Sedimentation behaviour in electrorheological fluids based on suspensions of zeolite particles in silicone oil.

Sedimentation is a known and expected shortcoming of electrorheological fluids (ERFs) due to the inherent difference in the constituent densities. The long-term sedimentation causes loss of the electrorheological phenomenon and the exploitable electromechanical and viscoelastic properties despite the presence of the stimulating electric field. In this work, we report the effect of temperature and surfactant concentration on the stability of ERFs prepared from zeolite particles and silicone oil with primary focus on the sedimentation of the particles in the ERF. As the temperature stability of the ERFs is fundamentally important, we have studied three different ERF suspensions composed of different zeolite particles, in silicone oil. These ERFs have been comparatively evaluated for their sedimentation over time, across a wide range of temperatures (-40°C to +60°C). The influence of surfactant concentration on the colloidal stability of the ERFs has also been investigated. A novel method of acoustic stirring (kHz range) on the homogenisation of the ERFs has been proposed and its effect on the sedimentation process evaluated. These results are useful for assessment of alternative suspension methods for specific applications.