Abstract:
Electrorheological (ER) fluids are known to exhibit enhanced viscous effects under an electric field
stimulus. The present article reports the hitherto unreported phenomenon of greatly enhanced thermal
conductivity in such electro-active colloidal dispersions in the presence of an externally applied electric
field. Typical ER fluids are synthesized employing dielectric fluids and nanoparticles and experiments are
performed employing an in-house designed setup. Greatly augmented thermal conductivity under a
field’s influence was observed. Enhanced thermal conduction along the fibril structures under the field
effect is theorized as the crux of the mechanism. The formation of fibril structures has also been
experimentally verified employing microscopy. Based on classical models for ER fluids, a mathematical
formalism has been developed to predict the propensity of chain formation and statistically feasible
chain dynamics at given Mason numbers. Further, a thermal resistance network model is employed to
computationally predict the enhanced thermal conduction across the fibrillary colloid microstructure.
Good agreement between the mathematical model and the experimental observations is achieved. The
domineering role of thermal conductivity over relative permittivity has been shown by proposing a
modified Hashin–Shtrikman (HS) formalism. The findings have implications towards better physical
understanding and design of ER fluids from both ‘smart’ viscoelastic as well as thermally active materials
points of view.
