfaces appears 54,55 at T E 70°C, as indicated optically by the sign change of Dn of the (R,R) domain and by DSC ( Supplementary Fig. 13).…”

“…For achiral guests the sign of Dn may or may not change at the Iso-N transition (the same in both L and R HNF domains of course), whereas for chiral guests at the Iso*-N* transition, Dn guest becomes distinctly different in the two domains with either the (L,R) or (R,R) changing sign at the transition, depending on the guest; smectic (Sm or Sm*)-the N-Sm transition of the bulk guest where the smectic contribution to Dn guest is increasingly negative with decreasing T and as large in magnitude as |Dn guest |B0.02. However, the nanoconfined guest/NOBOW HNF network systems consistently have an overall birefringence that is much smaller than that of the strongly birefringent, oriented bulk phases of the guest and/or NOBOW, in the range of 1 to 10% of the latter 55,56 . Such ratios require subwavelength orientational averaging of the guest LC optical anisotropy in which a significant fraction of the anisotropic molecular components have their high polarizability axes making a substantial angle y with the HNF.…”

“…3a,h). However, previous differential scanning calorimetry (DSC) and nuclear magnetic resonance (NMR) study 54,55 shows that the 8S5/ NOBOW and 8CB/NOBOW mixtures exhibit a nematic surface alignment by which the guest forms a several nanometer-thick oriented layer on the HNF surface at lower temperatures in the guest isotropic phase (at TB90°C for 8S5). This surface alignment is referred to as the isotropic surface-aligned state (Iso surf ) and is detectable in 8S5/NOBOW Dn data (Fig.…”

“…The failure of the guests to cause chiral induction is likely a consequence of both the high temperature at which the HNFs form in the melt, with the transition into the HNF phase occurring when the guests are isotropic, and of the extremely low solubility of the guests in the HNFs, making the guest-HNF interaction weak at high temperature. As the temperature is reduced, however, the chiral guest acquires local and then macroscopic orientational and positional liquid crystal order within the confines of the left-or right-handed domains of the HNF network 54,55 . This guest-host coupling then becomes significantly enhanced, with the guest increasingly influenced by the difference between the diastereomeric domains as manifested in distinctive thermo-optical orientation effects.…”