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Recent advances on nematic order reconstruction
R. Barberi1, G.Lombardo1, R. Hamdi1, F. Cosenza1, F.Ciuchi1, A. Amoddeo2
1 CNR IPCF LiCryL - Liquid Crystal Lab., Physics Department, University of Calabria, Via P. Bucci, Cubo 32/C, 87036 Rende (CS), Italy
2 Mechanics and Materials Department, University "Mediterranea" of Reggio Calabria, Via Graziella 1, Feo di Vito, 89122 Reggio Calabria, Italy

Investigations on Pi-cell, a sandwich cell with the director rotating by 180, are demonstrating the possibility to obtain nematic transitions between two textures with different topologies, for instance between an untwisted state and a Pi-twisted one. Fast topological changes can be observed by means of suitable electric fields or by micro/nano-confinement in the nematic bulk or close to a boundary surface. A strong frustration, in fact, as in the case of a strong local distortion, can induce transient and/or local biaxial states inside a nematic calamitic phase and the resultant nematic dynamics demands a full Landau-de Gennes Q-tensor description.
In this work, we present Q-tensor numerical models capable to describe the nematic order dynamics in full details, comparing theoretical results with experiments. We will also discuss as nematic order reconstruction close to a boundary surface with strong or infinite anchoring conditions can provide transitions equivalent to anchoring breaking.

1. R. Barberi, F. Ciuchi, G. Lombardo, R. Bartolino, G. Durand, Phys. Rev. Lett. 93, 137801 (2004).
2. F. Ciuchi, H. Ayeb, G. Lombardo, R. Barberi, G.E. Durand, Appl. Phys. Lett. 91, 244104 (2007).
3. G. Lombardo, H. Ayeb, F. Ciuchi, M.P. De Santo, R. Barberi, R. Bartolino, E.G. Virga, G.E. Durand, Phys. Rev. E 77, 020702 (2008).
4. G. Carbone, G. Lombardo, R. Barberi, I. Musevic, U. Tkalec, Phys. Rev. Lett. 103, 167801 (2009).
5. H. Ayeb, G. Lombardo, F. Ciuchi, R. Hamdi, A. Gharbi, G. Durand, R. Barberi, "Surface order reconstruction in nematics", accepted for publication by APL (2010).

"Jožef Stefan" Institute

University of Ljubljana
Faculty of Mathematics
and Physics

Center of Excellence