SEMINÁRIO DO INCT/NAP/GFCx
“Elastic continuum theory of the twist-bend nematic phases”
Palestrante: G. Barbero, Department of Applied Science and Technology, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino, Italy.
Dia: 20 de maio, sexta-feira, Auditório Adma Jafet, IFUSP, às 15h.
Abstract:
The recently discovered twist-bend nematic phase, NTB, has been theoretically predicted by Meyer [1] and Dozov [2], and has been experimentally evidenced by a number of studies (see e.g., Refs. [3], [4], and [5]). It may be viewed as a heliconical molecular arrangement in which the director n precesses uniformly about an extra director field, t, and corresponds to a nematic ground state exhibiting nanoscale periodic modulation [6]. To demonstrate the stability of this phase from the elastic point of view, a natural extension of the Frank elastic energy density is proposed [7]. The elastic energy density is built in terms of the elements of symmetry of the new phase in which intervene the components of these director fields together with the usual Cartesian tensors. It is shown that the ground state corresponds to a deformed state for which K22 > K33. In the framework of the model, the phase transition between the usual and the twist-bend nematic phase is of second order with a finite wave vector. The model does not require a negative K33 in agreement with recent experimental data that yield K33 > 0. A threshold is predicted for the molecular twist power below which no transition to a twist-bend nematic may occur. References [1] R. B. Meyer, in Molecular Fluids, edited by R. Balian and G. Weill, Vol. XXV-1973 of Les Houches Summer School in Theoretical Physics (Gordon and Breach, New York, 1976), pp. 273-373. [2] I. Dozov, Europhysics Letters 56, 247 (2001). [3] M. Cestari et al., Physical Review E 84, 031704 (2011). [4] D. Chen et al., Proceedings of the National Academy of Sciences USA 110, 15931 (2013). [5] V. Borshch et al., Nature Communication 4, 2635 (2013). [6] E. Virga, Physical Review E 89, 052502 (2014). [7] G. Barbero et al., Physical Review E 92, 030501 (R) (2015).
