Measuring Viscosity of Materials with Dynamic Modulus

[gkiverm]

I understand that the dynamic modulus of a material is measured by inducing a sinusoidal force and measuring the strain response. Usually one gets a value for the storage and loss modulus. However, I don't understand how one would "quantify" how viscous a material is. I know a viscous material (less elastic) has a higher loss modulus and a lower storage modulus. But is there a certain ratio of the two variables where one considers a material mostly elastic or mostly viscous? I guess it would be easier if I can get a value for the dynamic modulus for some common materials. In addition, I understand the dynamic modulus is dependent on the frequency. So which frequency is common one to use when judging how viscous / elastic a material is?

 

[Chestermiller]

The ratio of the loss modulus to the storage modulus is the tangent of the phase angle. This is a measure of the ratio of viscous response to elastic response. The behavior varies with frequency. At very high frequencies, elastic behavior dominates, and at very low frequencies, viscous behavior dominates. So, in practice, it all depends on how rapidly the polymer is deforming in your actual process.

Chet

 

[gkiverm]

So if the tangent of the phase angle varies as frequency varies, is there a standard frequency people use to measure the tangent of the phase angle to compare the viscoelasticity of different polymers?

 

[Chestermiller]

So if the tangent of the phase angle varies as frequency varies, is there a standard frequency people use to measure the tangent of the phase angle to compare the viscoelasticity of different polymers?

No.

Chet

 

[PJC01]

I can provide some clarification on the measurement of viscosity using dynamic modulus. Viscosity is a measure of a material's resistance to flow, and it is closely related to the material's ability to store and dissipate energy. In the context of dynamic modulus, the storage modulus represents the material's ability to store energy, while the loss modulus represents the material's ability to dissipate energy. Therefore, a higher loss modulus and lower storage modulus indicate a more viscous material.

To quantify the level of viscosity, a common approach is to calculate the loss tangent, which is the ratio of the loss modulus to the storage modulus. A higher loss tangent indicates a more viscous material, while a lower loss tangent indicates a more elastic material. However, it is important to note that the loss tangent is also dependent on the frequency of the applied force, so it is essential to specify the frequency when reporting the loss tangent.

In terms of common materials, the dynamic modulus can vary greatly depending on the type of material and its composition. For example, liquids typically have a lower dynamic modulus compared to solids, and within solids, different materials can have vastly different dynamic moduli. Therefore, it is not possible to provide a single value for the dynamic modulus of common materials.

Regarding the frequency used to judge the level of viscosity or elasticity, there is no standard frequency that is universally used. It depends on the specific application and the properties of the material being measured. However, it is common to use a range of frequencies to obtain a more comprehensive understanding of the material's behavior.

In summary, the dynamic modulus can provide valuable information about a material's viscosity, but it is important to consider the frequency and other factors when interpreting the results. Additionally, the loss tangent can be used to quantify the level of viscosity, but it is also dependent on frequency. Therefore, it is crucial to specify the frequency when reporting the loss tangent.