Origin of the broad endothermic peak observed at low temperatures for polystyrene and metals in Flash differential scanning calorimetry*

Abstract

The glass transition behavior of polystyrene as a function of different cooling rates with scanning to two different end temperatures, 30 C and À80 C, was investigated for four different substrate conditions using Flash differential scanning calorimetry, a fast scanning nanocalorimetry technique. In addition, structural recovery of polystyrene was performed at 20 C for aging times from 0.01 s to 8 h with scanning to À80 C for the same samples. A broad endotherm appears to grow at low temperatures (T << T g ) as cooling rate decreases and aging time increases, which is influenced by the substrate underlying the film, as well as by the end temperature condition in the scanning experiment. On

Structure change of atactic polystyrene upon aging

“…These simulations show that the polymerization peak is primarily caused by correlations between main‐chain carbon atoms, whereas main second peak is caused by correlations between phenyl rings 7,8 . The enthalpy relaxation of this glass has been reported previously 9–15 . Given the high level of steric frustration in a‐PS, the evolution of its structure during relaxation may differ from that of other glasses.…”

“…7,8 The enthalpy relaxation of this glass has been reported previously. [9][10][11][12][13][14][15] Given the high level of steric frustration in a-PS, the evolution of its structure during relaxation may differ from that of other glasses. To our knowledge, only one measurement of the change of the X-ray structure factor upon annealing has been published.…”

Physical Aging and Glass Transition Dynamics of Semicrystalline Poly(lactic acid) for 3D-Printing Applications Investigated by Fast Scanning Calorimetry

“…It is determined as temperature fulfilling eq ∫ T normalf T l i q u i d ( c p , normall normali normalq normalu normali normald − c p , normalg normall normala normals normals ) normald T = ∫ T g l a s s T l i q u i d ( c normalp − c p , normalg normall normala normals normals ) normald T ′ where T liquid is any temperature above the glass transition region where the heat capacity is equal to the equilibrium value ( c p, liquid ), and T glass is a temperature well below the glass transition region where the heat capacity equals a quasi-equilibrium value ( c p, glass ). Knowing the limiting fictive temperature for the reference-cooling rate of 10 4 K/s, the limiting fictive temperature for other cooling rates, ß, can be determined through a relationship given by , normalΔ h normalr normale = prefix− ∫ T f ( 10 4 K / s ) T normalf normalΔ c…”

“…It is determined as temperature fulfilling eq where T liquid is any temperature above the glass transition region where the heat capacity is equal to the equilibrium value ( c p, liquid ), and T glass is a temperature well below the glass transition region where the heat capacity equals a quasi-equilibrium value ( c p, glass ). Knowing the limiting fictive temperature for the reference-cooling rate of 10 4 K/s, the limiting fictive temperature for other cooling rates, ß, can be determined through a relationship given by , where T f (10 4 K / s ) is the limiting fictive temperature at the reference-cooling rate of 10 4 K/s, Δ c p ( T ) is the temperature dependence of the specific heat-capacity step at the glass transition region (which can be obtained through the data in Figure ), and χ MAF is the MAF . Similar to the enthalpy-recovery peak after annealing at a constant temperature, a recovered enthalpy (Δ h re ) appears after cooling with a rate different from 10 4 K/s.…”

Editorial: In honor of Gregory B. McKenna's contributions to the field of polymer science

“…The work of Song et al [ 3 ] indicates a relaxation process different from α and β relaxation responsible for deep‐glass aging, but some care may have to be taken due to concerns raised in ref. [4].…”