Mesoscopic-scale dielectric relaxation at the glass transition

Using scanning-probe-microscopy techniques, we have measured dielectric relaxation on ultrasmall, mesoscopic, length scales in a glassy polymer (polyvinyl acetate) film near its glass transition. The effective length scale sampled by these techniques is {~}50 nm. This is large enough to probe subsurface properties, but small enough to observe deviations from bulklike behavior in the form of fluctuations in the shape of the relaxation function near the glass transition. These fluctuations are argued to arise from cooperative dynamics and intrinsic heterogeneities on somewhat smaller length scales.