RHEOLOGY OF CONFINED POLYMER MELTS UNDER SHEAR-FLOW - WEAK ADSORPTION LIMIT

The dynamics of a confined polymer melt between weakly adsorbing surfaces is considered theoretically. The finite chain extensibility is taken into account explicitly, and the tangential stress and the first and the second normal-stress differences are calculated as functions of shear rate gamma. For small shear velocities (u < u**) the surface slip is large, and the apparent viscosity, eta(app), is proportional to the layer thickness h and is independent of the shear rate. For very high shear rates, the surface slip is small and the tangential stress increases with velocity to the power 1/3. Alternatively, the apparent viscosity eta decreases as a function of gamma with a characteristic -2/3 power law.