Abstract
The electrorheological (ER) effect was experimentally observed in dielectric suspensions containing tungsten oxide (WO3) modified with surfactant molecules (sodium dodecyl sulfate (SDS) and dodecylamine (DDA)) in electric fields up to several kilovolts per millimeter. The dielectric properties of WO3 suspensions in silicone oil were analyzed, depending on the frequency of the electric field, in the range from 25 to 106 Hz. Unmodified WO3 suspensions, as well as suspensions modified with sodium dodecyl sulfate, were shown to exhibit a positive electrorheological effect, whereas suspensions modified with dodecylamine demonstrated a negative electrorheological effect. The quantitative characteristics of the negative electrorheological effect in the strain–compression and shear regimes were obtained for the first time. Visualization experiments were performed to see the chain structures formed by WO3 particles modified with sodium dodecyl sulfate, as well as for dynamic electroconvection in electrorheological fluids containing WO3 modified with dodecylamine. The negative electrorheological effect was shown to be associated with the processes of phase separation in the electric field, which led to a multiplicative effect and a strong electroconvection of the suspension at field strengths above 1 kV/mm.
Highlights
The development of stimuli-responsive materials capable of changing their physical properties in response to external factors such as temperature, pH, light, mechanical loads, and electromagnetic fields is of considerable interest, both to applied and to fundamental science [1,2,3,4,5,6,7]
Quantitative characteristics of viscoplastic properties for electrorheological fluids containing tungsten oxide fillers, including filler particles modified with surfactants, were obtained in strain, compression, and shear tests in electric fields up to 5 kV/mm in polydimethylsiloxane PMS-300
An increase in the strength of the applied electric field led to an increase in the strength characteristics of the abovementioned ER fluids, namely, shear stress, compressive stress, and strain tension
Summary
The development of stimuli-responsive materials capable of changing their physical properties in response to external factors such as temperature, pH, light, mechanical loads, and electromagnetic fields is of considerable interest, both to applied and to fundamental science [1,2,3,4,5,6,7]. A special place among such materials is occupied by liquid systems that reversibly change their physical and mechanical properties in magnetic and electric fields—namely, magnetic, magnetorheological, and electrorheological (ER) fluids [8,9,10,11]. Most devices of practical interest are based on a positive electrorheological effect, such as ER clutches, brakes, damping devices, hydraulic valves, shock absorbers, robotic controlling systems, gripping devices, seismic controlling frame structures, human muscle stimulators, and spacecraft deployment dampers [12]
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