Analysis of Surface Molecular Motion of Amorphous Polymeric Solids on the Basis of Scanning Force Microscopy and X-ray Photoelectron Spectroscopy
Surface molecular motions of amorphous polymeric solids have been directly measured on the basis of lateral force microscopic (LFM), scanning viscoelasticity microscopic (SVM) and differential X-ray photoelectron spectroscopic (D-XPS) studies. SVM and LFM measurements of monodisperse polystyrene (PS) films revealed that, in the case of the number-average molecular weight, Mn less than ca. 30k, the surface was in a glass-rubber transition state at room temperature even though the bulk glass transition temperature, Tg was far above room temperature. The active molecular motion at the polymeric solid surface can be interpreted mainly in terms of excess free volume near the surface region induced by the surface segregation of chain end groups, which was confirmed by dynamic secondary ion mass spectroscopy (DSIMS). D-XPS measurement revealed that the surface Tg for the poly(styrene-block-methyl methacrylate) diblock copolymer films increased gradually with an increase in depth from the air/polymer interface.