Effect of pollution on the interfacial properties of electrorheological fluids

The influence of liquid and solid polluting agents on the interfacial properties of electrorheological (ER) fluids, systems whose viscosity noticeably increase under the action of electric field with very low power consumption, has been evaluated. Hematite/silicone oil dispersions were considered as the reference ER sample that was contaminated by water as well as iron and iron-silica composite particles to examine the modifications of its performance that moisture and the degradation of metallic and other pieces of ER-based devices produce, respectively. Additionally, the effect of surfactants and plasticizers – used to promote the stability of suspension – on the viscosity and electric current of ER fluids was tested as well. It was observed that liquid polluting agents always enhanced the electric current leaking through the ER suspension even by several orders of magnitude depending of their conductivity. What is more, short-circuits appeared at relatively low concentrations of these pollutants and low field strengths. Similarly, the viscosity of polluted samples also resulted to be enhanced but this only occurred at very small amounts of liquid polluting agents. This fact could be related to the cohesive forces appearing between particles due to the formation of liquid bridges among them. Furthermore, it was found that the rheological properties of the samples were also altered by the way the stabilizers were incorporated into the suspensions. When these liquids were directly added to the host oil instead of the solid phase, a net reduction of the ER response was observed. On the other hand, it could be observed that the most pernicious effect of the presence of metallic and/or slightly conductive particulates in ER fluids was not a net change of their flow and conduction properties, but the occurrence of short-circuits at very low amounts of these particles, no matter the magnitude of the applied field—eliminating therefore any practical use of the ER fluid. In summary, important conclusions from this study can be extracted to preserve the functionality of ER fluids and their possible applications.