A summary of rheology

There are two types of test in conventional rheometry as follows:

In a typical flow experiment, the response to shear and flow of a non-Newtonian fluid is assessed. The sample is subjected to a variable shear stress and rate, and the respective flow curve is obtained after the breaking down of any structure present.

Non-destructive rheological testing (NDT) is performed under low stress and strain without damaging the colloidal structures under test. In this way, the strength of particle interactions in a suspension, and the shape retention, i.e. elasticity of these structures can be determined.

Typical NTD involves dynamic oscillatory testing. This technique applies a small deformation to a sample, and the contribution of the solid-like and liquid-like character of viscoelastic materials (gels, hydrocolloids) is measured in terms of their storage (G'), loss (G") moduli and loss tangent (tan).

For weak gels, G'>G" in the linear viscoelastic region. The complex (dynamic) viscosity referring to both viscous and elastic characters can be calculated accordingly.

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