Temporal Progression
The speed at which an out-of-equilibrium glass undergoes structural changes toward a more stable state determines its long term stability. This metric, known as the physical aging rate, quantifies the shift in relaxation times as a function of the aging time. The parameter describes the progress of structural relaxation.
Kinetic Coefficient
Calculating the evolution of properties requires tracking how specific parameters change on a logarithmic timescale. In amorphous polymers, the physical aging rate is often defined by the shift in the dielectric or mechanical relaxation spectra. These shifts scale with the logarithm of time.
Material Property
The slow densification of the amorphous matrix modifies both the mechanical and thermodynamic characteristics of the material. An elevated physical aging rate results in a more rapid transition from ductile to brittle behavior. This embrittlement affects the reliability of load-bearing polymer structures because the material loses its ability to deform plastically under stress.
Environmental Influence
The temperature difference between the glass transition point and the storage temperature influences the progression of structural relaxation. Sufficiently close to the transition, the physical aging rate reaches a maximum before falling to zero at equilibrium. This non-monotonic trend guides the thermal treatment of glassy materials.
