Ferroelectric switching of electrically commanded alignment layers for liquid crystal displays

Abstract

Optical second harmonic generation (SHG) was used to probe the structural and dynamic properties of electrically commanded alignment layers for liquid crystal displays. The layers were 200nm thick and were made of siloxane-based side chain ferroelectric liquid crystal polymer (FLCP). The effect of an external dc electric field in the range of 0–2V∕μm on the SHG signal was probed in an empty sandwich cell and in a cell filled with an isotropic liquid (hexadecane). In both cases the nonlinear induced polarization shows characteristics of the “V-shaped” switching, which is associated with a relatively minor reorientational perturbation of the film. This signifies a presence of domain structure, which is strongly pinned to the substrates. The values of switching times deduced from the SHG response are two orders of magnitude larger from the values obtained by optical birefringence measurements. This observation suggests that in the top surface layer of the FLCP, which is mainly responsible for the birefringence and also for the so-called electrically commanded surface effect, the reorientation of the polymer side chains takes place much faster than in the regions close to the substrate.

The switching properties of chiral nematic liquid crystals using electrically commanded surfaces

“…23,24 Recently, this command surface switching concept has been advanced so as to enable electrically controllable command surface switching by using ferroelectric liquid crystals (FLCs) instead of photo-reactive materials. [25][26][27][28] In this case an electric field was applied perpendicular to the plane of the cell which resulted in an in-plane rotation of nanoscopic FLC layers at the surfaces. The result was a passive switch of the homogenously aligned bulk achiral nematic LC.…”