Elastic properties of bimesogenic liquid crystals

Abstract

The second nematic phase found in some bimesogenic liquid crystals with an odd flexible spacer has aroused considerable interest due to many unusual properties exhibited by them. However, the reason for such molecules to exhibit transitions to the modulated phase is still unclear. Dozov [Europhys Lett. 2001;56:247] predicted that negative K ₃₃ can lead to a modulated phase where the director has either splay-bend or twist-bend distribution. Though various theoretical studies have suggested that this scenario may be valid, no experimental evidence has so far been given. In order to study the influence of the elastic constants, we measured the splay and bend elastic constants in the ordinary nematic phase of a dimer material, CBC11CB, for temperatures down to 0.6°C above the Nx–Nu transition. Our results show that the bend constant is reduced by a factor of 2 compared with that closer to the I-Nu transition but is positive and the trend does not seem that K ₃₃ will extrapolate to zero or fall below it for the temperature range investigated. Compared to K ₁₁, K ₃₃ is reduced by a factor of 3, close to the Nu–Nx transition temperature.

Keywords:

• Nx phase
• dimers
• bimesogens
• dielectric permittivity
• elastic constants

Acknowledgements

One of the authors (RB) thanks IRCSET for the award of a research studentship. Collaboration between Dublin and Hull was funded by the EU BIND project 2008–12. Laboratory facilities were set-up by an SFI investigator award to JKV in 2003 and TIDA in 2012. Professor Kocot stay in Dublin was funded by SFI Walton Professorship. We thank G.R. Luckhurst, J.W. Goodby and D.J. Photinos for fruitful discussions.