Morphological instabilities of a nonequilibrium nematic-isotropic interface

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Abstract
We present a detailed account of our videomicroscopy experiments on morphological instabilities of the nonequilibrium nematic-isotropic interface of the liquid crystal 8CB. For the parameter region chosen in our experiments, the time evolution of the amplitude of the most unstable spatial mode of the interface, during the planar-cellular bifurcation, can be well described by a third-order Landau-amplitude equation. Instability growth rates and cubic coefficients are in agreement with the two-sided model of solidification. Interface kinetics was also considered. In addition, we have made an analytical calculation of the Eckhaus boundary for solidification models. Even though we use an amplitude equation in our calculation, we have obtained a tilted Eckhaus boundary. This feature was previously believed to show up only in numerical calculations of complete models of solidification. We attempt to explain the final wave vectors measured in our experiments based on an Eckhaus instability. Another selection mechanism is mentioned. © 1996 The American Physical Society.