Sample preparation for chemical analysis or most physical testing is generally repeatable and often straightforward. This can sometimes be the case for rheology samples as well, but there are some things to consider when submitting a sample for rheological testing to the Zeta Rheology Centre.

Blue gel

  • A sample which contains obviously gritty or sandy particles can be difficult to test using plate-plate geometry, and sometimes it can be impossible to test using the most sensitive instruments.

  • Samples which settle moderately quickly, for example settling within 20 minutes, can give results which are markedly affected by the settling. For a plate-plate geometry this can result in a thin layer of liquid (often water) at the top plate, so the resulting shear stress or viscosity is lower than it should be. For a concentric cylinder geometry, settling can result in a compressed layer near the bottom of the concentric cylinders.

  • Some samples, especially shear thickening or shear thinning samples, behave quite differently once disturbed and can take quite some time to reach the original undisturbed rheology.

  • When changing conditions of shear rate or temperature and then reversing those conditions, it is common for samples to exhibit hysteresis, i.e. to record a different result when reversing the conditions.