Slip transition of a polymer melt under shear stress

We present the first direct measurements of the local velocity of a sheared polymer melt within the first 100 nm from the solid-liquid interface. For high enough shear rates we observe a sharp transition between weak and strong slip (i.e., a nonzero boundary fluid velocity) in the case of weak polymer-surface interactions [polydimethylsiloxane (PDMS) on silanated silica surfaces]. For strong polymer surface interactions the slip is strongly reduced. These results are compared to a theoretical model recently proposed by Brochard and de Gennes.