Measurement of interfacial adhesion between glassy polymers using the JKR method

The surface and interfacial energies of polymers are measured, using the JKR-type experiments. A novel method has been developed to prepare samples of glassy polymers for adhesion measurements. A thin layer of a polymer is coated on the surface of an O₂-plasma modified cross-linked poly(dimethylsiloxane) [PDMS] spherical cap resulting in the formation of a composite. Using the JKR theory, the surface energies of polystyrene [PS] and poly(methyl methacrylate) [PMMA] are determined from the measurements of the contact radius as a function of applied load. The results of the JKR-type experiments are compared to adhesion measurements done using the surface forces apparatus (SFA). Adhesion hysteresis was observed for PS-PS contact as well as PMMA-PMMA contact. However, no hysteresis was observed for PDMS-PDMS, PDMS-PS, and PDMS-PMMA contacts. The exact origin of the hysteresis is not clear at present. The current evidence suggests that hysteresis is due to rearrangement of the interface during contact.