Relaxation times of nanoscale deformations on the surface of a polymer thin film near and below the glass transition

We report on measurements of relaxation times of nanometer-sized deformations resulting from the impact of individual energetic ions on poly(methyl methacrylate) surfaces at temperatures close to and below the glass transition Tg. The temporal evolution of the dimensions of the deformations is well described by a stretched exponential function, but with relaxation times τ(T) many orders of magnitude smaller than bulk values at the same T. The local Tg was around 860.2em0ex^∘C, roughly 300.2em0ex^∘C below the conventional bulk Tg. At the vicinity of the local Tg, τ(T) follows the Vogel-Fulcher type of T dependence, but at lower T a transition towards a less steep behavior is seen.