Both samples are subjected to a sinusoidally increasing stress. Whilst the sample's structure is maintained, the complex modulus G* remains constant. However when the gel's intermolecular forces are overcome by the oscillation stress, the sample breaks down and the modulus falls.
Figure 1. Shear Stress Versus Complex Modulus For Two Samples.
Sample A gave a much shorter linear viscoelastic region than sample B and will therefore break down much more easily with vibrations and small movements. The length of the linear viscoelastic region is also a good indication of the stability of the gel to resist synuresis, where a layer of liquid forms on the surface of the gel.
A relatively quick amplitude sweep experiment can indicate the strength of a gel and its modulus. This can therefore be used to optimize dosing of gelation agents and other components.
Samples: Wound healing gels, toothpaste gels, etc
Geometry: Cone and plate system 4º/40 mm with a solvent trap
Stress amplitude sweep: 0.1 – 100 Pa Up Logarithmic
This information has been sourced, reviewed and adapted from materials provided by Malvern Panalytical.
For more information on this source, please visit Malvern Panalytical.