Influence of surfactants on properties of electrorheological fluids containing polyaniline

Sedimentation which is a natural process in most of ER fluids can be reduced by addition of surfactants that influence also other properties of the fluids. To study both the ER effect and the rate of sedimentation was the aim of the investigations. The ER fluids comprised powdered polyaniline and silicone oil to which surfactants of different polarity were added. The rate of sedimentation was measured by a sedimentation balance. The flow curves were recorded under electric field up to 2.5 kV/mm. Current density was also measured as a function of shear rate. It was found that the activity of a surfactant depends strongly on its polarity. The lipophylic surfactants stabilized the suspension very well but about 30% decrease of the dynamic yield stress was observed The current density was reduced as well by almost one order of magnitude The hydrophylic surfactants hardly stabilized the suspension but increase of yield stress was observed that was not followed by increase of current density. The role of different types of non-ionic surfactants was discussed.