A two-dimensional liquid (2D liquid) is a collection of objects constrained to move in a planar space or other

two-dimensional space A two-dimensional space is a mathematical space with two dimensions, meaning points have two degrees of freedom: their locations can be locally described with two coordinates or they can move in two independent directions. Common two-dimensiona ...

in a

liquid Liquid is a state of matter with a definite volume but no fixed shape. Liquids adapt to the shape of their container and are nearly incompressible, maintaining their volume even under pressure. The density of a liquid is usually close to th ...

state.

Relations with 3D liquids

The movement of the particles in a 2D liquid is similar to 3D, but with limited degrees of freedom. E.g. rotational motion can be limited to

rotation Rotation or rotational/rotary motion is the circular movement of an object around a central line, known as an ''axis of rotation''. A plane figure can rotate in either a clockwise or counterclockwise sense around a perpendicular axis intersect ...

about only one axis, in contrast to a 3D liquid, where rotation of

molecule A molecule is a group of two or more atoms that are held together by Force, attractive forces known as chemical bonds; depending on context, the term may or may not include ions that satisfy this criterion. In quantum physics, organic chemi ...

s about two or three axis would be possible. The same is true for the translational motion. The particles in 2D liquids can move in a 2D plane, whereas the particles is a 3D liquid can move in three directions inside the 3D volume. Vibrational motion is in most cases not constrained in comparison to 3D. The relations with other states of aggregation (see below) are also analogously in 2D and 3D.

Relation to other states of aggregation

2D liquids are related to 2D gases. If the density of a 2D liquid is decreased, a 2D gas is formed. This was observed by scanning tunnelling microscopy under

ultra-high vacuum Ultra-high vacuum (often spelled ultrahigh in American English, UHV) is the vacuum regime characterised by pressures lower than about . UHV conditions are created by pumping the gas out of a UHV chamber. At these low pressures the mean free path of ...

(UHV) conditions for molecular adsorbates. 2D liquids are related to 2D solids. If the density of a 2D liquid is increased, the rotational degree of freedom is frozen and a 2D solid is created.

''References''

Liquids Non-equilibrium thermodynamics Statistical mechanics Planes (geometry) {{thermodynamics-stub