Measurements on the surface glass transition of PMMA from the decay of imprinted surface corrugation gratings: the influence of molecular weight

Abstract The near-surface mobility of poly-methylmethacrylate (PMMA) chains is probed by means of optical diffraction. Particularly, we monitor the surface tension-driven decay of shallow surface corrugation gratings. The probe depth of the technique is about 100 nm. We report on quasi-static experiments, in which the sample temperature was ramped slowly from room temperature to a temperature well above the glass temperature, Tg. An estimate of the near-surface Tg is derived from the temperature at which the decay sets in, Tdec. For high molecular weight PMMA this decay temperature is much less than the bulk Tg as determined by calorimetry on the same material. For low molecular weight PMMA, this effect is absent.