Adhesion and friction behaviors of polydimethylsiloxane - a fresh perspective on JKR measurments

The self-adhesion of a variety of polydimethylsiloxanes (PDMS) has been investigated using a newly developed JKR apparatus that can also determine the associated friction behaviour of the same sample. The results have been interpreted using the complete JKR model by incorporating the indentation data also in the analysis. By varying the molecular mass Mc of PDMS from 6 to 28 kg/mol the elastic modulus E decreases from 1.16 to 0.71 MPa while the work of adhesion remains about constant. In contrast measurements of the friction of the same systems indicate an increase of the friction force. Introduction of dangling chains leads to a strong decrease of E from 1.16 to 0.56 MPa for low Mc and from 0.71 to 0.09 MPa for high Mc and again only to minor changes in W. The latter results can be understood from an inward distribution of the dangling ends.