Surface molecular motion in thin films of poly(styrene-block-methyl methacrylate) diblock copolymer

Thin films of poly(styrene-block-methyl methacrylate) diblock copolymer [P(St-b-MMA)] with thickness ca. 50 nm were prepared by a dip-coating method. The surface T-g for the P(St-b-MMA) thin film was evaluated on the basis of the temperature-dependent X-ray photoelectron spectroscopic (TDXPS) measurement. The temperature at which the surface composition started to change was defined as the glass transition temperature, T-g, at the surface region. It was revealed that the surface T-g for P(St-b-MMA) was much lower than that for its bulk sample. Also, the depth dependence of T-g for P(St-b-MMA) was investigated on the basis of the combination of TDXPS and the angular-dependent XPS (ADXPS) method. T-g for P(St-b-MMA) decreased with a decrease in distance from the outermost surface. The molecular weight dependence of the surface T-g for P(St-b-MMA) was more pronounced than that in the bulk sample. and that was expressed as a function of M(n)(-(0.45 +/- 0.02)).