When a sufficiently strong electric field is applied to certain fluid, they undergo marked changesin their rheological properties. Such fluids have come to known as electrorheological fluid. Materials used in this study are polyaniline in mineral oil and corn starch in corn oil. In this thesis, in order to understand the physics governing the ER effect and to develop a semi-conducting polymer based ER fluid, an experimental investigation was done for the steady shear behavior, dynamic properties were measured as functions of driving frequency, shear rate, and electric field strength. Polyaniline was synthesize using the method of bulk polymerization of aniline. The formation of particle strand columns under the electric field was observed. Formation of the chain structure is so faster that it is hard to be noticed when it is formed. However continuous rearrangement of the particles can be seen extended period of the particles can be seen extended period of time after the initial formation of the chain structure. As increase of the electric field strength to 2 kV/mm for corn starch ER fluid, particle strings has been highly bridge and the particle distribution was saturated to one electrode. For polyaniline suspension, as increase of the electric field to 2.0 kV/mm, there is no saturation effect as shown in corn starch suspension but nearest particle strings approached to next particle string and attached. Thus, the continuos(suspending medium) phase between the strings was broaden.
The steady shear and viscoelastic behavior of polyaniline suspension in mineral oil subjected to electric field were experimentally using Couette cell type rheometer. The yield stress determined from the plateau stress at low shear rate was evaluated as a function of the applied field strength and particle volume fraction. The resultant yield stress is linearly increased with volume fraction and $E^\frac{3}{2}$, which may imply that there exist charge carriers in polyaniline particles. The storage shear and loss moduli have been measured using strain amplitude force oscillatory dynamic test as functions of strain amplitude, driving frequency, and the applied field strength. The linear viscoelastic region was found to be as below 0.01 of strain amplitude by performing the amplitude sweep test. The storage shear and loss moduli were strongly dependent upon strain amplitude while those were nearly independent of the driving frequency of $10^{-1}~10^2 rad/s$. The nonlinear viscoelasticity are observed with not only increasing strain amplitude but also increasing driving frequency.
The suspension of polyaniline and corn starch show drastic increase in the steady viscosity on the application of electric field. For polyaniline suspension, there is reasonable agreement between the values of the dynamic yield stress obtained with CSR test and the static yield stress obtained with CSS test. Thus, there is only a static yield stress and no dynamic yield stress for polyaniline ER fluid with the electric field.
For corn starch suspension, especially the static yield stress is larger than the dynamic yield stress below the $E=2.0 kV/mm$.
At low stress, the creep and recovery curve comprises instantaneous strain, retardation strain, and permanent strain. The permanent strain is due to viscous flow and not recovered. The elastic limit stress increased with increasing of electric field strength. At very small strain, linear dependency between the stress and strain obtained like solid behavior.
The ratio of strain recovery to total strain decreased with increasing imposed field. Thus when the stress approach the static yield stress, the plastic tendency become striking.
