New Nematic Ground States

Dr Richard Mandle from York University is coming to Leeds to present his research to the soft matter physics group.

Abstract:

The nematic liquid crystalline state is widely exploited in display devices and consists of molecules (or particles) with average orientational order but without positional organisation. The recent discovery of new nematic-like states of matter – so called modulated nematics – which are characterised by an additional periodic modulation of this orientational order, have attracted significant interest. In examples discovered to date the modulated local structure of these systems is driven by one or more of the Frank elastic constants being sufficiently small to enable spontaneous deformation of the nematic director.

In twist-bend nematic phase (NTB) the molecules tilt to form a helix with a pitch of a few nanometres. [1] In the first part of this talk I will discuss our work to elucidate the common molecular features which give rise to this unusual nematic state, the impact these changes have upon the properties of the NTB phase, and also the discovery of a new nematic ground state in certain chiral systems.

The second part of this talk focuses on the splay-nematic phase (NS), which is characterised by a periodic modulation of the nematic director perpendicular to the average orientation direction. [2] This remarkable phase of matter is polar, ferroelectric and optically biaxial. [2c] The NS phase could find widespread use in emerging technologies, provided current limitations around materials chemistry can be overcome.

References:

[1] (a) I. Dozov, Europhys Lett, 2001, 56, 247-253; (b) M. Cestari, et al., Phys. Rev. E, 2011, 84, 031704; (c) R. J. Mandle, Soft Matter, 2016, 12, 7883-7901; (d) C. T. Archbold et al., Liq. Cryst., 2017, 44, 2079-2088.
[2] (a) R. J. Mandle, et al., Phys. Chem. Chem. Phys., 2017, 19, 11429-11435; (b) A. Mertelj, et al., Phys. Rev. X, 2018, 8, 041025 (c) N. Sebastián, et al., Phys. Rev. Lett., 2020, 124, 037801

Host: Professor Cliff Jones