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Testing the local dynamics of polymer chains at interfaces through mechanical experiments
We shall present and discuss several series of experiments in which the aptitude of surface anchored polymer chains to transmit stress through the interface is directly characterized. More precisely, we investigate the friction of a PDMS elastomer sliding on a brush of the same polymer in the quasistatic or dynamical regime, as a function of sliding velocity, grafting density (S) and molecular weight of the tethered chains. Two grafting regimes will be studied. At high S, the chains are confined outside the elastomer and the rheology of the thin layer can be studied, whereas at low S, small part of the chains, close to the free end which can penetrate into the sliding network induce an enhancement of the friction. In this regime, we will show that “start – stop” experiments, in which the elastomer is first slide at high velocity in order to extract all connector chains from the elastomer, then stopped for a certain duration, then slide again, can be used to test the internal dynamics of surface anchored chains. Besides, we will show that it is possible to connect the energy needed to extract a chain from the network as measured by friction experiment to previous experiments on the adhesion force between PDMS lenses to grafted chains in the JKR test.
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