Imiscibile

Imiscibile, often written immiscible in English, refers to liquids that do not mix to form a single homogeneous phase. When combined, immiscible liquids separate into two distinct liquid phases with an interface between them. The degree of miscibility is determined by the balance of intermolecular forces: liquids that differ greatly in polarity or hydrogen bonding tendencies tend to be immiscible. In many cases, unfavorable interactions between unlike molecules lead to positive enthalpy of mixing that cannot be compensated by entropy, resulting in limited or zero mutual solubility. The result is a high interfacial tension between the phases.

Some liquid pairs are completely immiscible under common conditions, such as water and many nonpolar organic liquids (for example, oil). Others are partially immiscible, showing a two-phase region over certain compositions that may change with temperature, pressure, or added solutes. These systems are described by phase diagrams and may exhibit upper or lower critical solution temperatures (UCST or LCST) in which the miscibility changes with temperature.

In practice, immiscible liquids are exploited in separation and extraction processes, solvent partitioning, and liquid-liquid extraction. Emulsions and surfactants can stabilize mixtures that would otherwise separate. In laboratory and industrial settings, understanding immiscibility guides solvent selection, purification, and design of separation equipment such as separatory funnels and extractors.

Common examples include water–oil systems, and several organic solvents that do not mix with water. Conversely, miscible pairs mix in all proportions and form a single phase. Immiscibility is a fundamental aspect of liquid-phase behavior, with broad implications in chemistry and engineering.