Forces in an inhomogeneously ordered nematic liquid crystal: Stable and metastable states

Forces on plates separated a few nanometers and immersed in an isotropic liquid crystal are examined within a continuum approximation. The surface induced partial ordering of a liquid crystal is described using Landau-de Gennes phenomenological theory. Phase diagrams are presented to show the effect of surface coupling parameters, distance between the plates, and temperature on the stability and metastability of nematic and isotropic phases. Special attention is paid to the appearance of metastable phases. For selected examples we study distance and temperature dependences of the force. Values of surface coupling parameters are chosen in agreement with the results of recent experiments. For large distances between the plates the force scales with the second power of the surface coupling parameters and becomes an exponentially decreasing function of distance characterized with the nematic correlation length.