## Rheometer Rheometer is an useful tool dealing with viscoelastic related properties. After a sample being loaded, the rheometer would apply external strains or forces to the sample, and the mechanical responses from the sample get recorded. Based on different models (e.g., [[Mechanical response of colloidal system#Parameters and linear behaviors|Newtonian fluid]], [[Mechanical response of colloidal system#Herschel-Bulkley fluid|Herschel-Bulkley fluid]]), mechanical properties could be fitted and calculated. ### Structures The following sketch shows the structure of a typical rheometer. Samples are loaded on the Peltier plate, which is a temperature-adjustable sample loading stage. The geometry also the Peltier plate are replaceable parts. When removing (and after removing) Peltier plate, always check the connections of the stage. ![[Drawing 2023-11-10 01.06.09.excalidraw.svg]] ### Geometry Rheometer has different geometries, which are replaceable parts connected to the stress/strain sensor. For typical measurements, we use absolute geometries. These geometries are well defined and follow some standard. Most commonly applied absolute geometries include: - Concentric cylinder, CC This is a geometry able to measure all types of fluid, with large contact area. This gives higher precision for low viscosity/small strain cases. It is also called *Taylor–Couette* geometry (for it applies Taylor–Couette flow for measurements), or *Cups and Bobs* geometry. - Cone-and-plate, CP This is a geometry able to measure fluids and viscoelastic materials. The contact area is relatively big, and the angle (in some case) compensates radius change inside the gap. - Parallel-plates, PP Parallel plates may be used to measure fluids and viscoelastic materials. The gap could be big, which is preferred for viscoelastic materials. There is no angle, so along the radius mechanical properties would change. - Double gap, DG Double gap provides very large contact area ![[Drawing 2023-11-06 16.27.37.excalidraw.svg]] There are also other possible measuring systems under ISO standard. Also, for specific fluids, relative measuring systems may be applied. They could be spindles, balls, or stirrers, etc. Check [the page](https://wiki.anton-paar.com/en/rheometer-geometries-relative-measuring-geometries/) for more information on geometries. When samples are less viscous, at small strain(shear) rate, low-torque limit would be easier to be reached, and generate inaccurate viscosity data. These parts should be marked and indicated so that the corresponding viscosity data is not applied. ### Temperature control Rheometers allow users to perform measurements in different temperatures. This is done by the Peltier plate. Cooling is based on thermoelectric effect, i.e., Peltier effect. The Constant (room) temperature is provided by a water bath. Therefore, always remember to turn water bath on before using. If the water bath is not connected, Peltier elements could easily get overheat. >[!Info] >See also: >https://wiki.anton-paar.com/en/rheometer-geometries-relative-measuring-geometries/ >and manufacturer wiki: >Rheometer basics: https://wiki.anton-paar.com/en/basics-of-rheology/rheological-measurements/ >Geometry: https://wiki.anton-paar.com/en/rheometer-geometries-relative-measuring-geometries/ >Articles list: https://wiki.anton-paar.com/en/articles/