Influence of the network structure of silicone rubber on time-dependent autohesion as mechanism for self-healing

The influence of structure of polymer networks and molecular weight of the constituting polymers, on their tackiness and time-dependent autohesion as mechanism for crack repair has been studied. The polymer used was polydimethylsiloxane (PDMS), crosslinked with a trifunctional silane. The tack experiments were performed with a tack testing device, developed specially for this purpose, and the data were measured in terms of maximum tack force. The networks were characterized with swelling and mechanical properties. High molecular weight PDMS shows autohesion increasing with time in a form of a logarithmic curve. The autohesion curves of low-molecular weight PDMS show a maximum over a certain contact time, then the tack decreases to a plateau. The data indicate that the generally accepted ¼ power law increase between tack and time does not apply in this case. The exponent obtained is noticeably lower. The slopes of time–dependence curves obtained at different pulling speeds, however, behave according to theory, but the values are always lower than predicted. This sort of behavior can be attributed to the high polydispersity of the polymers used.