As we have seen in the previous section, liquid crystal phase lies in between the solid and the liquid phase. Are there any other subphases in the liquid crystal region ?
It turns out that, depending on their amount of order (which can for example be imposed with external constraints) liquid crystals show several different subphases.

NEMATIC PHASE
This phase is characterized by the fact that the molecules try to align themseleves along the same director but there is not evidence of any positional order among them. The molecular orientation can be modulated applying external Electric fields to the material. The nematic phase is one of the most used in technological applications. LCD (Liquid Crystals Displays) are a great example of it. A special class of Nematic liquid-crystals goes under the name of Chiral Nematic. The name is due to the ability of the molecules to selectively reflect polarized light (see LCD section for more details).

SMECTIC PHASE
This phase is peculiar of liquid crystals at lower temperature. The main characteristic of it is that other then align themselves in a particular direction they also lie in layers. The motion of the molecules is contrained within these layers which can slide over one other like soup.
In this phase is present some kind of positional order. Depending on the orientation of the molecules over these planes we can classify different classes of smectic phases. For instance smectic of class A have the director perpendicular to the smectic plane.

Smectic phase (Class A)

In the class C the situation is similar to the one in the previous case but the director forms a constant angle respect to the normal to the smectic plane.

Smectic phase (Class C)

As in the nematic case the smectic of class C have a substate in which they show a chiral phase. The angle in this case will rotate from plane to plane forming an helicoidal path.