Isothermal dynamic frequency sweep

Dynamic-shear measurements are of the complex viscosity rj ) as a function of the dynamic oscillation rate (o), at constant temperature. These tests are defined as isothermal dynamic frequency sweeps. Since the dynamic frequency sweeps are conducted at a given amplitude of motion, or strain, it is necessary to ensure that the sweeps are conducted in the region where the response is strain-independent, which is defined as the linear viscoelastic region. This region of strain independence is determined by an isothermal strain sweep, which measures the complex viscosity as a function of applied strain at a given frequency. This ensures that a strain at which the dynamic frequency sweep may be conducted in the linear viscoelastic region is selected. 

Clearly, these early rheological studies of thermoplastic-modified thermosets were based mainly on traditional phase separation theory, and were focused on phase structure-viscosity changes indeed, most of them omitted the special effect of the thermoplastic phase on viscoelasticity and gelation. Although isothermal steady shear sweeps are widely applied, a lack of dynamic frequency sweeps the measurements. 

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