The synthesis and characterisation of two groups of nonsymmetric dimers, the 1-(4-cyanobiphenyl-4‘−yloxy)-ω-(4-butyl, 4-(1-methylpropyl) or 4-t-butylanilinebenzylidene-4’−oxy)alkanes, and the 1-(4-cyanobiphenyl-4‘−yl)-ω-(4-butyl, 4-(1-methylpropyl) or 4-t-butylanilinebenzylidene-4’−oxy)alkanes, are reported. For this purpose, many authors have used molecular modeling methods, mainly the density functional theory (DFT) or molecular dynamics simulations (MD) to analyze structural and conformational changes of the dimers. Current experimental results show that the formation of the N TB phase is very sensitive to changes in the shape of the molecules therefore, the key is to carefully define the relationship between the molecular parameters of the molecules and the occurrence of the modulated nematic phase. The structure of the NTB phase has primarily been studied using non-resonant (SAXS, WAXS) and resonant X-ray scattering as well as using polarized Raman, infrared and nuclear magnetic resonance spectroscopy (NMR). The twist-bend modulated nematic phase (NTB) has a helical structure with a pitch length of several nanometers. across the nematic (NTB)-SmCA transition shows the transition front, the rope texture of the NTB (left) is retained in the SmCA phase (right) with a significant change in birefringence (93.3 ☌) (d) rope-texture of the SmCA phase at 85 ☌ (e) striations visible in the focal-conic texture of the SmCA phase at 91.5 ☌ sandwiched between untreated glass (f) schlieren texture of the SmCA phase at 90 ☌ (g) six-brush dispirations in the schlieren texture of the SmCA phase at 91 ☌ (200x magnification) (h) two-brush defects in the schlieren texture of the SmCA phase at 93.1 ☌. We were unable to locate homeotropic or schlieren regions in the cell, and so we next studied CB8OFFFT by microscopy on untreated glass the nematic phase gave a characteristic schlieren texture (Supplementary Materials, Figure 1a) whereas the NTB phase afforded rope-like and blocky textures (Supplementary Materials, Figure 1b). observed a parabolic texture ( Figure 1b) along with a rope-like texture ( Figure 1c,1d), reminiscent of those exhibited by the twist-bend nematic phase, but exhibited by a smectic phase.
0 kommentar(er)
