Probing the surface Tg of monodisperse PS by local thermal analysis

The surfaces of compression-molded PS samples with different M-w (9.85 kg/mol-502 kg/ mol) and narrow molecular weight distributions were examined using an AFM equipped with a thermal probe in the local thermal analysis (LTA) mode to get further insight into possible explanations of a decrease in glass transition temperature (T-g) at polymer surfaces. No difference in T-g at the very surfaces could be detected for these samples. Instead, different molecular weights contribute to differences in the micro-thermomechanical behavior. A careful analysis hints to possibilities to use this analytic method for the determination of M-w and/or molecular weight distribution on polymeric surfaces. Furthermore, hints to a disentanglement of macromolecules with molecular weights lower than the critical molecular weight to form a random coil, initiated by the indentation with the thermal probe during the LTA experiment, are found.