https://doi.org/10.1351/goldbook.12813
Principle stating that the value of a viscoelastic property measured at a given temperature, after a given length of time or at a given frequency, is equal to the value of the property at a different temperature after a length of time or at a frequency equal to the given length of time or given frequency multiplied by a shift factor, \(a_{T}\) , with the value of the shift factor being independent of length of the time or frequency.
Note: The Williams–Landel–Ferry (WLF) equation provides a semi-empirical relation between the shift factor \(a_{T}\) and the temperature, at temperatures near the glass-transition temperature, \(T_{\rm{g}}\).