K. Severing, K. Saalwächter.
A Biaxial Nematic Phase in a Thermotropic Liquid-Crystalline Side-Chain Polymer.
Phys. Rev. Lett. 92, 125501 (2004).
We report on variable-angle deuterium NMR measurements of nematic
liquid-crystalline side-chain polymers, where we have found proof of the
existence of a biaxial nematic phase in a system with side-on attachment of the
mesogenic group to the polymer backbone. This provides efficient coupling to the
polymer backbone and thus stabilizes the as yet elusive biaxial phase. The
experimental approach is validated on a uniaxial end-on nematic polymer, and the
reliability of the results is investigated in detail using two-dimensional
correlation spectra, providing information on director distribution effects.