Flash differential scanning calorimetry was used to study the glass transition temperature T g of polycarbonate ultrathin films. The investigation was made as a function of film thickness from 22 to 350 nm and over a range of cooling rates from 0.1 to 1000 K/s. Polycarbonate spin cast films were floated on a layer of grease on the calorimetric chip. The results show a greatly reduced glass temperature for the thinnest films relative to the macroscopic value. We also observed that the magnitude of the glass temperature reduction decreases as the cooling rate increases with the highest cool-ing rates showing little thickness dependence of the T g . Dynamic fragility and activation energy at T g were found to decrease with decreasing film thickness. The results are discussed in the context of literature reports for supported and freely standing polycarbonate films.

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The present paper reports the results of a systematic rheological study of the dynamic moduli of 1-butyl 3-methylimidazolium tetrafluoroborate ([Bmim][BF 4 ]), 1-butyl 3-methylimidazolium hexafluorophosphate ([Bmim][PF 6 ]), and 1-ethyl 3-methylimidazolium ethylsulfate ([Emim][EtSO 4 ]) in the vicinity of their respective glass transition temperatures. The results show an anomalous aging in that the dynamic and the low shear rate viscosities decrease with time at temperatures near to, but above, the glass transition temperature, and this is described. The samples that are aged into equilibrium obey the time-temperature superposition principle, and the shift factors and the viscosities follow classic super-Arrhenius behaviors with intermediate fragility values as the glass transition is approached. Similar experiments using a high-purity [Bmim] [BF 4 ] show that using a higher purity of the ionic liquid, while changing absolute values of the properties, does not eliminate the anomalous aging response. The data are also analyzed in a fashion similar to that used for polymer melts, and we find that these ionic liquids do not follow, for example, the Cox-Merz relationship between the steady shear viscosity and the dynamic viscosity.

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