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A modulated nanoindentation technique has been developed for thermal transition analysis of polymer thin films. The procedure was applied to glass transition measurements of poly-t-butylacrylate, with results that compare well with shear-modulated force microscopy and differential scanning calorimetry. The advantages of the modulated indentation technique are twofold: (i) it provides in situ experimental access to material properties in nanoscopically confined geometries, and (ii) it incorporates well-defined indenter geometries, which provide a means for quantitative thermorheological analysis that is not available with conventional scanning probe microscopy. The experimental procedure and critical test parameters are detailed. [ABSTRACT FROM AUTHOR]

Interfacial glass transition temperature (T[sub g]) profiles in spin cast, ultrathin films of polystyrene and derivatives were investigated using shear-modulated scanning force microscopy. The transitions were measured as a function of film thickness (δ), molecular weight, and crosslinking density. The T[sub g](δ) profiles were nonmonotonic and exhibited two regimes: (a) a sublayer extending about 10 nm from the substrate, with T[sub g] values lowered up to ∼10 °C below the bulk value, and (b) an intermediate regime extending over 200 nm beyond the sublayer, with T[sub g] values exceeding the bulk value by up to 10 °C. Increasing the molecular weight was found to shift the T[sub g](δ) profiles further from the substrate interface, on the order of 10 nm/kDa. Crosslinking the precast films elevated the absolute T[sub g] values, but had no effect on the spatial length scale of the T[sub g](δ) profiles. These results are explained in the context of film preparation history and its influence on molecular mobility. Specifically, the observed rheological anisotropy is interpreted based on the combined effects of shear-induced structuring and thermally activated interdiffusion. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]