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SYGK: Symposium Rheologische Eigenschaften von Polymersystemen

SYGK III: HV III

SYGK III.1: Invited Talk

Monday, March 1, 1999, 11:00–11:50, HS 19

Surface anchored polymer layers: a way to adjust adhesion and friction — •Liliane Leger — Collège de France, CNRS URA 792, Physique de la Matière Condensée, 75231 Paris Cedex 05, France

We shall present systematic experiments on the polydimethylsiloxane (PDMS)-silica system which allow first to control the formation of surface anchored layers, and second to trace back what are the molecular parameters of both the chains in the surface layer and in the bulk material which govern the ability of the surface chains to enhance adhesion or to modulate friction. The adhesion between an elastomer and a surface can be enhanced by surface anchored chains, an effect governed by the degree of interpenetration between the surface layer and the chains in the bulk elastomer. The kinetics of formation of the interdigitated contact is highly non trivial and depends strongly on the organisation of the chains in the surface layer. Surface anchored chains also have a drastic effect on the friction between a polymer melt or an elastomer and a solid. Surface chains entangled with the bulk chains lead to high friction. But they are deformable and can elongate under the friction forces, leading to a transition from high to low friction when increasing the shear, due to disentanglement. Both to the level of friction and the critical shear rate for the transition can then be adjusted by choosing the molecular parameters of the surface anchored layer.