Time Regimes in Polymer Interdiffusion Determined by Marker Movement

Abstract

We have investigated interdiffusion of two thin polystyrene films by X-ray reflectometry. For two films of different molecular weight a net matter flux across the interface is predicted. Putting gold particles at the position of the interface, one can follow the displacement of these markers with time. Using the high-resolution of X-ray reflectometry, we have been able to detect a delay in the onset of bulk flow, which depends on molecular weight. There is a strong indication for a correlation between this induction time and the reptation or disengagement time. We assume that in this time regime the displacement of segments does not lead to a difference in polymer flux across the interface and thus no movement of markers is observed. The rearrangement of distorted molecules at the interface between the two films is also a possible reason for a delayed onset of bulk flow. The marker velocity at times shorter than the disengagement time of the long molecules is not influenced by the long molecules. It is determined by the diffusion coefficient of the small molecules only.