RHEOLOGY OF CONFINED POLYMER MELTS UNDER SHEAR-FLOW - WEAK ADSORPTIONLIMIT

The dynamics of a confined polymer melt between weakly adsorbing surfa ces is considered theoretically. The finite chain extensibility is tak en into account explicitly, and the tangential stress and the first an d the second normal-stress differences are calculated as functions of shear rate gamma. For small shear velocities (u < u*) the surface sli p is large, and the apparent viscosity, eta(app), is proportional to t he layer thickness h and is independent of the shear rate. For very hi gh shear rates, the surface slip is small and the tangential stress in creases with velocity to the power 1/3. Alternatively, the apparent vi scosity eta decreases as a function of gamma with a characteristic -2/ 3 power law.