The liquid phase of adhesives is most readily described by the theory of solutions. Adhesives act on phase boundaries. Yet right there, the fact that an adhesive is a solution does not fully describe its special performance. Some of the outstanding properties of adhesives are designed by the use non- soluble components, like Nanofillers, fibre reinforcements, color pigments, additives for the improvement of electrical and heat conductivity, etc. We would like to compare near phase boundary properties inside adhesives and outside near the substrates. We expect a relation between rheology and thermodynamical parameters of adhesion. Solutions are characterized by their chemical potential. We expect the above relationship to manifest itself by a change of the chemical potential near a phase boundary.