Many chemists who are experts on their chemical substance struggle to find relevant published rheology results. Whether for data comparison or for project development, you can’t expect a quick Google Scholar search to give you a simple answer for viscosity or other rheological characteristics. Unless you are seeking basic information on the rheology of cheeses, laponite suspensions, or wormy micelles, ditch the “rheology of [insert very specific chemical here]” search and save yourself time by using the following strategy to find applicable information.
The best way to go about gathering rheology information on a complex or novel material is to first consider what board class of substances it belongs to in terms of physical properties. Here are some examples of these general rheology categories: dilute solutions, concentrated solutions, emulsions, colloidal suspensions, colloidal gels, chemically crosslinked gel, soft material composite, film, and foam, among others.
Rheology textbooks give examples of classic rheological behaviors for a variety of substances. Identify which general rheology behavior your sample exhibits, and read about why those behaviors occur. Shear thinning, for instance, can be caused by structural breakup or alignment of particles, while moduli crossovers over time may signify hardening and crosslinking.
Also, investigate sources focused on the wider category of your sample. For example, if you wanted to find information on blood rheology test methods but do not have any biological rheology sources, the best place to start would be to look at emulsion rheology basics since whole blood is like an emulsion. Then you can look at emulsion data with concentration of cells in blood and emulsion droplet sizes similar to that of red blood cells as an approximation of the behavior of blood. Although it is not a perfect comparison, it gives you a starting point for your experimental design and a basis for identifying if your data is on the right track.
If working with multi-component gels, consider all of the main components – matrix material, particulates, crosslinker, and solvent. Look for sources for related substances. Even if the chemistries are vastly different, if the material has the same type of crosslinking (covalent, ionic, etc.) and similar-sized particles (nanoscale, microscale, or larger), the source can give general rheology insights to what to expect from your sample. In this manner, the rheology of some cosmetics is quite similar to the rheology of cement pastes – and the number of sources of relevant information is much larger!
As always, make sure to take into account temperature, test method, and sample preparation from published data. If your sample is not mixed or aged like the reference article, congruent results are highly unlikely. Often for colloids and gels the complex sample preparation steps listed in a publication are necessary for either repeatability or application relevance. If needed, compare articles with different sample preparation, noting if a pre-shear step was applied or if the sample was allowed to sit for a long time prior to conducting the rheometry measurement.
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