Electro-rheological fluids (ERFs) are composed of a functional fluid and colloidal suspension. Their rheological properties vary rapidly and reversibly with the applied electric field intensity. ERFs are mixtures of nonconductive silicone oil and inorganic/organic composite electro-rheological particles. Investigations into the properties of ERFs have led to remarkable advances in their performance in recent years. However, ERFs exhibit an undesirable property that obstructs the long-term use of ERF devices, namely the sedimentation and separation of ER particles from the silicone oil. The sedimentation of ER particles reduces the electro-rheological effect. In order to suppress the sedimentation and thereby improve the performance of ERF devices, a new functional material called Gel Structured ERF (ERG) is developed and its basic properties are analyzed in this study. The ER particles are sustained in the gel component, and thus will not precipitate out. This suppresses the decrease in ER effect associated with precipitation. The developed ERG shows large shear stress variation in response to the applied electric field. This high performance of ERGs involves a different mechanism than that observed in ERFs. In order to elucidate the mechanism in ERGs, the behavior of ER particles was observed under an electric field. Conditions at the interface between the electrode and ERG were found to change rapidly in response to the applied electric field, resulting in the variation of shear force.
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