The work of adhesion per unit area, \(w_{\rm{A}}^{\unicode[Times]{x3B1} \unicode[Times]{x3B2} \unicode[Times]{x3B4} }\), is the work done on the system when two condensed phases $\ce{\upalpha\!}$ and $\ce{\upbeta\!}$, forming an interface of unit area are separated reversibly to form unit areas of each of the $\ce{\upalpha\!\updelta\!\mbox{-}}$ and $\ce{\upbeta\!\updelta\!\mbox{-}}$ interfaces. \[w_{\rm{A}}^{\unicode[Times]{x3B1} \unicode[Times]{x3B2} \unicode[Times]{x3B4} }=\gamma ^{\unicode[Times]{x3B1} \unicode[Times]{x3B4} }+\gamma ^{\unicode[Times]{x3B2} \unicode[Times]{x3B4} }- \gamma ^{\unicode[Times]{x3B1} \unicode[Times]{x3B2} }\] where \(\gamma ^{\unicode[Times]{x3B1} \unicode[Times]{x3B2} }\), \(\gamma ^{\unicode[Times]{x3B1} \unicode[Times]{x3B4} }\) and \(\gamma ^{\unicode[Times]{x3B2} \unicode[Times]{x3B4} }\) are the surface tensions between two bulk phases $\ce{\upalpha\!}$, $\ce{\upbeta\!}$; $\ce{\upalpha\!}$, $\ce{\updelta\!}$ and $\ce{\upbeta\!}$, $\ce{\updelta\!}$ respectively. The work of adhesion as defined above, and traditionally used, may be called the work of separation.