The role of free chains in adhesion and friction of poly(dimethylsiloxane) (PDMS) networks

The aim of this study is to analyse the influence of some molecular parameters (crosslinking density, presence of free chains) on both adhesion and friction properties of elastomer networks. The polymers used are polydimethylsiloxane (PDMS) networks with different initial molecular weights. Networks were studied before and after extraction of free chains in toluene. The substrate is a smooth glass plate. The experimental procedure uses both friction (pin-on-disk tribometer) and adhesion (tack test) measurements, associated with surface analysis (static and dynamic wetting). Adherence energy increases with PDMS molecular weight. Friction measurements results, however, exhibit a higher friction stress for low molecular weight PDMS. The influence of chain length is discussed and some molecular mechanisms are proposed to explain both friction and adhesion behaviors. The major role of pendant chains is underlined.