Introduction to Liquid Crystals

LCs | Twisted Nematic | FLCs | SSFLCs

What are Surface-Stabilized Ferroelectric Liquid Crystals?

Although the molecular director in bulk ferroelectric liquid crystals (FLCs) adopts a helical structure, Noel Clark and Sven Lagerwall [photograph] found in 1980 that by confining the LC material between closely-spaced glass plates (spaced closer than the ferroelectric helix pitch), the natural helix could be suppressed. This principle is illustrated in the polarized micrograph above, where helix lines are largely absent in the thinner (upper right) part of the cell. Clark and Lagerwall found that the smectic layers were oriented approximately perpendicular to the glass. Furthermore, they discovered that such cells could be switched rapidly between two optically distinct, stable states simply by alternating the sign of an applied electric field.

It was later established by Clark's group that there are two commonly found layer geometries, called bookshelf and chevron, the latter being portrayed in the Figure above. The electro-optic properties of an SSFLC depend strongly on the layer geometry as well as on the nature of the orienting properties of the bounding glass plates. Some images of SSFLC textures may be seen on another page.

SSFLCs are being studied in many research laboratories throughout the world. They form the basis for the development of optical shutters, phase plates, and high-resolution color displays.