A novel micro/nanoparticle hybrid calcium titanyl oxalate electrorheological (ER) material composed of micron-sized spindly particles and nanometer-sized irregular particles was successfully fabricated. The giant ER fluid based on the composite exhibits enhanced not only yield stress but also low field-off viscosity, thereby resulting in an ultrahigh ER efficiency that greatly exceeds that of any existing giant ER (GER) material. The synergistic effect between the spindly microparticles and irregular nanoparticles discovered in this study suggests a promising method for solving the long-standing ER efficiency problems. Moreover, the one-step synthesis approach presented in this work can be readily expanded for mass production of other GER materials in practical applications.

In this letter, we provide a phenomenological model to explain the recently discovered volume fraction effect in giant electrorheological (ER) fluids. We attribute the exponential dependence of yield stress on volume fraction to the repulsive interaction between particle chains. The increase of particle concentration increases the inter-chain repulsive interaction, which raises potential energy in electrorheological fluid and consequently the yield stress. The acquired normal force data validated our model.

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