Magnetic field effect on periodic stripe domains in nematic liquid crystals

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 K24 is of the same order of magnitude as the bulk elastic constants; this result agrees with independent studies of confined liquid crystal systems.