Glassy states: Concentration glasses and temperature glasses compared

The behavior of glass-forming systems in the equilibrium state above the glass temperature is still a heavily investigated field. Surprisingly, the behavior of the glass itself is less widely investigated. Even less investigated is the behavior of glass-forming materials in which composition is changed. Here we look at the behavior of glasses after temperature-jumps and compare that behavior with that of glasses subjected to concentration-jumps. Moisture and carbon dioxide are used as the plasticizing environments. Surprisingly, the glass created by jumping (down) to a given final condition via a change in concentration is more stable than that formed by a change in temperature – this in spite of the external condition of temperature and chemical activity (RH or carbon dioxide pressure) being the same. Furthermore, the concentration glass under such conditions has a higher excess volume than the temperature glass and its response does not ‘merge’ with that of the temperature glass, hence, the concentration glass is not the same as a temperature hyperquenched glass.