Brookfield DV3T Rheometer User Manual
Page 90
Brookfield Engineering Labs., Inc.
Page 90
Manual No. M13-2100
An Example of the Casson Model at Work
Before releasing a new over the counter gel, a
pharmaceutical company needs to learn how
it will behave which it is being used by the
end consumer. They perform a full viscosity
profile and apply the Casson model. From the
results, shown in Figure VII-4, they learn that
their ointment has a higher yield stress, τ
o
, and
lower plastic viscosity,
h
, than they originally
intended. As a result it is difficult or dispense from its container (due to the high yield stress)
and it does not hold it shape very well (due to the low plastic viscosity), making it difficult to
apply a small amount to the affected area of the skin. Based on this data, formulators are able
to modify the ingredients accordingly. Once a formulation is established, multi-point tests and
the Casson model are performed as a QC tool to check batches before and after processing.
Pharmaceutical Gel
Plastic Viscosity (
h
) = 329.8 cP
Yield Stress (τ
o
) = 325.8 dynes/cm
2