NONLINEAR DYNAMICS OF MELTED POLYMER LAYERS

A theory for non-linear rheology of molten polymer layers between soli d surfaces in the Rouse regime is discussed. It is shown that the effe ct of finite extensibility of polymer chains leads to I;he characteris tic 1/3 power law for the shear stress vs. shear velocity in the regim e of high velocities. It is also shown that bridging polymer fragments connecting the two surfaces play an important role for the rheology i f the effective monomer friction in the immediate vicinity of the surf aces is much higher than far from the surfaces. In particular we predi ct that shear stress is decreasing with shear velocity u in a limited range between u(1) and u(min). This effect results in a possibility of stick-slip periodical dynamics of the layer under a constant imposed velocity.