Splay-bend and twist-bend modulated phases in chiral nematic liquid crystals Drukuj
Wpisany przez Jacek Szczytko   
wtorek, 28 stycznia 2014 22:01

prof. Natasa Vaupotič

Department of Physics, Faculty of Natural Sciences and Mathematics, University of Maribor, Koroska 160, 2000 Maribor, Slovenia 5; Jozef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia

Szkoła IN: Środa 5 luty 2014, 104, Radiochemia, Miecznikowa (wejście od CENT), godz. 10:00

Due to the specific shape of the constituent molecules bent-core nematics and nematics made of bent molecular dimers can exhibit modulated nematic phases. Both the twist-bend and splay-bend nematic phases are theoretically predicted in achiral materials, depending on which elastic constant (twist or splay) is lower [1]. Because the splay elastic constant is very large in bent-core materials, so far, only the twist-bend nematic phases were observed in achiral nematics made of bent dimers [2].

Chiral nematics made of chiral dimers show by far more complex phase behavior. As reported by Zep et al [3], 6 nematic-type phases were observed in chiral dimers in a temperature range between the isotropic and crystal phase. 4 of the observed phases have less than 1 K temperature range, which suggests that there are several strongly competing interactions in the system.

In the talk I will present a theoretical model of modulated structures in chiral nematics. We study the stability of the twist-bend and splay-bend modulated structure superposed over the chiral helical twist (see Fig. 1). The model predicts the existence of the twist-bend and splay-bend structure in the same material and a phase transition between them.


Fig. 1: The splay-bend (top) and twist-bend (bottom) modulated structure superposed over the chiral twist. The structure is locally biaxial and as such represented by a block. In the splay-bend structure the angle  varies with  while in the twist-bend structure it is constant (), however the long axis of the block rotates on the cone.  is the modulation wavelength.


[1] R. B. Meyer, Structural problems in liquid crystal physics. Les Houches Summer School in Theoretical Physics, 1973. Molecular Fluids, eds Balian R, Weil G, 273 (Gordon and Breach, New York, 1976); I. Dozov, Europhys. Lett. 56, 247 (2001); S. M. Shamid et al., Phys. Rev. E 87, 052503 (2013).

[2] C. Meyer et al, Phys. Rev. Lett. 111, 067801 (2013); V. Borshch et al, Nature Commun. 4:2635 DOI: 10.1038/ncomms3635 (2013); D. Chen et al., PNAS 110, 15931 (2013).

[3] A. Zep et al, J. Mat. Chem. C 1, 46 (2013).

[4] N. Vaupotič, M. Čepič, M. A. Osipov, E. Gorecka, submitted

Szkoła odbywa się dzięki wsparciu projektu POKL UDA – POKL.04.01.01-00-100/10 "Chemia, fizyka i biologia na potrzeby społeczeństwa XXI wieku: nowe makrokierunki studiów I, II i III stopnia" prowadzonemu na Wydziale Chemii UW.

Poprawiony: wtorek, 11 lutego 2014 13:11