Communication: Experimentally determined profile of local glass transition temperature across a glassy-rubbery polymer interface with a T(g) difference of 80 K.

Studying the local glass transition temperature T(g) across a boundary, we investigate the characteristic length scales of cooperative dynamics. High molecular weight polymers have a large separation in time scales between cooperative segmental motion (α-relaxation) and chain diffusion allowing us to measure the local T(g)(z) profile across a glassy-rubbery interface of polystyrene/poly(n-butyl methacrylate) using fluorescence. We find this profile in cooperative dynamics does not correlate with the 7-nm wide symmetric composition profile of the interface, but instead is very broad, spanning 350-400 nm from one bulk T(g) value to another, and highly asymmetric, extending further into the glassy side.