What stabilizes the twist-bend nematic phase?
In plain words
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 statement
The twist-bend nematic $N_{\mathrm{TB}}$ (heliconical director, pitch about $8 \times 10^{-7}\ \text{to}\ 10^{-6}\,\mathrm{cm}$ 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.
What would settle it
Measurement of the elastic constants and polar order through the $N$ to $N_{\mathrm{TB}}$ transition, compared with predictions of the competing theories.
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