Study of the surface glass transition behaviour of amorphous polymer film by scanning-force microscopy and surface spectroscopy

The surface molecular motion of amorphous polymeric solids has been directly measured by lateral force microscopic (LFM), scanning viscoelasticity microscopic (SVM) and differential X-ray photoelectron spectroscopic (D-XPS) measurements. SVM and LFM measurements revealed that the molecular motion on the surface of the monodisperse PS film with Mn less than ca. 30 k was fairly active compared with that in the bulk, mainly due to the surface segregation of chain end groups. The chain end group segregation at the air/PS interface was verified by dynamic secondary ion mass spectroscopic depth profiling of the proton and deuterium ion for end-labelled PS film. These results suggest that surface T_g is depressed because of an increase in free volume near the surface region, induced by the preferential surface localization of chain end groups. D-XPS was utilized for the characterization of surface molecular motion of symmetric poly(styrene-block-methyl methacrylate) diblock copolymer [P(St-b-MMA)] films. It was confirmed by D-XPS that the surface molecular motion of the PS component in [P(St-b-MMA)] diblock copolymer films was gradually activated with decreasing depth from the air/polymer interface.