Lech Longa (Jagiellonian University): Nematics

In recent years, the search for new nematic phases has been pushed to the forefront of hot topics in liquid crystal research. It commenced with the identification of the twist-bend nematic (NTB) [1,2], marking the first observation of mirror symmetry breaking in a liquid state of achiral molecules, without the support of any long-range translational order. Subsequently, the splay-bend nematic phase (NSB) was discovered [3], followed by the splay nematic [4], biaxial orthorhombic (D2h) and monoclinic (C2h) nematics in hybrid colloids + 5CB [5,6], and more recently, the ferroelectric nematic phase [7].

It seems that the stabilization of NTB, NSB and Ns is to a large extent driven by excluded

volume effects of bent-shaped or wedge-shaped molecules. Alternatively, it is influenced by the flexopolarization mechanism which is responsible for softening of one of the elastic constants, either bend [1] or splay [3]. We tested this hypothesis by extending the Landau-de Gennes free energy of nematics [8-10] and through computer simulations [11,12]. We also delved into the mesoscopic-level description of the orientational order in hybrid systems.

Acknowledgments: Supported in part by Grant No. DEC-2021/43/B/ST3/03135 of the National Science Centre in Poland.

[1] Cestari M., Frezza E., Ferrarini A. and Luckhurst G. R., “Crucial Role of Molecular Curvature for the Bend Elastic and Flexoelectric Properties of Liquid Crystals: Mesogenic Dimers as a Case Study” J. Mater. Chem. 21, 12303 (2011).

[2] For a recent review see Jákli A., Lavrentovich O. D., and Selinger J. V., “Physics of liquid crystals of bent-shaped molecules”, Rev. Mod. Phys., 90, 045004 (2018).

[3] C. Fernández-Rico, M. Chiappini, T. Yanagishima, H. de Sousa, D. G. A. L. Aarts, M. Dijkstra, R. P. A. Dullens, “ Shaping colloidal bananas to reveal biaxial, splay-bend nematic, and smectic phases”, Science 369, 950–955 (2020).
[4] Mertel A., Cmok L., Sebastián N., Mandle R.J., Parker R.R., Whitwood A.C., Goodby J.W., and Čopič M. ‚“Splay nematic phase”, Phys Rev X 8, 041025 (2018).
[5] H. Mundoor, S. Park, B. Senyuk, H. H. Wensink, I. I. Smalyukh, “Hybrid molecular-colloidal liquid crystals”, Science 360, 768–771 (2018).[6] H. Mundoor, J-S Wu, H. H. Wensink and I. I. Smalyukh, “Thermally reconfigurable monoclinic nematic colloidal fluids”, Nature 590, 268–274 (2021).

[7] Chen X., Korblova E., Dong D., Wei X., Shao R., Radzihovsky L., Glaser M. A., Maclennan J. E., Bedrov D., Walba D. M., Clark N. A., “First-principles experimental demonstration of ferroelectricity in a thermotropic nematic liquid crystal: Polar domains and striking electro-optics”, PNAS, 117, 14021-14031 (2020).

[8] Longa L. and Pajak G., “Modulated nematic structures induced by chirality and steric polarization”, Phys Rev E. Rapid 93, 040701 (2016).[9] Pajak G., Longa L. and Chrzanowska A.: “Nematic twist–bend phase in an external field ”, PNAS, 115, E10303–E10312 (2018).

[10] Longa L., Tomczyk W.: “Nematic Twist-Bend Phase of liquid crystalline CB7CB dimers from Landau- de Gennes perspective”, J. Phys. Chem. C 124, 22761 (2020).

[11] L. Longa, M. Cieśla, P. Karbowniczek and A. Chrzanowska “Conformational degrees of freedom and stability of splay-bend ordering in the limit of a very strong planar anchoring” Phys. Rev. E 107, 034707 (2023).

[12] P. Kubala, M. Cieśla, and L. Longa “Splay-induced order in systems of hard tapers” Physical Review E, 108, 054701 (2023).