Deep glassy state dynamic data challenge glass models: Configurational entropy models

Some open challenges in polymer physics*

“…If this is so, it would suggest the possibility of an ideal glass at lower temperatures than . Such a possibility has been discussed by Chen and McKenna [ 44 ] and further study would be required to establish the full behavior in this regime. For the amber data, we also remark that the fictive temperature, that is, the lowest temperature at which we could test the VFT extrapolation, was 92.6 °C which is 27.4 °C above .…”

“…At the same time, the ideas of a thermodynamic “ideal” glass transition are also part of the picture and the ideas were first put into a model by Gibbs and DiMarzio [ 43 ] who found from a lattice model that there was a point above 0 K where the configurational entropy went to zero and they associated this with the onset of a thermodynamic second order transition. These ideas have continued to be important since the just‐mentioned theories also use ideas of an entropy which goes to zero at a finite temperature, though recent study by Chen and McKenna [ 44 ] has suggested that the models could predict nondiverging dynamics if the entropy function chosen to relate the thermodynamics to the dynamics was different and did not go to zero at the Kauzmann temperature. In fact, in a recent study Berthier and Ediger [ 45 ] have essentially argued that it may not be possible to “measure” the “relaxation times that are too long to measure”.…”

“…[ 43 ] Thus, the idea that dynamics depend on thermodynamics and, in particular, on the entropy or configurational entropy became an important area of investigation in glass physics. We [ 44 ] have evaluated several entropy‐based models by treating them both with and without recourse to the entropy assumptions used by the original authors. Our thought in this is that the entropy itself is being extrapolated to the Kauzmann [ 5 ] temperature, thus reasonable alternatives to specific models could give different results.…”

“…The reader is referred to the work by Chen and McKenna [ 44 ] for the details, but as shown in Figure 13, both the Generalized Entropy (GET) Model from Douglas and co‐workers [ 20,41,42 ] and the Random First Order Transition (RFOT) theory from Wolynes and co‐workers [ 38–40 ] can predict strong deviations from the WLF/VFT behavior and give results that are much closer to the upper bound data from the ultra‐stable amber and amorphous Teflon than was the case, for example, of the MYEGA model. For the GET model, however, the configurational entropy was found to be virtually constant in the temperature range of interest and Chen and McKenna [ 44 ] felt that this was “unphysical.” In the case of the RFOT model, the configurational entropy used by Rabochiy and Lubchenko [ 60 ] gave diverging behavior (same as VFT/WLF in plot). However, under other considerations such as using the Milchev [ 61 ] entropy model or the entropy estimated from the calorimetric measurements on the very stable glasses, [ 44 ] the RFOT model does deviate strongly from the VFT/WLF extrapolation.…”

“…For the GET model, however, the configurational entropy was found to be virtually constant in the temperature range of interest and Chen and McKenna [ 44 ] felt that this was “unphysical.” In the case of the RFOT model, the configurational entropy used by Rabochiy and Lubchenko [ 60 ] gave diverging behavior (same as VFT/WLF in plot). However, under other considerations such as using the Milchev [ 61 ] entropy model or the entropy estimated from the calorimetric measurements on the very stable glasses, [ 44 ] the RFOT model does deviate strongly from the VFT/WLF extrapolation. This is seen in Figure 13B.…”