Surface properties of silicone release coatings

The Harkins relationship, that the spreading coefficient of an adhesive on a release coating is the difference between the work of adhesion of the materials and the work of cohesion of the adhesive, has been found to apply to a variety of silicone release coatings. The works of adhesion and cohesion were estimated from contact angle data using the Owens and Wendt approach. The prediction of the Harkins relationship is obeyed by almost all the combinations of pressure-sensitive adhesive and release coatings we have examined. Release occurs when the spreading coefficient is negative and does not when it is positive. The main exception to this general spreading coefficient rule is the failure of polytetrafluoroethylene to release polydimethylsiloxane-based pressure-sensitive adhesives. The cause is believed to be roughness of the polytetrafluoroethylene surface.