Giant electrorheological fluids with ultrahigh electrorheological efficiency based on a micro/nano hybrid calcium titanyl oxalate composite

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. A material that can alternate between a low-viscosity fluid and a strong solid has been developed by researchers in China and the USA. Applying an electric field to an electrorheological fluid transforms it from a fluid to nearly solid state, and removing the field changes it back to a fluid; but the application of a small stress can irreversibly deform such materials. Yuchuan Cheng, Shengqian Ma and co-workers from the Ningbo Institute of Materials Technology & Engineering and the University of South Florida have used a simple one-step process to synthesize a composite electrorheological material that has a high yield strength. The composite contains spindly microparticles, which ensure a low viscosity when there is no electric field, and irregular nanoparticles, which enhance its yield strength. These two properties impart the composite with ultrahigh electrorheological efficiency. Hybrid calcium titanyl oxalate (HCTO) composite containing anisotropic spindly microparticles and irregular nanoparticles have been synthesized via a facile precipitation route under mild conditions for the first time. The hybrid particles act synergistically to enhance electrorheological (ER) activity and reduce field-off viscosity, thereby resulting in ER fluids with ultrahigh ER efficiency. The results presented thus provide a new strategy for improving the performance of ER fluids.