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The rheology group used a micro-optic apparatus called the Cambridge
Shearing System to shear the PDMS and PIB emulsion drops. During
each run, an emulsion drop was suspended between two horizontal,
parallel plates that move back and forth. The scientists performed
both simple shear and oscillatory shear measurements on the drop.
During the simple shears, the drop was sandwiched between two plates
that slide horizontally. Renardy likens the movement to an "infinitely
large knife putting mayo on infinitely long bread." The oscillatory
shears mimicked the movement of the knife being drawn back and forth
across the bread. The scientists sheared the drop by oscillating
the plate to the right, then to the left, reversing the direction
with a given period, such as every three seconds.
The rheology group then provided Renardy with the experimental
data for both types of shears. Through direct numerical simulations,
the scientists hoped to obtain corroboration that the empirical
measurements were correct. It may sound strange that scientists
would seek theoretical corroboration to confirm the accuracy of
empirical data. However, experimentalists often worry that the forces
they are observing may not be due to the theoretical flow they have
in mind. Therefore it is helpful to have their data checked against
numerical simulations detailing the proposed theoretical flow. Corroboration
gives them some confidence that their data is correct and not due
to other forces that they have not considered.
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