Clearing point

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As a clearing point ( engl. Clearing point ) refers to the transition from a liquid-crystalline mesophase in the isotropic phase.

If a liquid-crystalline phase is heated, the degree of order decreases. The degree of parallel orientation of the molecules is characterized by the degree of order. If the clearing point is reached, the order collapses immediately and the isotropic phase is formed. In it there is neither a long-range order nor a long-range directional order. This becomes visually visible in that the liquid, which previously appeared cloudy in the liquid-crystalline state due to its birefringence ( anisotropy ), suddenly becomes clear. Hence the origin of the word clarification point .

The IUPAC defines the clearing point as the temperature at which the transition between the mesophase with the highest temperature range and the isotropic phase occurs.

Individual evidence

  1. ^ TU Berlin, Demonstration Experiments with Liquid Crystals ( Memento from July 4, 2007 in the Internet Archive ), accessed on November 5, 2009.
  2. ^ Entry on clearing point . In: IUPAC Compendium of Chemical Terminology (the “Gold Book”) . doi : 10.1351 / goldbook.CT06857 Version: 2.3.1.

literature

  • GW Gray: Molecular Structure and the Properties of Liquid Crystals , Academic Press, New York 1962.
  • E. Bose, F. Conrat: About the viscosity anomalies at the clearing point of so-called crystalline liquids. In Phys. Time. , 9/1908, pp. 169-73.
  • T. Sluckin, Da Dunmur, H. Stegemeyer: Crystals that Flow: Classic papers from the history of liquid crystals , Taylor and Francis, 2004, ISBN 0-415-25789-1 .
  • S. Singh: Phase transitions in liquid crystals. In Physics Reports , 324/2000, pp. 107-269.
  • H. Kawamoto: The History of Liquid-Crystal Displays. In Proceedings of the IEEE , 90/2002, pp. 460-500.