Write and erase mechanism of surface controlled bistable nematic pixel

Recently a new nematic bistable pixel, using simple monostable planar anchorings, has been proposed [4-6]. This pixel can be switched between two textures, having the same boundary conditions but different optical properties: one texture (U) is undistorted, whereas the other one (T) is characterized by the presence of a half-turn twist. The U --> T switching was obtained by abruptly dropping the driving electric field. A slow decrease of the driving electric field favors the T --> U transition. The electric field fall rate discriminates the kind of coupling between the boundary surfaces; hydrodynamic or elastic. Here we show the same behavior of this system by using square electric field pulses. We present experimental results concerning the critical values (amplitude and duration) of the driving signals, for which the elastic and the hydrodynamic effects are balanced and we measure their optimized values. Our results are in reasonable agreement with the theoretical predictions obtained by a simplified model.