Qualitative discrepancy between different measures of dynamics in thin polymer films.

We have used ellipsometry to measure the initial stages of interface healing in bilayer polystyrene films. We also used ellipsometry to measure the glass transition temperature T(g) of the same or identically prepared samples. The results indicate that as the film thickness is decreased, the time constant for the interface healing process increases, while at the same time the measured glass transition temperature in the same samples decreases as the film thickness is decreased. This qualitative difference in the behavior indicates that it is not always possible to make inferences about one probe of polymer dynamics from measurements of another. We propose a reason for this discrepancy based on a previously discussed origin for reduction in the T(g) value of thin films.