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SYGK: Symposium Rheologische Eigenschaften von Polymersystemen

SYGK I: HV I

SYGK I.1: Invited Talk

Monday, March 1, 1999, 08:50–09:40, HS 19

Viscous properties of polymer brushes — •Jacob Klein — Department of Materials and Interfaces, Weizmann Institute of Science, Rehovot 76100, Israel

The frictional forces between two rubbing surfaces are dramatically reduced when they are coated by polymer brushes solvated by a good solvent. Here we discuss the viscous drag experienced by each of the brush layers as it slides past the other layer under compression. Both the extent of interpenetration of the brushes and the "effective viscosity" of the sheared interfacial region are considered. The relaxation mechanism is similar to that of a star-branched polymer, as all interacting chains are tethered by one end to one or the other of the surfaces. Comparison with results on shear of polystyrene brushes suggests that the approach to the glassy concentration becomes important as the brushes are progressively compressed (and solvent is squeezed out). At the highest compressions the data indicates that interfacial sliding takes place not between the brushes, but by slip at the brush/wall interface. The behaviour of polymer brushes with low glass transition temperatures is briefly considered.