Length scale of mechanical heterogeneity in a glassy polymer determined by atomic force microscopy

Using dynamic force microscopy, nanoscale mechanical heterogeneity in glassy polymer was characterized. The correlation length of heterogeneous viscoelasticity was measured to be ∼2.1 nm, consistent with the length scale of cooperatively rearranging regions at glass transition and is independent of molecular weight. Apparent energy dissipation with the variation of ∼57, originating from non-uniform distribution of local viscoelasticity, was revealed. The results provide definite experimental evidences on the nanoscale heterogeneity in glassy polymers and bear important insights in understanding the puzzling glass transition.