Development of Transient Viscosity Measurement Method and Improvement of Polymer-Blended Electrorheological Fluids

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Since the observation of a large electrorheological (ER) effect in polymer blends of sidechain type polysiloxane liquid crystalline polymers (LCPs) and a dimethylsilicone (DMS) by Inoue et al, we have been making an intensive investigation to elucidate the mechanism. So far, we have clarified the fundamental mechanism of the polymer blend consisting of LCP droplets with high viscosity dispersed in DMS with low viscosity, which stretch and coalesce to from bridges between electrodes under an electric field, resulting in the increase of the apparent viscosity.This year we have investigated the transient process after applying a step electric field under shear flow by measuring the shear stress and the transmitted intensity through the sample at the same time. As a result, it was found that the transient process consists of two modes ; just after applying the field the stress steeply increases (the first mode) and then slowly increases (the second mode). From this result and observations with a high speed video camera, we concluded that the first mode corresponds to the stretch of droplets and the formation of bridges between electrodes, and the second mode to the growth of the bridge. In addition, we have performed computer simulations to investigate the deformation of the droplets under an electric field and/or a shear flow.Through the present project the the mechanism of ER effect in polymer blends have been clarified. On the basis of the obtained results ER fluids applicable to actual devices will be developed in the near future.