Influence of grafting density on wall slip of a polymer melt on a polymer brush

We have investigated the shear flow of a polydimethylsiloxane (PDMS) melt on a PDMS brush of well-controlled density. As the shear rate, γ̇, is increased, we show the existence of a slip transition from a weak slip regime, where the extrapolation length of the velocity profile, b , is a constant b 0 , to a strong one, where γ̇ sticks to its value at the transition γ̇ ⋆ . We discuss the influence of the grafting density Σ on b 0 and γ̇ ⋆ . We compare our results with a recent microscopic model.