Brookfield R/S-SST Rheometer - Manual (Page 7)

BROOKFIELD
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Typical results plot:
Creep test on fruit conserve.
Angular displacement (Phi,
radians) is plotted against time.
Short timescale response relates
to elastic behaviour and long
timescale response relates to
viscous behaviour. So a high
initial angular displacement
indicates a flexible “wobbly” gel
structure while a steep gradient at
long timescales means a product
that creeps easily, that is, it has a
low low-shear viscosity.
A Few Tips To Get You Started
It is important to operate the SST2000 at torque values that are within the SST2000’s
reliable range of 30
%
0
(3% or 1.5mNm) to 1000
%
0
(100% or 50mNm). In creep
testing the minimum recommended applied torque is 75
%
0
(3.75mNm).
If you prefer to work in stress values then these torques equate to the following for
our standard vanes:
Constant Rate Test Creep Test (recommended minimum)
V30-15 121 Pa to 4040 Pa 303 Pa
V40-20 51 Pa to 1700 Pa 128 Pa
V80-40 6.4 Pa to 213 Pa 16 Pa
Vane selection
The first consideration in vane selection is the working torque ranges just mentioned.
The next consideration relates to vane-to-container diameter ratios. The vane
measuring method works best when these ratios are lower than 0.75. Low
vane/container ratios allows us to measure samples with large particulates dispersed
throughout and we can also apply low strains to our sample while still operating at
angular displacements well within the instrument range.
Ideally, the vane should be immersed in a sample of a depth twice that of the vane
height. This is, however, very often not practical but the user should at least ensure
ample clearance between the lower end of the vane and the base of the container,
especially when measuring large-particle suspensions.