These characteristics are determined by a rheometer. These are available from companies like TA, Anton Paar, Thermo Fischer Sci, Malvern etc.; The measurements are performed as a function of the applied frequency . Important is to determine these values in the so-called visco-elastic regime. Here the values are not affected by the applied deformation or strain, but the signal is still strong enough to deliver a good signal to noise ratio. I hope this helps and please let me know, when you would need additional information’s.

Than you for your answer. Indeed I performed a Stress sweep test using a Thermo Fischer Sci , however I dont know how to calculate the Rheological parameters under oscillatory testing (stress sweep values, G' , elastic moduli; G'' , viscous moduli; h*, complex viscosity; tan (d) and y deformation. Can you help me out?

Normally the software is calculating these values directly and these calculation are based on the phase differences of the applied waves from stress to strain. Please find the link to wikipedia for additional information. https://en.wikipedia.org/wiki/Dynamic_modulus, I hope this helps and answer your question.

Hi Dorian,

In the Oscillation amplitude sweep test, the sample is loaded onto the rheometer (between plates, or a cone and plate or in a cup and bob) and subjected to rotational oscillations of increasing amplitude. These oscillations are initially very small and harmless, but grow in amplitude as the test progresses to determine the effect on the material’s structure. The Elastic and Viscous Moduli (G’ and G”) are measured continually and the test is usually stopped when the material just starts to break down, shown by a drop in one or both moduli. An oscillation amplitude sweep can be conducted with either increasing strains or increasing stresses being

controlled by the rheometer, and both give equivalent results.

One useful feature of this test is that it shows the modulus of a material while it is “at rest”, as initially the sample structure is not broken down at all. This linear viscoelastic region(LVR) is where initially the movement is so small that all of the sample’s structure is maintained. The length

of the LVR is also a direct measurement of the sample’s stability (when the moduli are plotted vs shear stress amplitude).

If a material has a higher viscous modulus than elastic modulus, we can say that the material is behaving like a liquid whereas if a material is more elastic than viscous, we can say it is a gel or solid.

The constitutive equations most simply put are effectively:

•Complex Modulus, G* = |Stress| / |Strain|

•Storage (Elastic) Modulus, G’ = |Stress| x Cos (phase angle)/|Strain|

•Loss (Viscous) Modulus, G” = |Stress| x Sin (phase angle)/|Strain|

Please note that inertia and other effects also need to be deducted from the data if calculated manually.

Regards,

Phil

Hi! Dorian,

I completely agree with Philips. And I would like to add some more comments to his answer:

This LVR can further be used for Frequency sweep and temperature sweep. where, the sample should not change internal structure due to applied stress. In another word, rheometer can control applied stress/strain to maintain the internal structure of material.

Is there an alternative system to measure this viscosity/elasticity relationship without a rheometer (or oscillatory stress sweep)?