We have investigated the swelling of a polystyrene brush in cyclohexane at varying temperatures with angle-dependent ellipsometry. The brush was grown in situ on the base of a high index prism by the "grafting from" technique. In the dry state it has a thickness of d ) 134 nm. At the θ temperature it swells to about 600 nm. In accordance with the predictions from mean field theory, the brush thickness continuously increases with solvent quality. As the thickness increases, the shape of the segment density profile becomes smoother with a broad dilute transition region between the brush and the solvent.

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We have investigated the sorption behavior of polystyrene brushes with thicknesses of 10-200 nm in toluene vapor. The sorption curve displays a kink, which is attributed to the solvent-induced glass transition. The derivative of the sorption curve with respect to solvent activity ("osmotic capacity") shows a glass step at a certain characteristic activity a g. This is the analogue of the glass step observed in the heat capacity at Tg with differential scanning calorimetry. Both ag and the height of the glass step decrease with decreasing film thickness. The glass step is most pronounced after annealing the films at elevated temperatures in a vacuum. Due to accumulation of solvent in the film, the step disappears after repeated swelling/drying cycles.

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