Thermal Characterization of Adsorbed Polystyrene Using Modulated Differential Scanning Calorimetry

The glass transition behavior of dried polystyrene (PS) samples adsorbed on silica, originally cast from carbon tetrachloride, has been studied using modulated differential scanning calorimetry (MDSC). The adsorbed amounts of the polymers on silica were very small, ranging from about 2 to 0.4 mg polymer/m2 silica. The glass transitions for the surface-adsorbed polymers were higher and broader than those for the bulk polymer. As the amount of adsorbed polymer decreased, the middle (Tg) and maximum (T+) of the transition increased significantly, while the minimum temperature (T-) decreased only slightly. The increased width and shift of the thermal transitions were not as large as those previously observed for adsorbed poly(methyl methacrylate) on silica; however, they were similar in that the breadth increased with decreased adsorbed amounts. The influence of the surface became less pronounced, and the behavior became more bulklike, as the amount of adsorbed PS increased