Simulations of polydisperse magnetorheological fluids: A structural and kinetic investigation

Abstract

A simulation method is proposed to explore the effect of particle size polydispersity in magnetorheology including Brownian motion. The method aims to extend the classical particle-level simulation methodology developed by Klingenberg et al. [J. Chem. Phys. 91, 7888–7895 (1989)] for the case of polydisperse magnetorheological (MR) fluids. The simulation study concerns the aggregation kinetics at rest as well as the rheological behavior under start-up of steady shear and dynamic oscillatory shear tests at increasing strain amplitudes. Results demonstrate that the effect of polydispersity is only relevant at the transition regime between magnetostatic to hydrodynamic control of the suspension structure. The yielding behavior is correlated to the structural characteristics (radial distribution functions, pair correlation functions, and angular connectivities) of the MR fluids before the onset of flow. A more abrupt transition is observed for polydisperse MR fluids because interparticle links are weaker in this case if compared to monodisperse suspensions in spite of the fact that polydisperse MR fluids exhibit a larger connectivity.

Start-up rheometry of highly polydisperse magnetorheological fluids: experiments and simulations

“…Particle concentrations and size distributions explored are within the range of those of interest in commercial applications (clearly larger than that reported by Fernández-Toledano et al 2015). Special care is taken for the mean particle size of the distributions to remain constant (variations less than 5 %).…”

“…Expressions for the exponential forces used in this manuscript for continuous particle size distributions can be found in the work of Fernández-Toledano et al (2015).…”

“…. This velocity was found to provide a stress value close to the yield stress (Fernández-Toledano et al 2015). Simulations were composed of three stages: (i) Particles were randomly distributed in the simulation box, (ii) Particles were allowed to move under the presence of the magnetic field in quiescent state until reaching a stationary state.…”

Recent progress on the simulation technology of magnetic fluid

“…(a) Shear stress versus magnetic flux density curves of hollow Fe 3 O 4 MR fluid [20] ; (b) flow curves [20] ; (c) influences of particle diameter, wall thickness, and weight fraction on the apparent viscosity of hollow Fe 3 O 4 MR fluid [20] ; (d) the magneto-induced normal stress of magnetic fluid with different volume fractions and ratios of diamagnetic particles [80] ( ) 图 8 (网络版彩色)传统磁性液体复杂力学行为的数值模拟结果. (a) 磁性液体沉降前后的内部结构图 [82] ; (b) 多分散磁性液体连通性随时间的 演化 [83] Figure 8 (Color online) Simulation results of complex mechanical behaviors of conventional magnetic fluid. (a) Microstructures of magnetic fluid before and after settlement [82] ; (b) time-dependent connections between particles for polydisperse magnetic fluid [83] 取向在 θ~d θ θ + 范围内的相互接触的颗粒数:…”

“…(a) 磁性液体沉降前后的内部结构图 [82] ; (b) 多分散磁性液体连通性随时间的 演化 [83] Figure 8 (Color online) Simulation results of complex mechanical behaviors of conventional magnetic fluid. (a) Microstructures of magnetic fluid before and after settlement [82] ; (b) time-dependent connections between particles for polydisperse magnetic fluid [83] 取向在 θ~d θ θ + 范围内的相互接触的颗粒数:…”