The interplay between spatial and heliconical bond order in twist-bend nematic materials*

The nanostructure of two novel sulfur containing dimer materials have been investigated
experimentally by hard and by resonant tender X-ray scattering techniques. We find that below the nematic (N) to NTB transition the positional correlations drop significantly, while the bond-order correlations increase from zero to about 60 nm. The temperature dependences of the heliconical pitch show stronger variation neat the N-NTB transition that the CBnCB-type dimers. The heliconical pitch is observable even in the upper 3-4°C range of the underlying smectic phase. The coexistence of the smectic order and the heliconical order indicates a SmCTB -type phase where the rigid units of the dimers are tilted with respect to the layer normal to allow for the bending of the dimers, but the tilt direction rotates following the heliconical order.