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Aging of Glasses


We have shown that the aging of glasses is governed by the same mechanisms that determine the dynamic properties of the corresponding liquids and that this aging can be described much simpler than by the 30 year old models used so far. When a liquid is cooled fast enough, it becomes a glass - a "frozen liquid" that is out of equilibrium and no longer represents the energetically most favorable state.


Thus all glasses age, i.e. their physical properties change with time when they try to regain their equilibrium state, which is of considerable technical importance in glass fabrication and for the degradation of glassy materials in applications as glass fibers, optical components, or polymers. We found that the time characterizing the rapidity of the aging is identical to the time characterizing the microscopic molecular motions and that this time changes itself with time during aging. We found a self-consistent recursive formula describing the time-dependence of physical properties of the glass, which is straightforward to apply and involves less parameters than the models used so far by glass physicists and engineers (see Figure). It reveals parameters that are fully consistent with those characterizing the dynamics response of the equilibrium liquid to external perturbations.

 

 aging

Time dependence of dielectric loss (a-c) or modulus (d) at various frequencies for four glassformers after quickly cooling from the liquid into the glassy state. The lines are fits with the new approach. The main fit parameters are the same for all frequencies and fully consistent with the results at temperatures above the glass transition. (from: P. Lunkenheimer, R. Wehn, U. Schneider, and A. Loidl, Glassy Aging Dynamics, Phys. Rev. Lett. 95, 055702 (2005).)


To learn more, see: P. Lunkenheimer, R. Wehn, U. Schneider, and A. Loidl, Glassy Aging Dynamics, Phys. Rev. Lett. 95, 055702 (2005).