Hybrid aligned nematic films placed onto an isotropic fluid substrate exhibit an unusual periodic stripe domain structure that appears only when the thickness of the film is smaller than a few tenths of a micrometer. We investigated the effect of a magnetic field on the threshold between the periodic stripe domains and the aperiodic deformed structure of the director. As experimentally observed, a magnetic field applied along the stripe domains favors a nonperiodic state with the director undistorted in the horizontal plane. The experimental findings are confirmed by a theory that takes into account not only the usual type of the elastic distortions, but also the so-called saddle-splay elasticity. A comparison of the experimental and theoretical data allows one to estimate that the saddle-splay elastic constant ${\mathit{K}}_{24}$ is of the same order of magnitude as the bulk elastic constants; this result agrees with independent studies of confined liquid crystal systems.

• Received 6 September 1994

DOI:https://doi.org/10.1103/PhysRevE.51.792