Physical aging of selenium glass: Assessing the double mechanism of equilibration and the crystallization process

Abstract

This work focuses on the study of the physical aging of a selenium glass by differential scanning calorimetry (DSC) and fast scanning calorimetry (FSC). Aged samples of 30 and 40 years old at room temperature were analysed by classical DSC, and their enthalpies of recovery were calculated, showing that the glass has reached its thermodynamic equilibrium and is stable over time. The study of accelerated physical aging by using FSC on a rejuvenated sample allows reproducing the way by which this glass has reached its thermodynamic equilibrium at the laboratory time scale. We evidence that the glass reaches its equilibrium state in one or two steps, depending on the gap between the aging temperature and the glass transition temperature, resulting from the difference in the mechanisms governing the relaxation process. Furthermore, a second phenomenon is evidenced, consisting in the crystallization of the glass once the equilibrium has been reached for aging temperatures close to the glass transition temperature.

Polymers of Intrinsic Microporosity─Molecular Mobility and Physical Aging Revisited by Dielectric Spectroscopy and X-ray Scattering

“…Therefore, overcoming the two major obstacles of physical aging and penetrant-induced plasticization of PIM membranes has become a larger field of research in membrane science. In this context, it is worth to note that in general, physical aging seems to be due to localized processes which can also be multi-step and/or sequential processes even at temperatures far below T g . − In order to suppress physical aging, a widely adopted strategy is to stabilize the microporous structural arrangement in the polymer by adding rigid porous inorganic or organic fillers to the polymer matrix (see, for instance, refs – ). With regard to the latter point, it is known that the presence of a free interface will accelerate physical aging.…”

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”

“…These reports are on a wide variety of glass formers: low molecular weight organic compounds, [21] chalcogenide glasses, [22,23] metallic glasses, [24][25][26] glassy polymers [27,28] and very recently the most simple polymeric glass former, that is, selenium. [29] The latter study is especially relevant as the aging time dependence of the glass enthalpy was monitored for up to 40 years. This allows separating the twotime scales of equilibrium recovery at aging temperatures significantly below T g .…”

Physical aging of the 62.5GeS2-12.5Sb2S3-25CsCl chalcogenide glass: Assessing the mechanisms of equilibration and crystallization

“…The use of the fast-scanning calorimetry (FSC) has generated many recent studies 7,26,27 proving that the physical aging can accelerate the ability to crystallize by forming nuclei after reaching the equilibrium state. This phenomenon known from a theoretical point of view is difficult to evidence experimentally because it appears after the complete structural relaxation, but we highlighted it through the study of a selenium glass considered as an ideal glass former according to its simple structure 28 . This previous study highlighted that for aging temperature closed to Tg, the molecules constituting the glass have enough mobility to enhance the crystallization process after reaching the thermodynamic equilibrium.…”