Adhesion between Solid Surfaces in Polymer Melts:  Bridging of Single Chains

The adhesion of solid surfaces across polymer melts has been studied with an atomic force microscope (AFM). As polymers we used poly(dimethylsiloxane) (PDMS, M w = 18 000), poly(ethylmethylsiloxane) (PEMS, M w = 16 800), and a diblock copolymer (PDMS-b-PEMS, M w = 15 100). Upon retraction, adhesion peaks were observed which we interpret as bridging of single polymer chains. Bridging occurred seldom (in each 20th force curve) in PDMS and more often in PEMS (in each 8th force curve) and was most prominent in the diblock copolymer, where a typical force curve contained 5−10 adhesion peaks. The mean detachment force decreased with increasing retraction velocity, indicating that the bond to the surface or tip is not a direct contact with the solid surface.