Molecular weight dependence of near surface dynamical mechanical properties of polymers

We have made a detailed characterization of the molecular weight dependence of isothermal gold nanoparticle embedding into the surface of atactic polystyrene films. Polymers in the range 3 × 103 < Mw < 1.2 × 106 g mol−1 were used within a temperature range that encompassed the bulk glass transition temperature, around which both Mw dependence and heterogeneous dynamics were measured. The range in Mw also allows for comparison to recent studies on molecular glass surfaces – essentially covering the entire range of possible polymer sizes. The results show that there is a different manifestation of enhanced surface mobility for large and small polymer molecules. The transition between the mechanisms provides some bound on the size of a surface region with enhanced surface dynamics on glassy polystyrene surfaces.