The twist bend nematic: a case of mistaken identity

ABSTRACT

We review the physics underlying Meyer’s conjecture of how macroscopic-scale twist and bend conspire within the Frank-Oseen elasticity theory of nematics to create a heliconical arrangement of the uniaxial, apolar nematic director, the so-called ‘twist bend nematic’ N_TB. We show that since 2011 a second, lower-temperature nematic phase observed in odd methylene-linked cyanobiphenyl dimers discovered by Toriumi and called N_X, has been incorrectly identified as N_TB. Moreover, as more quantitative data on the N_X emerged, Meyer’s simple prediction has been distorted to accommodate those findings. In fact, the molecular organisation in the N_X conforms to the N_PT phase, a polar, twisted arrangement of nonlinear mesogens advanced in 2016. The attributes of the N_PT are summarised and differentiated from those of the N_TB in an effort to contribute to a better understanding of the N_X phase and, equally important, to encourage researchers to continue to search for a liquid crystal that exhibits Meyer’s pioneering theoretical suggestion, namely that form-chirality can exist in simple nematics composed of achiral molecules.

Graphical Abstract

KEYWORDS:

• Twist bend nematic
• polar twisted nematic

Disclosure statement

No potential conflict of interest was reported by the author(s).