unvermischbare

Unvermischbare describes a property of substances that do not form a single homogeneous phase when mixed, most often referring to immiscible liquids. When two immiscible liquids are combined, they separate into two distinct layers, creating a clear phase boundary.

The lack of miscibility arises from differences in intermolecular forces and polarity. Polar solvents, such as water, exhibit strong hydrogen bonding, while many organic liquids are nonpolar. If the interactions between molecules of different liquids are weaker than the interactions within each liquid, mixing is unfavored, and the system minimizes its energy by remaining in separate phases. The saying like dissolves like captures this idea.

In a system of immiscible liquids, a macroscopic interface forms between the layers. The liquid with the lower density usually sits on top, while the denser liquid forms the bottom layer. At the interface, interfacial tension exists. Emulsions can be produced by dispersing droplets of one liquid in the other, often with the aid of emulsifiers or mechanical agitation, though such mixtures remain only dispersed and not truly miscible.

Some liquid systems are partially immiscible or exhibit temperature-dependent miscibility. They may be immiscible at room temperature but become miscible at higher or lower temperatures, or exhibit upper or lower critical solution temperatures.

Common examples include oil and water, and many hydrocarbons with water. Immiscible liquids are important in chemical engineering, solvent extraction, environmental science, and various industrial separation processes. In German-language scientific literature, unvermischbare is used to describe such immiscible systems.