Source : Webster's Revised Unabridged Dictionary (1913)

Interfacial \In`ter*fa"cial\, a. (Geom.)
   Included between two plane surfaces or faces; as, an
   interfacial angle.

Source : WordNet®

interfacial
     adj : relating to or situated at an interface; "an interfacial
           layer"; "interfacial tension is the surface tension at
           the interface between two liquids"