ELECTROCONVECTIVE INSTABILITIES IN FREELY SUSPENDED AND BOUND NEMATICLAYERS

EHD effects are studied in high conductivity MBBA layers aligned homeo tropically with respect to all the interfaces. Both freely suspended a nd bound films are examined under ac fields acting transversely to the line of sight. The orientational distortion originates as two periodi c waves close to the electrodes: The pattern symmetry is determined by their relative phase. For freely suspended films, both inphase and 18 0 degrees out of phase waves occur; the domains are non-centrosymmetri c in the former case, and centrosymmetric in the latter. For bound fil ms, only the in phase waves occur; further, close to the frequency cut -off, two oppositely drifting wave trains appear along the electrodes.