Immiscibilitet

Immiscibilitet, or immiscibility, is the property of two liquids that do not form a single homogeneous phase when combined. Instead, they separate into distinct layers with a visible interface. In a typical two-phase system, the denser liquid settles at the bottom while the lighter liquid forms the top layer. A well-known example is oil and water.

Immiscibility arises from differences in molecular interactions, such as polarity and hydrogen-bonding tendencies. Polar liquids tend to mix with each other, while nonpolar liquids tend to mix with each other, but polar and nonpolar liquids often exhibit poor mutual solubility. Some liquid pairs are completely immiscible over a wide temperature range, while others are only partially miscible at certain compositions or temperatures, forming limited solubility and two-phase equilibria.

Temperature and the presence of additives can influence miscibility. Increasing temperature can sometimes enhance or reduce solubility, depending on the system. The addition of a third component, a cosolvent or surfactant, can promote mixing or stabilize emulsions, allowing dispersed droplets of one liquid to exist within the other.

Interfacial tension, the energy cost of maintaining the boundary between the two liquids, is a key parameter in immiscible systems. Phase diagrams for immiscible pairs show two-phase regions bounded by binodal curves, with tie lines indicating compositions in equilibrium at a given temperature.

Practical applications exploit immiscibility for separations, such as solvent extraction and purification, where different compounds preferentially partition between the immiscible liquids. Emulsions and emulsifying agents are used to stabilize mixtures of immiscible liquids in food, cosmetics, and pharmaceuticals. In Danish and related languages, the term immiscibilitet conveys this same concept.