In contrast to rotational assay such as yield stress and thixotropy that apply a force in one direction, amplitude sweep is a back-forth oscillatory assay (think clothes washer agitator or wiggling a cube of Jell-O) based on deformation with an increasing amplitude (energy input) to probe viscoelastic properties leading up to and beyond its rheological "breakpoint".  Amplitude sweep is an important assay to properly quantify the LVER (Linear Viscoelastic Region) that correlates with rheological stability over either a strain controlled (sample displacement/height) or stress controlled (applied force/area) range.  The LVER input for subsequent frequency based assays described in the "Assay" tab (page top) should be well within the LVER determined with an amplitude sweep.  

 

It is also important to keep in mind that LVER typically changes with temperature.  Therefore, the amplitude sweep temperature used to determine the LVER should be similar to the temperature used for subsequent frequency modulated assays.

 

Figure 1 shows amplitude as increasing % strain or stress to define the upper limit of the Linear Viscoelastic Region (LVER), typically defined as 5% G' (elastic modulus; solid nature) decrease beyond which the sample's rheological integrity is increasingly destroyed.  The value of the upper limit of the LVER tends to correlate with physical stability and is a critical input for other oscillatory frequency modulated assays performed at the same temperature to ensure the sample's rheological integrity remains intact during the assay - otherwise confounding results are highly likely to be obtained. 

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Figure 2 shows amplitude sweep curves of 5 hydrogel samples comparing their differing G' (elastic modulus; solid nature) response with increasing amplitude (% strain) along with the upper limit of their LVER.   Subtle product formulation and processing modifications can alter rheological and performance properties that may be identified with rheometer outputs, but not necessarily with a viscometer.