The flexoelectro-optic effect in the uniform lying helix (ULH) geometry could provide many advantages over existing liquid-crystal technologies, however reliably forming the ULH has been problematic. Here, we achieve spontaneous, stable, and repeatable ULH alignment for materials with both positive and negative dielectric anisotropy in devices ranging from 1 to 7 μm in thickness without the need for any field application or flow-induced alignment, using a combination of weak homeotropic alignment conditions and unidirectional grooved surface profiles. The technique requires slow cooling from the isotropic phase and through the blue phase. Devices made using the technique display sub-millisecond and linear electro-optical responses.

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The chiral-flexoelectrooptic effect in a Uniform Lying Helix (ULH) configuration provides a sub-millisecond in-plane rotation of the optic axis with the application of a transverse field. This enables displays with a wide viewing angle without costly in-plane-type electrodes. The salient challenge is one of alignment of the ULH, which is not topologically compatible with uniform alignment surface treatments. Here, we create a micro-grooved surface structure with features on the micron scale by using a replica-moulding technique. When the cell is assembled, the micro-grooves create channels, and using surface-energy considerations, we explain how and show experimentally that the channels align a cholesteric material in the ULH geometry with the helicoidal axis oriented parallel to the channels. The resultant alignment provides a high level of contrast between crossed polarizers and exhibits an electrooptic response with a switching time of the order of tens of microseconds.

The contribution of flexoelectric polarization to the dielectric susceptibility in helicoidal liquid crystals is formulated for the static equilibrium case, and further in the case of a time-varying field. A dispersion of the dielectric permittivity due to the frequency response of flexoelectric switching is described. The special case of a negative dielectric-anisotropy nematic material is considered and experimentally shown to agree with the analytical theory. It is further demonstrated how relaxation of the flexoelectric contribution to the dielectric tensor in this special case can be exploited to switch between states in cholesteric liquid crystal structures by altering the applied time-dependent field amplitude, if Δε<0 and (e(1)-e(3))(2)/(K(1)+K(3))>-Δεε(0). Consequentially, a versatile mechanism for driving between states in liquid crystal systems has been demonstrated and its implications for technology are suggested, and include dual-mode, bistable, and transflective displays.

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