Surface Energetics of Polymers and Rubbers, Characterization of

Abstract

AbstractAdhesion of polymeric materials to various substrates, from metals to glass to other polymers, is a subject that continues to grow in importance, with today's technologies. The biocompatibility of polymer‐based implantable devices and prostheses is largely determined by the tendency of the material surfaces to be ‘wetted’ or adhered to by proteins. Surface and interfacial energy relationships determine in large part whether the adhesive and adherend achieve the intimacy of molecular contact that is a requisite for good adhesion. An aspect of the behavior of polymer blends and of block copolymers is that, depending on the relative surface energy of the components, and on the phase morphology and chain mobility, lower energy components may segregate to the surface to the detriment of interfacial adhesion, or perhaps promoting heterophase nucleation. There are numerous both technological and scientific motivations for the characterization of polymer surface energy.The objective in surface energy measurement is to characterize the free energy of a solid or a liquid surface (or, in general, an interface). The surface free energy per unit area (or surface tension) of polymers is a fundamental property. It may be measured in the solid, liquid, or solution state, but perhaps most often the intention is to refer the measured value to the solid state. Hence, one approach involves measuring the surface tension of polymer melts and low molecular weight liquid polymers by conventional methods and using one of several equations to extrapolate to values for the polymer in the solid state.Methods for determining the surface energy of solid polymers usually involve measuring the contact angle of a sessile liquid drop, and this methodology will be discussed in some detail. A relatively new technique for direct polymer surface energy measurement based on Johnson, Kendall, Roberts (JKR) (contact mechanics) theory will be discussed.