ADHESION ENERGY BETWEEN POLYMER NETWORKS AND SOLID-SURFACES MODIFIED BY POLYMER ATTACHMENT

The adhesion energy, or strain energy release rate, G, between polydim ethylsiloxane (PDMS) elastomers and flat silica surfaces modified by i rreversible adsorption and end grafting of PDMS chains, has been chara cterised through peel tests and 'JKR' experiments. The 90 degrees peel tests have been conducted down to very low velocity (5 nm s(-1)). In the 'JKR' experiment, a small spherical cap of elastomer is pushed aga inst the surface, and the area of contact is monitored as a function o f the applied load, allowing the determination of both G and the elast ic modulus of the elastomer, E. Systematic measurements have been made , varying the molecular architecture of both the elastomer and the gra fted layer (chain length and surface chain density). Our central resul t is that G, measured at the lowest possible accessible rates, passes through a maximum when the surface density of grafted chains increases . This can be rationalised in the framework of recent models of polyme r-polymer junctions, provided that the ability of the grafted chains t o penetrate into the network is accounted for. When the velocity of th e advancing fracture is increased, the measured adhesion energy increa ses strongly and non-linearly, contrary to the predictions of molecula r models based on the suction mechanism.