The vertical axis represents resistance to deformation (increasing stiffness or viscosity) while the horizontal axis represents a progression from solid (elastic) behaviour to liquid-like (viscous) behaviour. The rheological parameters complex modulus (G*) and phase angle (δ) respectively quantify these properties, and both can be gained from a simple oscillation test. Structured fluids and soft solids - the viscoelastic materials we see in real life – occupy various positions on this “map”, their location defined by their complex modulus and phase angle.

A typical application for this kind of characterisation is in the assessment of dispersions. A solid suspension undergoing flocculation will show a progression upwards and to the left as the modulus rises and the associating particles form a network that deforms elastically under applied stress. A suspension can then be tested at weekly or monthly intervals with a simple oscillation stress sweep.