What are the advantages ?
DWS holds significant advantages compared to mechanical rheology, and other microrheology techniques such as DLS or particle tracking:
- DWS is a passive measurement method: no force is applied to the sample, and the measurements are always in the linear regime for rheology. This contact-free approach with no moisture loss due to the sealed conditions is ideal for a variety of samples since they can be reused. In particular, it enables stability monitoring over a very long time.
- The frequency range accessible is larger than any other technique: up to 106 Hz for G’ and G’’. This is illustrated in the figure below.
- The measurements are fast: a single acquisition of less than 1 nm yields data on the full frequency range at once. This enables the monitoring of fast processes occurring in the sample. An acquisition over a similar frequency range using a mechanical rheometer would last an order of magnitude more.
- DWS is extremely sensitive and can detect particle displacements of a few nanometers. This allows for the characterization of subtle changes in the microstructure of a sample.
- remarkably small sample volumes may be used: one may load the cuvettes with as low as 150 uL of sample.
- Finally, the DWS RheoLabTM can be equipped with a particle sizing module to obtain the average size of colloids in a sample, in addition to rheology data.
Fig. 3: Illustration of the amplitude of moduli and frequency range of various rheology techniques.