|
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.〔(【引用サイトリンク】url=http://goldbook.iupac.org/UT07280.html )〕 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.〔P.W. Atkins and J. de Paula, "Atkins' Physical Chemistry" (8th edn, W.H. Freeman 2006) p.185〕 Examples at higher temperatures are the aniline-water system at 168 °C (at pressures high enough for liquid water to exist at that temperature),〔Laidler K.J. and Meiser J.H. "Physical Chemistry" (Benjamin/Cummings 1982) p.230〕 and the lead-zinc system at 798 °C (a temperature where both metals are liquid).〔Laidler and Meiser p.232〕 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.〔Atkins and de Paula p.186〕 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.〔Sanchez, IC and Stone, MT, "Statistical Thermodynamics of Polymer Solutions and Blends" in ''Polymer Blends Volume 1: Formulation''. Edited by D.R. Paul and C. B. Bucknall, 2000 John Wiley & Sons, Inc.〕 ==Polymer-solvent mixtures== (詳細はpolymer solutions also have a lower critical solution temperature (LCST) or lower bound to a temperature range of partial miscibility. As shown in the diagram, for polymer solutions the LCST is higher than the UCST, so that there is a temperature interval of complete miscibility, with partial miscibility at both higher and lower temperatures.〔Cowie, J.M.G. "Polymers: Chemistry and Physics of Modern Materials" (2nd edn, Blackie 1991) p.174-176〕 The UCST and LCST of polymer mixtures in general depend on polymer degree of polymerization and polydispersity.〔 The seminal statistical mechanical model for the UCST of polymers is the Flory–Huggins solution theory. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Upper critical solution temperature」の詳細全文を読む スポンサード リンク
|