The University of Colorado campus with the famous Boulder Flatirons beyond, viewed from the Duane Physics building.

Thin freely suspended smectic film viewed in reflected light, with islands of greater thickness showing intereference colors.

Research Highlight: Experimental Determination of the Structure of the Exotic Twist-Bend Nematic Phase

Liquid crystal group members, in close collaboration with colleagues in the SMRC, have confirmed the existence and elucidated the structure of the elusive twist-bend nematic, a phase first proposed as a theoretical possibility by Meyer over 40 years ago and more recently suggested as a candidate for a mysterious chiral nematic phase with smectic-like textures observed in achiral dimeric mesogens by Luckhurst and co-workers. Although no smectic-like peaks were observed by x-ray scattering, freeze-fracture transmission electron microscopy revealed a periodic modulation of the tilted director, with a pitch comparable to the molecular length. This remarkable heliconical structure has also been observed in atomistic computer simulations and has now been confirmed experimentally in a number of bent dimer mesogens, as well as in rigid bent-core materials. Remarkably, while there are more than a dozen known smectic phases, this is only the fifth nematic phase identified in the last two centuries of liquid crystal research.

This work is described in D. Chen et al., PNAS 110, 15931–15936 (2013) and in D. Chen et al., Physical Review E 89, 022506 (2014).

The periodic, heliconical structure of the flexible dimer liquid crystal CB7CB is revealed by freeze-fracture transmission electron microscopy (top) and confirmed in atomistic computer simulations (bottom).