Magnetic field effects in freely suspended nematics MBBA

Summary form only given. Magnetic field effects are rarely studied on a freely suspended nematic sample. The MBBA sample is spread on rectangular cavity and the initial homeotropic alignment with respect to all the boundaries was achieved spontaneously, which leads boundary layers at the cavity edges. On application of magnetic field the boundary layers expands almost non linearly with respect to the field but the growth rate was linear. The boundary layers advancing from opposite edges may or may not result in wall formation depending upon the initial alignment at the edges. Wall formation occurs whenever the defect lines associated with boundary layers are located either below or above the sample mid-plane. When the defect lines are on opposite sides of the plane, the layers coalesce smoothly. The wall is characterized as Brochard Leger wall. The linear wall is very stable and the ends are attached with defect line. At high magnetic field the wall splits into two defect lines at the rate linear with magnetic field. Sudden application of high magnetic field results in elliptical wall and they are metastable. From the decay rate these elliptical wall we could determine the elastic constants and viscosity coefficients.