Addressing non‐idealities in NMR experiments on rotating liquid crystals

Abstract

Unequivocal evidence for a biaxial nematic phase in low‐molar‐mass calamitic thermotropic liquid crystals has been challenging to generate. Recently we provided NMR evidence that nonlinear calamitic mesogens based on the oxadiazole heterocycle exhibit a biaxial nematic phase (Phys. Rev. Lett., 2004, 92, 145505). Herein we probe the robustness of that claim by exploring potential variations of the director distribution from the ideal one that would apply to nematics rotated about an axis perpendicular to the spectrometer magnetic field. Moreover, we demonstrate that our methodology, when applied to the high temperature uniaxial nematic TBBA, yields a biaxial order parameter η = 0.0, thereby confirming the validity of our procedures. Our findings suggest that the original claim of biaxial order (η∼0.1) as reflected by probe molecule studies of oxadiazole mesogens is still valid.

Acknowledgement

We are indebted to Y. Galerne for drawing our attention to the general issue of inhomogeneous director distributions. This work was partially supported by NSF grant DMR‐9971143.

Notes

†. Note that we have slightly changed notation relative to our recent paper 11. J[i, z] has become J_i [z] to better follow standard notations. Also, we have corrected the fact that in this equation the Bessel functions are squared, which was omitted in equation (3) of that publication.