Nematic
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A nematic liquid crystal is one where the centers of mass of molecules have no long-range order, but these molecules tend to be parallel to a common axis.
Nematics have no positional order. They do not share the same row formation as smectic liquid crystals. As a result they do not slide across each other in layers the way smectic liquid crystals do.
The molecules in a nematic liquid crystal point in the same direction, which is labeled by a unit vector called the director, denoted by 
.The orientation of the director may change gradually throughout the liquid crystal.
Opposite orientations of the director are indistinguishable, even if the molecules are asymmetric. Hence, the nematic order parameter is a second-rank tensor
where nα are the components of a unit vector along the major symmetry axis of the molecules and 
indicates a statistical average.
The transition from the isotropic liquid state to the nematic phase is a (often weak) first-order phase transition. The word nematic comes from the Greek νημα = thread. It refers to thread-like topological defects observed in nematics. They are called 'disclinations'. Hedgehog is the other type of topological defects in nematics.
Nematics have fluidity similar to that of ordinary (isotropic) liquids but they can be easily aligned by an external magnetic or electric field. An aligned nematic has the optical properties of a uniaxial crystal and this makes them extremely useful in liquid crystal displays (LCD).
