DIRECTOR FIELD PATTERNS OF NEMATIC POLYMER-SOLUTIONS AT ASYNCHRONOUS ROTATION IN A MAGNETIC-FIELD

A variety of different patterns is observed when a magnetic field rota ting with an angular frequency omega is applied on a nematic cell with homeotropic boundary conditions: To study the role of backflow in the formation of these dissipative structures, we compared the behaviour of dilute solutions of a mesogenic side group polymethacrylate in a lo w molar mass nematic liquid crystal (5CB) with that of the pure solven t. The dissolved polymer molecules lead to a strong reduction of the e xistence range of the so-called VRL-TI (viscosity reduction lattice tr ansverse instability) and complex states. For mass fractions w > 2 % o f the polymer these states were found to be suppressed completely due to the efficient reduction of backflow. The growth rate of the viscosi ty reduction lattices, which can still be observed, is in addition dep endent on the polymer concentration. Numerical calculations were perfo rmed to explain the behaviour.