Note that, the apparent activation energy ∆E is not always constant nor independent of the temperature. For bulk viscoelasticity, the activation energy of viscous flow ∆Eη is calculated as the function of temperature with Williams-Landel-Ferry (WLF) parameters. However, ∆Eη converges to a constant value at higher temperatures than the glass transition temperature Tg, and the temperature dependence of ∆Eη can be practically ignored for small temperature differences at T > Tg + 100 K. Since Tg of PDMS is -123.3 ℃ , ∆Eη can be regarded to be constant.