The upper critical solution temperature (UCST) or upper consolute temperature is the critical temperature above which the components of a mixture are miscible in all proportions. The word upper indicates that the UCST is an upper bound to a temperature range of partial miscibility, or miscibility for certain compositions only. For example, hexane-nitrobenzene mixtures have a UCST of 19°C, so that these two substances are miscible in all proportions above 19°C but not at lower temperatures. Examples at higher temperatures are the aniline-water system at 168°C (at pressures high enough for liquid water to exist at that temperature), and the lead-zinc system at 798°C (a temperature where both metals are liquid).
A solid state example is the palladium-hydrogen system which has a solid solution phase (H2 in Pd) in equilibrium with a hydride phase (PdHn) below the UCST at 300°C. Above this temperature there is a single solid solution phase.
In the phase diagram of the mixture components, the UCST is the shared maximum of the concave down spinodal and binodal (or coexistence) curves. The UCST is in general dependent on pressure.
The phase separation at the UCST is in general driven by unfavorable energetics; in particular, interactions between components favor a partially demixed state.
Read more about Upper Critical Solution Temperature: Polymer-solvent Mixtures, See Also
Famous quotes containing the words upper, critical, solution and/or temperature:
“Like many of the Upper Class He liked the Sound of Broken Glass.”
—Hilaire Belloc (1870–1953)
“I know that I will always be expected to have extra insight into black texts—especially texts by black women. A working-class Jewish woman from Brooklyn could become an expert on Shakespeare or Baudelaire, my students seemed to believe, if she mastered the language, the texts, and the critical literature. But they would not grant that a middle-class white man could ever be a trusted authority on Toni Morrison.”
—Claire Oberon Garcia, African American scholar and educator. Chronicle of Higher Education, p. B2 (July 27, 1994)
“I can’t quite define my aversion to asking questions of strangers. From snatches of family battles which I have heard drifting up from railway stations and street corners, I gather that there are a great many men who share my dislike for it, as well as an equal number of women who ... believe it to be the solution to most of this world’s problems.”
—Robert Benchley (1889–1945)
“The bourgeois treasures nothing more highly than the self.... And so at the cost of intensity he achieves his own preservation and security. His harvest is a quiet mind which he prefers to being possessed by God, as he prefers comfort to pleasure, convenience to liberty, and a pleasant temperature to that deathly inner consuming fire.”
—Hermann Hesse (1877–1962)