Nanofriction of polymers: the complex role of adhesion

The objective of this work is to compare adhesion properties and nanoscale friction behaviour of model elastomers. Two polydimethylsiloxane elastomers, varying in their cross-linking density, are studied before and after extraction of free chains. Adhesion is measured by using a Johnson, Kendall and Roberts (JKR) experiment and nanofriction is quantified by using atomic force microscopy in contact mode. JKR experiment results indicate a higher adsorption ability of elastomers containing free chains. However, the interface created has a lower resistance to separation. In contrast, elimination of free chains allows an increase of adherence, despite a lesser wetting of the substrate. Nanofriction results are also very sensitive to the presence of free chains, with a higher friction before extraction of free chains. The influence of the cross-linking density is also discussed and interfacial molecular mechanisms are proposed for explaining the evolution of both nanoscale friction and adhesion properties.