SLIPPAGE OF AN ENTANGLED POLYMER MELT ON A GRAFTED SURFACE

We analyse the way grafted polymers modify the slippage of an entangle d polymer melt on an ideal surface. We take into account the deformati on of the grafted chains in the flow (non-linear effects) and show tha t it alters significantly their efficiency as anti-slippers. We calcul ate the relation between the applied shear stress and the slippage vel ocity. At low velocities the friction of the undeformed grafted chains is strong. Above a certain threshold part of the chain relaxes throug h monomeric friction, and the stress becomes almost velocity independe nt. For even higher velocities the contribution of the grafted chains become small and a significant slippage is recovered. More generally, non-linear effects due to deformation of chains in flow are shown to b e of importance at most experimental and practical velocities.