Relaxation dynamics in ultrathin polymer films

We have used photon correlation spectroscopy and quartz crystal microbalance techniques to examine the relaxation dynamics of ultrathin $(h<\mathrm{}400\mathrm{}\AA )$ polystyrene films in both supported and freely standing geometries. These studies probe relaxation dynamics of polymer films in which the glass transition temperature ${(T}_g)$ is reduced below the bulk value. Both the shape of the relaxation function and the dependence of relaxation time on temperature above the glass transition are remarkably similar to that of the bulk polymer, though the range of relaxation times is shifted according to the shift in $T_g.$ The results indicate that the microscopic relaxation dynamics of thin films remain similar to that of the bulk polymer even, in the extreme case in which the $T_g$ value is shifted more than 70 K below the bulk value.