Abstract:
Research has been undertaken into the dielectric and rheological properties of
electrorheological (ER) fluids. The fluids studied were based on acene-quinone radical
polymers made within the department dispersed in silicone oil. A commercial
poly(1ithium methacrylate) dispersion was also examined.
As a means of
probing the underlying mechanisms of the E phenomenon, the
permittivity of the fluids was measured from 12 Hz to 100 kHz under both static and
dynamic conditions. Results indicated that a interfacial polarization process was taking
place.
A series of visual observations were made of fluids under different fielding patterns.
A series of
photographs were taken that illustrated the structure formation with elapsed
time in a dilute fluid. Also photographs were taken of the final structure formed under
different field conditions. ..
To
perform permittivity measurements of the fluid when a electric field was applied,
a
high voltage biasing unit was designed, built and proved. This allowed the application
of a continuous DC electric field of up to 3 kVmm" and the permittivity to be
measured from 150 H t 100 kl-Iz. Through a series of experiments it was found that
the low
frequency permittivity increased with increasing electric field. This result was
partially explained by the Sillars model.
The fluids were also subjected to shear rates from 1500 to 60 s". Flow modified
permittivity resonances were found at the predicted frequencies. However, the resonant
frequency did not move significantly under the application of a electric field.
The
structuring process was time resolved and a model was made to predict the sealing
of the characteristic structuring time. The rheological response of the fluids when
subjected
t pulsed DC fields was examined and found to be dominated by a
instrumentational effect.
Al
experimental procedures are given along with a comprehensive examination of the
equipment. The results are discussed as they occur in terms of the models appropriate
to that
particular event.
