text: Cassies law, or the Cassie equation, describes the effective contact angle θ for a liquid on a chemically heterogeneous surface, i.e. the surface of a composite material consisting of different chemistries, that is non uniform throughout. Contact angles are important as they quantify a surfaces wettability, the nature of solid-fluid intermolecular interactions. Cassies law is reserved for when a liquid completely covers both smooth and rough' heterogeneous surfaces.
  More of a rule than a law, the formula found in literature for two materials is;
  where and  are the contact angles for components 1 with fractional surface area , and 2 with fractional surface area  in the composite material respectively. If there exist more than two materials then the equation is scaled to the general form of;
  ,  with .