Reduced variables and characteristic relaxation times
Time—temperature superpositioning is a common method to extend the range of viscoelastic data. Master curves can be calculated that cover many decades of time or frequency, and in principle enable properties to be predicted for times that are not experimentally accessible. Examples are given for dynamic and transient moduli, failure properties, and friction coefficients. However, the time—temperature superposition principle breaks down in the softening zone, which can lead to large errors in extrapolation of measured data. The cause of this breakdown is discussed. A recent development concerning the dynamics in condensed matter is the discovery of density scaling, whereby relaxation times and viscosities measured at different state points superpose as a function of temperature and density. The origin of this scaling behavior and its application are considered. Finally, the characteristic relaxation times of liquids and polymers are enumerated, along with their unanticipated invariance to thermodynamic conditions when the structural relaxation time is constant.
Keywords: time–temperature superposition principle, density scaling, William–Landel–Ferry (WLF) equation, thermorheological complexity, Arrhenius behavior, dynamic crossover, VFTH equation, potential energy, virial pressure
Oxford Scholarship Online requires a subscription or purchase to access the full text of books within the service. Public users can however freely search the site and view the abstracts and keywords for each book and chapter.
If you think you should have access to this title, please contact your librarian.