Study on Electric Properties of Particle/Fluid Suspension

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Materials of particles suspended in fluid are expected to change fluid properties and structures with an application of external electric and magnetic fields. Several properties of such fluid materials have been investigated experimentally and theoretically Electrorheological (ER) effects are typically observed in particle/insulating oil dispersions, whose shear stress can drastically increase with the external electric field applied. In the past, a number of mechanisms were proposed to explain such behavior. On the basis of the consideration of particle aggregation structures under the electric field, poor understanding of the mechanism makes it difficult to establish the grounding of material design of ER fluids. This project employed an ER fluid of silica particles or ferroelectric barium titanate particles suspended in electrically insulating silicone oil. In-situ measurements of dielectricity, electroconductivity and generated shear stress were performed under an application of alternative electric field. The generated shear stress was found to closely depend on the dielectric constant of the suspension. This finding has led to the derivation of a new correlation equation for the generated shear stress, the generated permittivity and the external electric field strength. It is verified that the equation can be applied for a wide variety of experimental conditions.