Abstract
Micro-capsules composed of poly(methyl metacrylate) (PMMA) or poly(vinyl acetate) (PVAC) as core materials, and silica as wall material were produced by sol-gel process. PMMA or PVAC emulsions were covered with silica derived from tetraethoxysilane by sol-gel process, and microcapsules with diameter of about 10-30 μm were obtained. These micro-capsules were dispersed in silicone oil with concentration of 30 wt% to prepare electro-rheological (ER) fluid. When DC or AC electric fields were applied on these fluids, the shear stress of the system increased, and ER effect was observed. In the case of PMMA micro-capsule, the shear stress of the system under AC electric field increased with shear rate, and higher than that under DC electric field. PVAC micro-capsule/silicone oil fluid showed Bingham flow under DC electric field, and shear stress was higher than that of PMMA system. PVAC micro-capsule/silicone oil system showed the dip behavior under AC electric field at higher shear rate region of 540-600 s-1 caused by destruction and reformation of the structure, and the stress was lower than that of PMMA system above 150 s-1. Organic-inorganic micro-capsules produced by the sol-gel process were effective dispersoids for ER fluid.
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