Modulated differential scanning calorimetry was used to thermally analyze separate thin films of poly( methyl methacrylate) (PMMA) and polystyrene (PS) that were adsorbed on silica and subsequently dried. The effects of surface coverage, adsorption medium, aging, and polymer/substrate interactions on the glass transition temperature (Tg) were investigated. For all of the treated samples, the half-height and the breadth of the Tg transitions increased with decreasing coverages compared to bulk and was the result of restrictions in mobility.
PMMA-treated samples had an increase in the glass transitions\u27 onset and end temperatures whereas PS treated samples with the same coverages had a slight decrease in the onset temperature and an increase in the end temperature. In addition, the Tg span for the PS samples was not as broad as compared to PMMA-treated samples. The differences in the thermal behavior were due to the differences in the polymers\u27 interactions with the substrate.
When PMMA was adsorbed from a polar solvent system, the Tg and its breadth increased compared to samples adsorbed from a poor solvent system. It was proposed that this was due to the polymer\u27s extended configuration on the substrate. After aging the polymer at room temperature for approximately a year, the thermal behavior of the low-coverage PMMA sample became more like that of the sample from the mixed solvent system. Presumably, the polymer chains rearranged into more stable configurations and attached more of their segments to the substrate --Abstract, page iv
