Variation of the storage modulus and the loss factor of VEM with frequency and temperature are shown in Figs. 14.1a to 14.1d.

Figure 14.1: Variation in storage modulus and the loss factor with frequency

The figures depict the following facts:

1. The shear modulus is low at low frequency and increase sharply beyond a critical frequency ω_cr
2. The loss modulus also reaches its maxima at the same frequency
3. A reverse change is observed in the shear modulus with respect to temperature
4. Here also, the loss modulus increases sharply at a critical temperature

The critical frequency and temperature actually depict a phase change in the polymer. For frequency, the change occurs from rubbery to glassy phase and the reverse for temperature.