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Rheology - Geometries

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Geometries - Pros and Cons

Text books contain a huge selection of geometries for your rheometer. But what should you buy? With a simple geometry costing in excess of €500 you want to buy what you are actually going to use and you simply can't afford to buy everything.

Cone and Plate

Pros:

Rheologically correct because the angled cone gives an even shear Field.

Cons:

You can't alter gap.

If you use for heating experiments the sample drying out is a problem. Our recommendation is to add oil and a solvent trap.

You shouldn't use if your sample has particles greater than 1/10 the gap distance. The gap distance is typically 50u

Cone and Plate

Parallel Plate

Pros:

You can alter the gap which is useful if you have small particles in your sample or you want to change the shear rate range significantly.

Very popular in industry due to its flexibility.

Cons:

Rheologically shear varies across plate so its not as rheologically correct as the cone and plate.


 

Plate

Concentric Cylinder / Bob and Cup

Pros:

One of our favourite geometries. Rheologically correct and very useful for temperature sweeps as the small exposed surface area gives little evaporation and practiaclly none with a thin layer of oil added.

Cons:

Somewhat messier to clean.

You probably cannot run temperature ramps as fast as you can on a plate or cone.

Bob and Cup

Double Gap Cylinder

Pros:

The idea behind this geometry is to incease the low stress measurement capability compared to a standard concenric cylinder.

Cons:

You probably have about double the surface area compared to a similar concentric cylinder. So a similar torque translates to double the stress. It sounds a lot but when most rheological curves are plotted with log-stress then it doesn't actually gain you as much as you might think.

Somewhat messier to clean.

You probably cannot run temperature ramps as fast as you can on a plate or cone.

Double Gap Cylinder