Glass Transition Dynamics and Surface Layer Mobility in Unentangled Polystyrene Films

Tangle-Free Polymer Dynamics The dynamics of polymer chains at interfaces will differ from the dynamics in the bulk. While hard interfaces generally cause chain motions to slow down, at free surfaces the dynamics should generally speed up. A consequence is that for thin polymer films, there should be a reduction in the glass transition temperature ( T g ), but a wide range of effects have been seen in different polymeric materials. Now, Yang et al. (p. 1676 ) show that for short, unentangled polystyrene polymers, there is a direct correlation between the viscosity and the glass transition temperature, and that the reduction in T g is due to a surface mobile layer that dominates the behavior as the films decrease in thickness.