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Title: What stabilizes the twist-bend nematic phase
Plain: Bent-shaped molecules can form a nematic whose alignment spirals with a pitch of only about 100 Angstrom, the twist-bend nematic. Whether it forms because bending becomes energetically favourable or because of hidden polar order is disputed.
Precise: The twist-bend nematic $N_{\mathrm{TB}}$ (heliconical director, pitch about $8e-7\ \text{to}\ 1e-6\,\mathrm{cm}$ in CB7CB) was predicted from a negative bend elastic constant $K_{33} < 0$ and alternatively explained through coupling to local polar order or flexoelectricity. Determine which mechanism stabilizes $N_{\mathrm{TB}}$ and derive its coarse-grained elasticity (whether it behaves as a pseudo-layered smectic) from measured elastic constants and structure.
Settled by: Measurement of the elastic constants and polar order through the $N$ to $N_{\mathrm{TB}}$ transition, compared with predictions of the competing theories.
Kind: phenomenon
Answer type: mechanism
References: (empty)
Literature status: contested
Status note: (empty)
Posed since: 2013