meta-Cybotaxis and nematic biaxiality

Abstract

In 1970, two seemingly unrelated reports about nematic liquid crystals appeared in the scientific literature: at Kent State University, Adrian de Vries reported local smectic order in a nematic that he termed cybotactic, and at IBM, Marvin Freiser showed the possibility of a lower symmetry nematic that he named biaxial. These two discoveries are connected through consideration of the origins of spontaneous symmetry breaking, in particular, how broken symmetry within transient clusters permeating a nominally uniaxial nematic may lead to a biaxial nematic.

Keywords:

• biaxial nematic
• cybotactic
• bent-core mesogen
• nematic

Acknowledgements

This work was supported by NSF grant DMR-9971143. Conversations with Demetri Photinos, Geoffrey Luckhurst, Lou Madsen, and Theo Dingemans helped me formulate the ideas expressed herein.

Notes

1.  Note that Saupe's 1968 review predates the experimental report of discotics and the rediscovery of bent-core liquid crystals and was, therefore, restricted to rod-shaped molecules, so-called calamitic mesogens. Apart from the sign of the birefringence, generally negative for disc-shaped molecules and positive for calamitics, both of those classes of nematics are characterised by long-range orientational order without translational order; the short axes are aligned along n in the case of discotic nematics.

2.  Marvin Freiser understood the difficulty of realising the molecular biaxial nematic and concluded his 1970 publication [7] as follows: “Such a sequence of transitions [N_U → N_B] is consistent with the symmetry of the molecules in real nematic liquids and should therefore occur. However, crystallization of the medium or the onset of a smectic phase may intervene.”