Liquid crystal

A state of matter that flows like a liquid while retaining orientational or positional order among its molecules. Its partial order produces direction-dependent optical and electrical properties.

Liquid-crystal phase: A phase in which matter flows while retaining partial molecular order. The defining state can take several distinct ordered forms.
Director (liquid crystals): A vector-like description of the local average molecular orientation in a liquid crystal. The director tracks the alignment that fields and surfaces manipulate.
Liquid-crystal display: A flat-panel display that controls light using electrically reoriented liquid crystals. It converts molecular reorientation into visible pixels.
Nematic phase: A liquid-crystal phase with long-range orientational order but no long-range positional order. It is the simplest common phase and the basis of many displays.
Friedrich Reinitzer: An Austrian botanist who observed two melting points in cholesteryl benzoate in 1888. His observations first revealed the unusual intermediate state.
Mesogen: A molecule or molecular unit capable of forming a liquid-crystalline phase. Its shape and interactions make partial order possible.
Freedericksz transition: A field-induced reorientation of a liquid crystal above a threshold strength. It shows how an applied field can overcome elastic resistance to alignment.
Twisted nematic field effect: A display mechanism that switches light transmission by electrically unwinding a twisted nematic layer. This design made practical low-power liquid-crystal screens possible.
Smectic phase: A liquid-crystal phase in which molecules have orientational order and form layered positional structure. Its layering adds positional order beyond that of a nematic.
Otto Lehmann: A German physicist who studied and named liquid-crystalline materials in the late nineteenth century. His microscopy and experiments established the phenomenon as a distinct phase.

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