J. Phys. II France
Volume 7, Numéro 5, May 1997
Page(s) 707 - 727
DOI: 10.1051/jp2:1997154
J. Phys. II France 7 (1997) 707-727

The Effect of Dissolved Side-Group Polymers on Pattern Dynamics in Nematic Liquid Crystals in a Rotating Magnetic Field

E.E. Pashkovsky1, W. Stille2, G. Strobl2 and D. Talebi2

1  Institute of Macromolecular Compounds, Academy of Sciences of Russia, Bolshoi pr. 31, St. Petersburg 199004, Russia
2  Fakultät für Physik, Universität Freiburg, Hermann-Herder-Str. 3, 79104 Freiburg, Germany

(Received 17 June 1996, revised 12 November 1996, accepted 13 February 1997)

Patterns formed by inversion walls in nematic layers exposed to a rotating magnetic field were studied. Dilute solutions of a mesogenic side group polymethacrylate in a low molecular weight liquid crystal (5CB) were used in comparison with the pure solvent. As found in a previous work, in this system the intensity of backflow (fluid flow induced by director rotation) can be controlled by the polymer concentration due to a specific increase of shear viscosity coefficients. In the synchronous regime of director rotation no significant effects of backflow on the dynamics of the walls are observed. Dynamic solitons known from the synchronous regime were also found at asynchronous rotation, when soliton lattices are formed by continuous nucleation. Here comparison with theory for given values of the lattice period shows soliton currents significantly reduced by backflow. Two of the three additional pattern forming states exclusively found at asynchronous rotation were completely suppressed in solutions with sufficient polymer concentration. The third of these states is affected by backflow in the growth rate of its patterns. Numerical calculations were performed to explain behavior of the patterns in the asynchronous state. For pure 5CB a quantitative comparison with the experiment was possible.

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