MODULATED DIFFERENTIAL SCANNING CALORIMETRY IN THE GLASS-TRANSITION REGION

Modulated differential scanning calorimetry (MDSC) presents two time s cales to the measurement of the glass transition, a fast one, fixed by the modulation time period, and a slow one, fixed by the average, und erlying heating or cooling rate. The same situation arises in dynamic mechanical and dielectric measurements. The various time effects on th e glass transition are discussed and documented with experiments on th e reference material polystyrene. It will be shown that MDSC can measu re the glass transition temperature largely independent of the thermal history (and the heating or cooling rates), but dependent on the modu lation frequency, This distinguishes MDSC from standard calorimetry th at can measure accurate data on the glass transition only on cooling, a mode of operation often neither convenient nor very precise.