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 x 10(3) < M-w < 1.2 x 10(6) g mol(-1) were used within a temperature range that encompassed the bulk glass transition temperature, around which both M-w dependence and heterogeneous dynamics were measured. The range in M-w 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.