Adhesion hysteresis studies of extracted poly(dimethylsiloxane) using contact mechanics

We present results of adhesion studies of poly(dimethylsiloxane) (PDMS) crosslinked hemispheres, before and after extraction, carried out using contact mechanics (the JKR apparatus.) Three types of PDMS networks were prepared with increasing crosslinker to-PDMS ratio (r = 1.7, 2.2, 2.7). Adhesion hysteresis was observed only after the PDMS hemispheres were extracted (toluene, Soxhlet, 20-24 h.) The size of hysteresis increased systematically with the decreasing ratio (increasing percentage of extracted weight.) Brief extraction yielded smaller hysteresis, which disappeared after 12 days. It is concluded that the entanglement of tethered chains and their interdigitation with cross-linked PDMS network at the interface may be the dominating mechanisms for the observed adhesion hysteresis.