A surface free energy resulting from electrical forces is present on all interfaces between solids and fluids, and between immiscible fluids. The electrical forces cause the surface of a liquid to occupy the smallest possible area and act like a membrane. The magnitude of the tension between two fluids is given by the interfacial tension. Interfacial tension (IFT) refers to the tension at a liquid/liquid interface. Surface tension refers to the tension at a gas/liquid interface, but is often used interchangeably with Interfacial tension. Interfacial tension is the tendency of a liquid to possess a minimum free surface when it is in contact with another immiscible liquid. Interfacial tension occurs because a molecule near an interface has different molecular interactions than an equivalent molecule within the bulk fluid.