  The dewetting dynamics of ultrathin polymer films, e.g. in the model system
of polystyrene on a polydimethylsiloxane-covered substrate, exhibits
interesting behavior like a fast decay of the dewetting velocity and a maximum
in the width of the built-up rim in the course of time. These features have
been recently ascribed to the relaxation of residual stresses in the film that
stem from the nonequilibrium preparation of the samples. Recent experiments by
Coppee et al. on PS with low molecular weight, where such stresses could not be
evidenced, showed however similar behavior. By scaling arguments and numerical
solution of a thin film viscoelastic model we show that the maximum in the
width of the rim can be caused by a temporal evolution of the friction
coefficient (or equivalently of the slip length), for which we discuss two
possible mechanisms. In addition, the maximum in the width is affected by the
sample age. As a consequence, knowing the temporal behavior of friction (or
slip length) in principle allows to measure the aging dynamics of a
polymer-polymer interface by simple dewetting experiments.
