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.Interfaces can be flat or curved.