Insights into Biaxial Ordering of Bent-Core Nematics: X-Ray Diffraction Evidence

Abstract

Recently we have reported the first X-ray diffraction evidence of biaxial order in the fluid cybotactic nematic phase of a pair of trimethylated bent-core mesogens. This evidence is based on the splitting of the wide-angle diffuse scattering in the plane normal to the nematic director. The additional experimental data presented here provide further insights into this unprecedented behavior observed over the entire nematic phase. Although we could not determine the spatial extent of biaxial order-intracluster or intercluster-our observations reveal an enhanced biaxial orientational correlation in the transverse molecular packing, possibly reflecting stronger anisotropic interactions between nearest-neighbor mesogens.

The effects of lateral halogen substituents on the low-temperature cybotactic nematic phase in oxadiazole based bent-core liquid crystals

“…In the wake of the recent observation of a splitting in the wide-angle XRD diffuse feature of trimethylated BCM, [65,66] we performed additional wideangle measurements on the chloro derivative. Selected patterns taken on cooling under magnetic field are shown in Figure 9(a)-(c).…”

“…[63][64][65][66][67] This has led to considerably lower transition temperatures compared to the non-methylated analogues; derivatives with three lateral methyl groups supercool to room temperature in the nematic phase ( Figure 1) and XRD studies indicate the presence of cybotactic clusters. In the case of the compound shown below, OC4 2MePh(mono3MeODBP), the nematic phase persists at room temperature for nearly 24 hours before crystallisation occurs.…”

“…This behaviour is only present in the trimethylated derivatives that supercool in the nematic phase to room temperature and is suggestive of enhanced biaxial ordering in the cybotactic clusters of such mesogens. [65,66] The effects of lateral polar groups (halogens, cyano, etc.) on BCM have also been investigated.…”

Validating an optimized GAFF force field for liquid crystals: TNI predictions for bent-core mesogens and the first atomistic predictions of a dark conglomerate phase

“…This has been attributed to a higher degree of local biaxial order, possibly due to the methyl substituents on the outer phenyl rings of the aromatic core. 3,33 Fig . 10a shows shows S 2 values calculated for the C4O-Ph-ODBP(trimethylated) mesogen as a function of decreasing temperature and averaged over the final 60 ns of production runs.…”

Search for microscopic and macroscopic biaxiality in the cybotactic nematic phase of new oxadiazole bent-core mesogens

“…on the length scale of the cybotactic cluster size) biaxial order in the N phase of a pair of trimethylated BCNs based on the 1,3,4-oxadiazole bisphenol (ODBP) mesogenic core (compounds 2, 3 in Fig. 1) [31,32]. This was inferred from the splitting of the wide-angle (WA) diffuse crescents in the XRD pattern of the N phase oriented in a magnetic field B orthogonal to the X-ray beam.…”