TA Instruments AR 2000, Operator'S Manual, Page: 65 / 144

AR 2000 Operator's Manual
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Figure 6.11
Loading the Sample
Ensuring that the Sample is Loaded Correctly
Ensuring that the sample is loaded correctly and the gap is properly filled is probably one of the most important
points to consider in any rheological experiment.
You will find that you will become quite adept at
judging the right amount of sample to use, de-
pending upon the geometry diameter and gap
size. You can either calculate the exact volume or
weight of sample needed. However, care must be
taken if you intend to use a pipette or syringe to
deliver the correct amount. Samples that are
delicately structured will be adversely affected by
the high shear rate regime encountered in syringes
or pipettes. If the gap is not filled correctly, there
are certain types of errors that can occur. The
magnitude of the errors will be entirely sample
dependent, but generally over filling is less of a
problem than under filling. Such errors are called
edge effects . Figure 6.11 shows the different types
of filling encountered.
• If the gap is overfilled , some of the excess
sample may migrate to sit on top of the
geometry. If, however, the sample is of low
viscosity, this is not likely to happen and the errors are reduced.
• If the gap is underfilled , you are effectively altering the diameter of the geometry. This will inevitably
introduce large errors and you should definitely avoid this situation.
Loading the sample correctly is a skill that is learned with time. It may help you to spend some time initially
simply loading and reloading a sample. The correct loading is vital to accurate and meaningful results.