Published online by Cambridge University Press: 17 March 2011
We probed the glass transition temperature Tg at the surface of polystyrene (PS) samples with different molecular weights by embedding of gold nanoclusters. The embedding of the nano-clusters was monitored by x-ray photoelectron spectroscopy (XPS). The onset embedding temperature determined by XPS was taken as a measure for the Tg at the surface. We observed a small decrease of Tg at the surface relative to the bulk for all molecular weights (ΔTg= 2.5- 8.5 K). This decrease is small for short chains (MW = 3.6 kg/mol) and grows to a saturation for MW ≥ 44 kg/mol (ΔTg ≍ 8 K). This is in accord with the smaller relative increase in the number of degrees of freedom between bulk and surface for shorter chains.