smectic-A phase
Quick Summary
In nematic arrangements the crystals are randomly positioned with all their long axes pointing in essentially the same direction, given by a vector known as the director. In smectic arrangements the crystals are further constrained to parallel planes; in smectic A the director is perpendicular to these planes, while in smectic C the director is at some other angle to the planes.
The smectic-A phase is a type of liquid crystal where molecules are arranged in layers. Within each layer, the molecules are parallel to each other and perpendicular to the plane of the layer. This structure exhibits discrete translational symmetry in one direction (perpendicular to the layers) but continuous translational symmetry within the layers. Unlike solid crystals, the molecules in a smectic-A phase can flow, and their positions within the layers are disordered. This intermediate state between a liquid and a solid is crucial for technologies like liquid crystal displays (LCDs).123
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