A frequency sweep is a particularly useful test as it enables the viscoelastic properties of a sample to be determined as a function of timescale. Several parameters can be obtained, such as the Storage (Elastic) Modulus (G'), the Viscous (Loss) Modulus (G"), and the Complex Viscosity (η*).
The storage modulus can be used as a measure of the elastic component of the sample and similarly, the loss modulus – the viscous component of the sample.
Whichever modulus is dominant at a particular frequency will indicate whether the fully structured material appears to be elastic or viscous, in a process of similar time scale. The mechanical response of most dispersion coatings is viscoelastic, since the presence of suspended solids, high additive concentrations, colloidal thickeners, etc. will induce some sort of structure upon the bulk phase. Some examples are considered in the following frequency sweep data sets.
Figure 1 is typical of a non-associated particulate dispersion and the viscosity is almost independent of frequency. The viscous modulus is dominant over the elastic modulus and both of these are highly dependent on frequency. In this situation, sedimentation is likely to occur.
Figure 2 shows a weakly- structured system. The viscous modulus will still dominate over the elastic modulus. However, the difference between these is less great than in the nonassociated system. The complex viscosity is also now dependent on the frequency. In this system sedimenation may occur.
Figure 3 shows what could be classified as a well-structured (gelled) system. In this case particles are strongly associated, the storage modulus (G') is greater than the loss modulus (G") and both are almost independent of frequency. Sedimentation is unlikely to occur.