Flexoelectro-optic properties of defect-free solvent-induced uniform lying helix

A uniform lying helix (ULH) alignment of cholesteric liquid crystals (CLCs) is of particular interest for flexoelectro-optic switching, which is a fast in-plane rotation of the optic axis when an electric field is applied perpendicular to the helix axis [1]. As the response times can be sub-millisecond, this opens up the possibility of realizing frame sequential color in next generation flat panel displays. However, achieving a high quality ULH still remains a challenge [2-4]. Here we propose a new method using solvent evaporation to spontaneously induce a defect-free ULH in a CLC, even in the absence of an electric field. Compared to the shear flow induced ULH (Fig.1a-c), the solvent induced ULH (Fig.1d-f) exhibits a contrast ratio between the bright and dark states that is a factor of 4 greater, due to the low number of defects in the structure (Fig.1f). The measured e1-e3 for E7 is found to be the same for both techniques (12.2±1.0 pC/m), direct observation of flexoelectrically-driven instabilities in the presence of an electric field.References: [1] J. S. Patel and R. B. Meyer, Phys. Rev. Lett. 58, 1538 (1987).[2] Y. Inoue and H. Moritake, Appl. Phys. Expr. 8, 071701 (2015).[3] P.S. Salter et al. Liq. Cryst. 36, 1355 (2009). [4] H.J. Coles et al. J. Appl. Phys. 99, 034104 (2006).