HIGH AC VOLTAGE FLOW-MODIFIED PERMITTIVITY AND RHEOLOGICAL PROPERTIES OF CARBON-DOPED NANO TiO2 ER FLUIDS

The associated effects of polarization strength, polarization rate, and dielectric loss on ER performance ware studied by means of the correlation of rheological properties of carbon-doped TiO 2 ER fluids with experimental results of flow-modified permittivity (FMP). We prepared ER fluids with carbon-doped TiO 2 powders of different conductivity via controlling carbonization temperature and organic contents. The experiments present the optimum organic contents of 4.6% to 9.2% and the optimum carbonization temperature of around 673 K for the better ER activity. The role of conductivity in ER performance is testified. FMP measurements of fluids were performed under weak and strong exciting fields respectively. Under weak exciting field, FMP effects are hardly detectable; while under high exciting field, FMP effects become significant which reflect ER particle configurations, particle orientations, and limited dielectric response time in the combined electric and shear fields. The shear field strength, exciting field strength and frequency are the three main factors influencing the FMP effects. The FMP data can be modeled and qualitatively explained by introducing two characteristic shear rates of D c 1 and D c 2, J = J 0+ J 1 exp (- D / D c 1)+ J 2 exp (- D / D c 2) with D being shear rate.