A Synergistic Electrorheological Enhancement by Adsorbed Surfactants and Water

Dielectric properties of surfactant activated alumina suspensions were investigated to probe the mechanism by which surfactants enhance the particle polarization. The dielectric constants of the surfactant adsorbed alumina particles indicate that the enhanced particle polarizability can not be the only effect of the adsorbed surfactants and there is a synergistic effect. Adsorption study showing that considerable amount of surfactants and water presents on the particles and the ER response increasing with the water content indicate that adsorbed surfactant and water interact cooperatively to enhance interfacial polarization. The observed gel structures of Brij 30 and water support this explanation. The ER response increases with the Cl^- content on the particles, supporting that the ER enhancement may arise from the increased proton transfer. Therefore, by forming a gel structure promoted by hydrogen bonds between the adsorbed surfactants and water on the particle surface, the dielectric properties of particles increases due to proton transfer through the gel structure, leading to the enhanced ER response.