Mixing of liquids A and B and subsequent phase separation
When mixed, oil and vinegar will phase-separate
A phase diagram for two isotopes of helium, showing at bottom a range of temperatures and ratios at which they will phase-separate.

Phase separation is the creation of two distinct phases from a single homogeneous mixture.[1] The most common type of phase separation is between two immiscible liquids such as oil and water. Colloids are formed by phase separation, though not all phase separation forms colloids - for example oil and water can form separated layers under gravity rather than remaining as microscopic droplets in suspension.

## Phase separation in cold gases

A mixture of two helium isotopes (helium-3 and helium-4) in a certain range of temperatures and concentrations separates into parts. The initial mix of the two isotopes spontaneously separates into ${\displaystyle {\ce {^{4}He))}$-rich and ${\displaystyle {\ce ((}^3He))}$-rich regions.[2] Phase separation also exists in ultracold gas systems.[3] It has been shown experimentally in a two-component ultracold Fermi gas case.[4][5] The phase separation can compete with other phenomena as vortex lattice formation or an exotic Fulde-Ferrell-Larkin-Ovchinnikov phase.[6]