VISCOELASTICITY OF
AN ELECTRORHEOLOGICAL FLUID
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VISCOELASTICITY OF |
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When an electric field is applied, an electrorheological (ER) fluid becomes highly anisotropic due to chain-like structures that align with the field. Measurements of viscoelasticity with non-disruptive, oscillatory strain give information about both the energy storage and energy dissipative capacity of this microstructure. The Vilastic ER cell is composed of two parallel conducting plates, separated by 0.875 mm thick insulating strips, forming a rectangular channel 51.0 mm long and 7.52 mm wide. The Vilastic VE System generates a longitudinal oscillatory flow in the channel. The shear stress, strain, and shear rate at the channel walls are determined from measurements of the oscillatory pressure and volume flow[1]. |
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For example, measurements of viscoelasticity were made with an oscillating strain of 0.6 at 2 Hz and 23 °C. The plot above shows the viscosity and elasticity of a 5 g% cornstarch suspension in mineral oil. A base line viscoelasticity of the fluid was established. Then the field was turned on suddenly at a strength of 914 Vdc/mm and held constant for a period of 2 min, after which the field was turned off. The DC field caused a rapid increase in the viscosity and elasticity followed by a slower increase through the remaining field-on period. When the field was turned off, the viscoelasticity decreased rapidly but did not return fully to the base line state during the remaining period of observation. The effects of either DC or AC fields can be measured with the VE System and ER cell In addition, viscous and elastic stress can be studied as a function of strain amplitude to reveal the breaking strength of the field induced microstructure. [1] G. B. Thurston and E. B. Gaertner, "Viscoelasticity of electrorheological fluids during oscillatory flow in a rectangular channel", Journal of Rheology, 35, 1327-1343 (1991).
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