Chiral ferronematic liquid crystals: a physico-chemical analysis of phase transitions and induced helical twisting

ABSTRACT

A possibility was assessed to modify physico-chemical properties of ferronematic mixtures by introducing additional mesogenic and non-mesogenic components. The mixture, consisting of RM734 and DIO at the 70:30 weight ratio of the components, was doped with nematic 5CB and its chiral isomer CB15. This allowed a substantial lowering of the ferronematic temperature range, as well as induction of helical twisting in both nematic (N) and ferronematic (N_F) phases. The effects of 5CB and CB15 on the N_F to N phase transition were nearly identical, but the isotropic transition temperature decreased more strongly upon addition of CB15. Optical transmission vs. temperature measurements showed lower transmittance in the N_F phase, probably due to scattering on the domain boundaries. In the vicinity of the N_F → N transition, a noticeable range of anomalously low transmission was noted both on heating and cooling, suggesting a complex character of molecular reorientation features. In the chiral N_F (N*_F) system, helical twisting was recorded using Grandjean-Cano wedge, with the helical pitch decreasing upon cooling in both N* and N*_F phases. In the cooling mode, transient undulations emerged in the N*_F phase. The complex picture of the ferronematic transition is supported by POM images taken at different temperatures.

GRAPHICAL ABSTRACT

KEYWORDS:

• Chiral dopant
• ferroelectric nematic phase
• phase transition
• Grandjean-Cano texture
• undulation structures
• differential scanning calorimetry
• optical transmission
• polarising optical microscopy

Acknowledgments

The authors thank W. Becker (Merck, Darmstadt, Germany) for his generous gift of nematic liquid crystal E7, field service specialist V. M. Danylyuk (Dish LLC, USA) for his gift of some Laboratory equipments, graduate student of Physics Department K. Thapa and his advisor Prof. O. D. Lavrentovich (Advanced Materials and Liquid Crystal Institute, Kent State University, USA) for the helpfull discussions. The authors are incredibly grateful to the Commander in-Chief of the Armed Forces of Ukraine General V. F. Zaluzhnyi, Ukrainian soldiers, volunteers, NATO countries and other allies, who support Ukraine during the russian-Ukrainian war started on 24 February 2022.

Disclosure statement

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

Additional information

Funding

The research was supported by the National Academy of Sciences of Ukraine within projects [№ 0122U002636, № 0122U200141, B#197 and 3/2022-B].