Signatures of Structural Recovery in Polystyrene by Nanocalorimetry

Abstract

The intrinsic isotherm, asymmetry of approach, and memory effect experiments are performed for a high fictive temperature polystyrene glass in enthalpy space using nanocalorimetry. Using aging at times as short as 0.01 s and relatively high aging temperatures allows the complete evolution of all three of the signatures of structural recovery to be obtained for the first time in enthalpy space. The results from down jump experiments are compared to those obtained at lower temperatures using conventional differential scanning calorimetry (DSC) with respect to the time required to reach equilibrium, the apparent activation energy, and the Tool−Narayanaswamy−Moynihan (TNM) model parameters, and these results are independent of the measurement method being used; on the other hand, the physical aging rate is higher for the high fictive temperature glass.

Thickness dependence of structural relaxation in spin‐cast polynorbornene films with high glass transition temperatures (>613 K)

“…For the 60 nm film, the thickness of the film sharply rises in the last 300 min of aging. This nonmonotonic change in thickness on isothermal aging is somewhat reminiscent of the data obtained from asymmetry of approach to equilibrium . This increasing thickness on isothermal aging is likely associated with the nonequilibrium structure obtained from spin coating.…”

“…Additionally, residual solvent can lead to unusual structural relaxation processes . There are three common experiments (the simple isotherm, asymmetry of approach to equilibrium, and the memory effect) that provide insight into the nonlinear and path‐dependent characteristics associated with physical aging of glasses . For isothermal aging of glasses, three regimes are generally encountered: a nearly time‐independent initial plateau region, an intermediate aging regime, and a terminal aging regime .…”

“…51 There are three common experiments (the simple isotherm, asymmetry of approach to equilibrium, and the memory effect) that provide insight into the nonlinear and path-dependent characteristics associated with physical aging of glasses. 52,53 For isothermal aging of glasses, three regimes are generally encountered: a nearly time-independent initial plateau region, an intermediate aging regime, and a terminal aging regime. 43 The intermediate aging regime is typically of most interest and the aging rates are reported from this regime.…”

Glass Transition Phenomenon for Conjugated Polymers

“…However, the sample preparation is time consuming since it requires the stacking of several hundred layers of ultrathin film in order to meet the mass requirement . With the new developments of the nanocalorimetry, including flash DSC and AC‐chip calorimetry (We note here that the modulated DSC and the AC‐chip calorimetry are considered as dynamic measurements of T g ), which has the mass requirement of nanogram, measuring the T g of sub‐100 nm a single layer of polymer ultrathin film with DSC becomes possible and has drawn increasing attention …”

“…[333][334][335][336][337][338] Recently, the effect of nanoconfinement, for example, ultrathin film on the physical aging has drawn significant interest. [32,160,162,165,170,171,330,332,[339][340][341][342][343][344][345][346][347] In comparison to the bulk, despite the lower aging rate, an acceleration in physical aging in terms of the timescale to reach equilibrium is observed at the same aging temperature, [32,340] which is related to the depression in T g . By shifting the aging temperature to the same distance from relevant T g , Koh and Simon [32] showed that the aging rates for bulk and ultrathin film PS are comparable.…”