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 −(0.45±0.02)n.