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Abstract
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.
Highlights
Electrorheological (ER) fluids, which exhibit flow behavior and rheological properties that can be tuned in a controlled manner using an external electric field, are some of the most attractive smart materials.[1,2] ER fluid is generally a suspension consisting of polarizable particles dispersed in a nonpolar liquid medium
Various inorganic and organic/inorganic giant ER (GER) materials have been synthesized;[18,19,20,21,22,23,24,25,26,27] for example, Wen et al.[18] reported a new type of GER fluid consisting of polar group-modified nano-sized barium titanyl oxalate particles suspended in silicone oil
hybrid CTO (HCTO) particles were synthesized via the simple co-precipitation of tetrabutyl titanate, calcium chloride and oxalic acid
Summary
Electrorheological (ER) fluids, which exhibit flow behavior and rheological properties that can be tuned in a controlled manner using an external electric field, are some of the most attractive smart materials.[1,2] ER fluid is generally a suspension consisting of polarizable particles dispersed in a nonpolar liquid medium. Applying an external electric field changes ER fluid from a liquid to a nearly solid state within milliseconds, with an accompanying orders of magnitude increase in yield stress and shear modulus; this effect completely and rapidly reverses once the field is removed.[3,4,5,6,7,8] These features have made ER fluids the focus of numerous scientific investigations because of their potential application for actively controlling various devices with electric–mechanical interfaces.[9,10] Coupled with sensors to trigger the external electric field, ER fluids can turn many devices, such as clutches, valves and dampers, into active mechanical elements that are capable of responding to environmental variations. The polarization of molecular dipoles in the contact region between two neighboring nanoparticles is thought to be responsible for the GER effect.[15,16,17] Various inorganic and organic/inorganic GER materials have been synthesized;[18,19,20,21,22,23,24,25,26,27] for example, Wen et al.[18] reported a new type of GER fluid consisting of polar group-modified nano-sized barium titanyl oxalate particles suspended in silicone oil
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