SHEAR-DEPENDENT SLIPPAGE AT A POLYMER SOLID INTERFACE

We discuss shear flows of a polymer melt near a solid surface onto which a few chains (chemically identical to the melt) have been grafted. At low shear rates sigma < sigma* we expect a strong friction, analyzed in ref 1.1 Above a certain critical shear sigma* the grafted chains should undergo a coil stretch transition. In the stretched state, they are not entangled with the melt, and a significant slippage is expected when sigma > sigma*. This transition may be important in the processing of polymers, where a few chains from the melt can be bound on an extruder wall and play the role of the grafted chains.