The molecular dynamics in thin polymer layers having a free upper interface is investigated by means of Broadband Dielectric Spectroscopy and AC-calorimetry. Down to film thicknesses of ∼10 nm no shifts in the average relaxation time and no broadening of the dynamic glass transition are detected for polystyrene, poly(methyl methacrylate), poly(vinyl acetate), poly(γ-benzyl- l -glutamate) and poly(2-vinyl pyridine). This experimental finding restricts to a few nanometers the length-scale of a possible alteration of the polymer mobility in the vicinity of free interfaces.
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Serghei et al. (2008) studied this question.
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