Comment on “Anomalous structural recovery in the near glass transition range in a polymer glass: Data revisited in light of temperature variability in vacuum oven‐based experiments”

Abstract

Recent efforts, fostered by a pioneering work by us, have shown the of multiple steps in the recovery of equilibrium of glasses. Jin and McKenna raise concerns regarding the validity of such scenario alleging that the multiple recovery steps would be an artifact arising from poor temperature control in the oven used for isothermal glass equilibration. We critically discuss Jin and McKenna arguments from both the viewpoints of scrutinizing previous literature data and that of the temperature control in the oven. In doing so, we provide compelling arguments that Jin and McKenna conjectures are unjustified and point out the need for efforts to describe glass dynamics significantly below the glass transition temperature, T g , by accounting for the presence of different relaxation mechanisms active in glass equilibration.

Comment on Comment on “Anomalous structural recovery in the near glass transition range in a polymer glass: Data revisited in light of temperature variability in vacuum oven‐based experiments”*

“…Cangialosi et al [ 3 ] made an interesting argument to invalidate the significance of the data by Czerniska‐Kubicka et al [ 7 ] that we had shown. They comment that if the data between 10 5 and 10 7 s aging time are truncated, “the existence of the double step recovery would also remain unseen.” Although we agree that the data by Czerniska‐Kubicka et al [ 7 ] would be more convincing if they had some data points between 10 5 and 10 6 s aging time, the Cangialosi et al [ 3 ] argument is not true.…”

“…Cangialosi et al [ 3 ] made an interesting argument to invalidate the significance of the data by Czerniska‐Kubicka et al [ 7 ] that we had shown. They comment that if the data between 10 5 and 10 7 s aging time are truncated, “the existence of the double step recovery would also remain unseen.” Although we agree that the data by Czerniska‐Kubicka et al [ 7 ] would be more convincing if they had some data points between 10 5 and 10 6 s aging time, the Cangialosi et al [ 3 ] argument is not true. In Figure 3, we compare the TNM model prediction of a single set of parameters for isothermal aging at 358 K to the “truncated” data of Cangialosi et al, [ 3 ] and it is clear that the enthalpy recovery data at longer aging times () do not follow the prediction for 358 K, but rather they appear to be results for lower aging temperatures, as was shown in our original manuscript to be due to issues related to the typical poor temperature control in a vacuum oven.…”

“…We think it is necessary to reassure that the purpose of the original manuscript [ 1 ] was to discuss the possible artifacts that could well lead to the unusual observation of two strong relaxations during enthalpy recovery experiments conducted and not to deny the possibility of secondary relaxations in general. Below is our response to the comment by Cangialosi et al [ 3 ]…”

“…Cangialosi et al [ 3 ] argue that the Kovacs [ 4 ] volume recovery data we showed do not extend to over 10 5 s aging time and further argue that the use of time–temperature superposition “would be acceptable only if the single decay scenario was true, but this cannot be proved by data extended up to only 10 5 s.” One issue of importance is that the Kovacs intrinsic isotherm data [ 4 ] we showed covered a somewhat greater range than 10 5 s (for the lowest temperature of 25°C in the criticized data the time was 191 h = 6.9 × 10 5 s). Thus, the data would be well into the plateau regime of the questioned enthalpy recovery data.…”

“…Cangialosi et al [ 3 ] also cite some work with significantly lower than and argue that these are related to secondary relaxations. Although these are interesting works, the specific study by Cangialosi et al [ 2 ] that we are commenting on for polystyrene only goes to 15 K below , which is far from the deep glassy state.…”