TA Instruments AR 2000, Operator'S Manual

Page: 117 / 144

AR 2000 Operator's Manual
117
7. Determine the point at which the normal force passes through zero. This is the position of the interface,
which should be at a gap of approximately 19500 µm. Adjust the fluid volume to obtain this gap. Keep in
mind that 1 mL of fluid changes the level by about 0.275 mm.
8. When the interfacial position has been identified, manually set the gap to that position (in the example
shown on the previous page, to 19527 µm).
9. Lift and fix the lid. You may find it convenient at this stage to add any surfactants to be used.
10. After addition of surfactant, gently add the less dense fluid until the lower edge of the groove on the top of
the cup is just covered, then lower the lid gently. The upper fluid should just enter the annular gap between
the lid and the geometry shaft. The viscosity of the total system including the interface can now be mea-
sured.
11. Run the Flow procedure used to determine the contributions of the two bulk fluids, described above, to
obtain the total torque M
total
(
Ω
).