Liquid Crystals

Liquid crystals are a class of organic molecules that behave like an intermediate phase between solids and liquids. By virtue of inhabiting such a special region, they display special optical properties that can be harnessed to develop powerful new technologies. Chelix has expertise in exploiting the helical structures of the cholesteric liquid crystals described below.

The atoms or molecules that make up a regular solid are rigidly fixed on a periodic crystalline grid. If the molecules also happen to be non-spherical, like a football, a frisbee, a ruler, or a slinky, their individual orientations (the directions they point in) will be fixed as well. This fixed order extends throughout the solid's structure.

Raising the temperature of such a regular solid will eventually melt the crystal into an liquid phase where the orientations and spacings vary throughout the liquid, and the regular solid structure is destroyed. For some materials, however, the transition is more gradual: there is an intermediate liquid phase - the liquid crystal phase - where the spacings between the molecules vary, but the directions remain nearly fixed and uniform (see the picture above).

The molecules that make up the special materials that form a liquid crystal phase are typically built of elongated, semi-rigid chemical groups. In their liquid crystal phase, the elongated groups all point in a similar direction, but they are randomly spaced through the material, very much like a box of compasses poured haphazardly out across a table. The compasses have landed all over the table, but their needles all point north.

The number of liquid crystalline phases is quite large. The most common and simplest is the nematic phase. In the oriented nematic sample shown below, all the elongated molecules point in the same average direction called the "director" (which would be "north" for the compasses on the table).

           Nematic liquid crystal phase

The director can be easily influenced by external constraints such as electric or magnetic fields. The ability to control the orientation of the orientation of liquid crystal molecules forms the basis of the highly successful Liquid Crystal Display (LCD) technology and other switchable devices, devices that can "switch" between different behaviors or properties by changing the orientation of the liquid crystal molecules.