DYNAMICS OF FLOW-INDUCED SURFACE EXCHANGE

The influence of functional groups on the dynamics of exchange between a flowing bulk melt and the channel wall was studied for oligomeric p olyolefins (up to C-16) using attenuated total reflectance Fourier tra nsform infrared spectroscopy. Surface transport is dominated by adsorb ed layers whose structure is determined by functional groups and chain length. There are two distinct time scales for surface transport, bot h of order minutes and surprisingly long for molecules of this size. T he longer time scale, which is observed only with chain functionalitie s that are likely to interact directly with the surface, appears to be caused by removal of an adsorbed mono- or bilayer. The shorter time s cale, which was reported previously by Dietsche et al. (1995) for the hexadecane/hexadecene system, appears to be caused by depletion of a m ore loosely-structured layer, but one in which the packing is still su fficiently different from that of the bulk to retard the dynamics.