Biaxial nematics: symmetries, order domains and field-induced phase transitions^†

^†This paper is based on an invited lecture presented at the 22nd International Liquid Crystal Conference (Jeju, Korea, 2008).

Abstract

We studied the symmetry and spatial uniformity of the orientational order of the biaxial nematic phase in the light of recent experimental observations of phase biaxiality in thermotropic bent-core and calamitic-tetramer nematics. Evidence is presented supporting monoclinic symmetry, instead of the usually assumed orthorhombic symmetry. The use of deuterium nuclear magnetic resonance to differentiate between the possible symmetries is described. The spatial aspects of biaxial order are presented in the context of the cluster model, wherein macroscopic biaxiality can result from the field-induced alignment of biaxial and possibly polar domains. The implications of different symmetries on the alignment of biaxial nematics and on the measurements of biaxial order are discussed in conjunction with the microdomain structure of the biaxial phase.

Keywords:

• biaxial nematics
• phase symmetries
• nuclear magnetic resonance
• biaxial order domains
• Landau-de Gennes theory

Acknowledgements

The research leading to these results has received funding from the European Community's Seventh Frameworth programme (FP7/2007–2013) under grant agreement n° 216025 (Biaxial Nematic Devices).

Notes

^†This paper is based on an invited lecture presented at the 22nd International Liquid Crystal Conference (Jeju, Korea, 2008).