Lower critical solution temperature

The lower critical solution temperature (LCST) or lower consolute temperature is the <a href="/facts/Critical_temperature/pkM7RLJK">critical temperature</a> below which the components of a mixture are <a href="/facts/Miscible/HwQaolbQ">miscible</a> in all proportions. The word lower indicates that the LCST is a <a href="/facts/Lower_bound/YJje9oC2">lower bound</a> 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 <a href="/facts/Upper_critical_solution_temperature/KAspLK4g">upper critical solution temperature</a> (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.
In the <a href="/facts/Phase_diagram/rcemFgW0">phase diagram</a> of the mixture components, the LCST is the shared minimum of the concave up <a href="/facts/Spinodal/vIlJQL8C">spinodal</a> and <a href="/facts/Binodal/NLxKuxV4">binodal</a> (or coexistence) curves. It is in general <a href="/facts/Pressure/eyc37GRG">pressure</a> 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 <a href="/facts/Triethylamine/6DjzaGGv">triethylamine</a>-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. The <a href="/facts/Nicotine/VQ6HcIrY">nicotine</a>-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.

Lower critical solution temperature open-in-new

Lower critical solution temperature