An
interface is a surface forming a common boundary among two different
phases of matter, such as an insoluble
solid and a
liquid, two immiscible liquids, a liquid and an insoluble
gas or a liquid and
vacuum. The importance of the interface depends on the type of system: the bigger the quotient area/volume, the more effect the surface phenomena will have. Therefore, interfaces are very important in systems with big area to volume ratios, such as
colloids.