The role of water in electrorheological fluids

The role of water in ER (electrorheological) fluid systems is investigated by correlating its physical state with the rheological properties of the fluid. In particular, the suitability of the water bridging model of the ER effect is evaluated. The electrorheology of three model fluids was studied as a function of electric field strength, moisture content, and placement under dynamic oscillatory shearing. It has been demonstrated that an ER fluid with a porous hydrophilic dispersed phase may behave very similarly to one with a nonporous hydrophobic dispersed phase. A novel ER fluid was prepared using a microencapsulated dispersed phase containing an abundance of water. It was found that although water was present in large amounts, as long as it was segregated from the continuous interparticle environment, the ER effect was greatly diminished from what one would expect based on this criterion alone. The results are in agreement with the idea that interparticle bridging by water may be an important aspect of the ER effect