J. Phys. II France
Volume 6, Numéro 2, February 1996
Page(s) 235 - 253
DOI: 10.1051/jp2:1996180
J. Phys. II France 6 (1996) 235-253

Pattern Formation in a Twisted Nematic Liquid Crystal Cell under an External Magnetic Field

Luca Carlotti, Sandro Faetti and Maurizio Nobili

INFM and Dipartimento di Fisica dell'Università di Pisa, Piazza Torricelli 2, 56126 Pisa, Italy

(Received 22 May 1995, revised 18 September 1995, accepted 6 November 1995)

We analyze the spatially inhomogeneous dynamic behaviour of twisted NLC layer in a magnetic field. When a magnetic field H is applied in the layer plane at a suitable angle $\beta$ with respect to the easy axis on the first surface, the relaxation toward the equilibrium texture occurs through a slow decay of unstable textures. For same values of $\beta$ and H, the relaxation of the unstable texture is strongly inhomogeneous and spatial domains occur everywhere. In this special case, a very rich dynamical behavior is observed together with the appearance of domains corresponding to unstable, metastable, and stable textures coupled with line defects and walls. We have studied and modelled the form and the properties of the different domains and interfaces, the velocities of the defect lines and the inhomogeneous-homogeneous character of the unstable texture relaxation. The static and dynamic features of the observed domains are in satisfactory agreement with the theoretical predictions.

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