Structure factor of electrorheological fluids in compressive flow

Abstract

This paper examines the chain structure factor evolution of electrorheological (ER) fluids in compressive flow. The yield strength of ER fluids was modeled based on a single pair electrostatic interaction between particles and the structure factor, which includes all the effects except the single pair electrostatic interaction between particles presented by the local electric field strength between particles. Both the mechanical and electrical properties of ER fluids in compressive flow have been experimentally determined. The nominal shear yield stress of the ER fluid in compressive flow was derived by assuming that it was a transformed shear flow of a Bingham fluid. The single pair particle interaction strength is related to the measured electric current, which reflects the local electric field strength between particles. The structure factor evolution in compressive flow was derived by comparing the nominal shear yield stress and the single pair particle interaction strength. As expected, the calculated structure factor increased significantly using this method, much higher than that described by the many-body effect and the difference of dipole-dipole interaction and multi-dipole interaction between particles. Direct mechanical contacts and frictional forces between particles are thought to contribute significantly to the high structure factor and nominal shear yield stress of the ER fluid in compressive flow. This behavior might be similar in magnetorheological (MR) fluids.

Yield Hardening of Electrorheological Fluids in Channel Flow

“…In shear mode, shear-induced lamellar structures are known to form, while in flow mode, the suspension microstructure tends to contain clusters and aggregates [7][8][9]. In addition, an enhancement in the shear yield strength has been shown in magnetorheological fluids as the fluid is compressed in the direction orthogonal to shear [10] and a strengthening of the microstructure of ER fluids has also been shown in squeeze mode by Tian et al [11].…”

The normal stress of an electrorheological fluid in compression mode

“…23,24 By investigating the performance of ER uids subjected to compressive loading, EI Wahed found the imposed force was highly dependent on the applied voltage and the weight fraction of the dispersed solid-phase. 25 Liu et al studied the normal force of the ER uid employed for the haptic application, showing the application of the usage of compression mode.…”

“…During compression, the liquid owing through the gaps of particles produces a pressure to destroy or deform the chains structure. 24 For the ER particles, they experience a viscous force F vis acting by the liquid and interaction force F p from other particles. The particles will be squeezed out with the silicone oil from electrodes because of viscous force.…”

Polyaniline‐tailored electromechanical responses of the silver/epoxy conductive adhesive composites

“…Mixture of microscale and nanoscale particles or mixture of metallic and conductive polymer fillers has been used to improve the electrical conductivity of ECAs and to reduce cost . Conductive polymer composites have also been used in the development of smart materials and structures in which the conductive fillers can response to the external (electric and magnetic) fields by aligning to the field direction; the resultant anisotropic structures have a pronounced force‐dependent conductivity or piezoresistivity …”

“…1,5,6 Conductive polymer composites have also been used in the development of smart materials and structures in which the conductive fillers can response to the external (electric and magnetic) fields by aligning to the field direction; the resultant anisotropic structures have a pronounced force-dependent conductivity or piezoresistivity. 7 As illustrated in Figure 1, engineering applications of ECAs involve a compressive pressure (also called as compressive stress or Fz) and/or heat during the bonding of components, where the conductivity of the resultant bonds significantly depends on the pressure and heat. Figure 1 also depicts the typical morphology of conductive fillers: silver flakes, polyaniline (PANI) microparticles, and their chemical structure.…”