Lower critical solution temperature

Polymer science
Properties Architecture Tacticity Morphology Degradation Phase behavior Mark–Houwink theory UCST LCST Flory–Huggins solution theory Coil–globule transition
Synthesis Chain-growth polymerization Free-radical polymerization Controlled radical polymerization ATRP RAFT Nitroxide-mediated radical polymerization Step-growth polymerization Condensation polymerization Addition polymerization
Classification Functional type Polyolefin Polyethylene Polypropylene Polyisobutylene Polyurethane Polyester Polycarbonate Vinyl polymers PVC PVA PVAc Polystyrene Structure Homopolymer Copolymer Gels Hydrogels Self-healing hydrogels
Characterization GPC FTIR X-ray crystallography DSC NMR TGA DMA Rheology Rheometry Viscometry
Scientists Flory Heeger MacDiarmid Shirakawa Natta Edwards de Gennes Ziegler Staudinger Goodyear Baekeland Hayward Braconnot
Applications Industrial production Extrusion Blow molding Applied coatings Protective Coatings 3D printing Consumer products Tires Whitewalls Cookware and bakeware Bakelite Food Container Vinyl record Kevlar Plastic bottle Plastic bag
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The lower critical solution temperature (LCST) or lower consolute temperature is the critical temperature below which the components of a mixture are miscible in all proportions.^[1][2] The word lower indicates that the LCST is a lower bound to a temperature interval of partial miscibility, or miscibility for certain compositions only.

The phase behavior of polymer solutions is an important property involved in the development and design of most polymer-related processes. Partially miscible polymer solutions often exhibit two solubility boundaries, the upper critical solution temperature (UCST) and the LCST, both of which depend on the molar mass and the pressure. At temperatures below LCST, the system is completely miscible in all proportions, whereas above LCST partial liquid miscibility occurs.^[3][4]

In the phase diagram of the mixture components, the LCST is the shared minimum of the concave up spinodal and binodal (or coexistence) curves. It is in general pressure dependent, increasing as a function of increased pressure.

For small molecules, the existence of an LCST is much less common than the existence of an upper critical solution temperature (UCST), but some cases do exist. For example, the system triethylamine-water has an LCST of 19 °C, so that these two substances are miscible in all proportions below 19 °C but not at higher temperatures.^[1][2] The nicotine-water system has an LCST of 61 °C, and also a UCST of 210 °C at pressures high enough for liquid water to exist at that temperature. The components are therefore miscible in all proportions below 61 °C and above 210 °C (at high pressure), and partially miscible in the interval from 61 to 210 °C.^[1][2]