Resonant carbon K-edge soft x-ray scattering from lattice-free heliconical molecular ordering: soft dilative elasticity of the twist-bend liquid crystal phase

摘要

Resonant x-ray scattering shows that the bulk structure of the twist-bendliquid crystal phase, recently discovered in bent molecular dimers, has spatialperiodicity without electron density modulation, indicating a lattice-freeheliconical nematic precession of orientation that has helical glide symmetry.In situ study of the bulk helix texture for the dimer CB7CB shows anelastically-confined temperature-dependent minimum helix pitch, but aremarkable elastic softness of pitch in response to dilative stresses.Scattering from the helix is not detectable in the higher temperature nematicphase.