Isothermal Frequency Sweeps

Purpose

To perform isothermal frequency sweeps at different temperatures that can be used to construct a master curve. 
An isothermal frequency-dependent measurement of mechanical relaxation behavior can be considered as a mechanical relaxation spectrum if the frequency range investigated is sufficiently large. 

Sample

Cured KU600 epoxy resin powder

Conditions 

Measuring cell: DMA with the shear sample holder

Sample preparation: Two cylinders, 5 mm in diameter and 0.56 mm thick were made by compressing fine uncured KU600 powder. The cylinders were mounted in the shear sample holder, heated at 250 C at 2 K/min, and then cooled to room temperature. 

DMA measurement: The measurement was performed in the frequency range 1mHz to kHz under isothermal conditions at different temperatures between 80 and 190 C. Maximum force amplitude 5 N; maximum displacement amplitude 20 um; offset control zero

Atmosphere: Static Air

The curves show the shear storage modulus in the frequency window 0.0001 to 1000 Hz measured at temperatures between 80 and 190 C.

Conclusions

In a frequency sweep experiment, the sample is measured at constant temperature in an experimentally accessible frequency window. If such an experiment is performed at two temperatures, T1 and T2 (where T1 < T2), the behavior measured at T2 in the frequency window is the same as that which would be measured at T1 at lower frequencies. The relaxation range can therefore be shifted across the frequency window by varying the temperature.
In other words, in such measurements the curves at lower temperatures correspond to those at the reference temperature and higher frequencies, and the curves at higher temperatures below the reference temperature, the same relaxation behavior is measured as at lower frequencies. 
Is it thought that there is a general equivalence between the (time) and temperature behavior at amorphous polymers close to the glass transition temperature - a polymer that has rubbery characteristics under certain conditions can behave as a glass transition temperature - a polymer that has rubbery characteristics under certain conditions can behave as a glass if the temperature is reduced or the time scale of the observation is decreased. Since the frequency-dependence is directly related to a corresponding time-dependence, the relationship is usually referred to as the time-temperature superposition principle. 
The relationship between temperature and frequency is described by the Vogel-Fulcher equation or the WLF equation.

^{Isothermal Frequency Sweeps | Thermal Analysis Application No. HB 27 | Application published in METTLER TOLEDO TA Application Handbook Thermosets Volume 1}