CAS Key Laboratory of Mechanical Behavior and Design of Materials, Department of Modern Mechanics, University of Science and Technology of China, Hefei, Anhui 230027, China.
Soft Matter. 2018 Jun 20;14(24):5080-5091. doi: 10.1039/c8sm00704g.
This work reported a simulation study on the optimal diameter (D) and wall thickness (H) of hollow Fe3O4 microspheres to improve the magnetorheological (MR) effect. Modified formulae for the magnetic dipolar force, van der Waals force, and hydrodynamic drag force were employed in the simulation model. Typical evolution of shear stress and microstructures in steady shear flow was obtained. The shear stress-strain curve was divided into linear, fluctuant, and homeostasis regions, which were related to the inclination of particle chains and the lateral aggregation. For hollow Fe3O4 microspheres with different diameters and wall thicknesses, the shear stress curves collapsed onto a quadratic master curve. The best wall thickness was H = 0.39D for a 20 wt% MR fluid and H = 0.35D for a 40 wt% MR fluid, while the optimal diameter was D = 1000 nm and D = 100 nm, respectively. The maximum shear stress of the 40 wt% MR fluid was twice that of the 20 wt% MR fluid. The change of shear stress was due to the competition that results among the magnetic interaction, number of neighbors, tightness, and orientation of the particle chains. Simulated dimensionless viscosity data as a function of Mason number for various diameters, wall thicknesses, and weight fractions collapsed onto a single master curve. The simulated shear stress under both a magnetic field and shear rate sweep matched well with experiments.
本工作报道了空心 Fe3O4 微球的最优直径（D）和壁厚（H）的模拟研究，以提高磁流变（MR）效应。模拟模型中采用了改进的磁偶极力、范德华力和流体动力阻力公式。获得了稳态剪切流中典型的剪切应力和微观结构演变。剪切应力-应变曲线分为线性、波动和稳态区域，这与颗粒链的倾斜和横向聚集有关。对于具有不同直径和壁厚的空心 Fe3O4 微球，剪切应力曲线在二次主曲线上重合。对于 20wt%MR 流体，最佳壁厚为 H=0.39D，对于 40wt%MR 流体，最佳壁厚为 H=0.35D，而最佳直径分别为 D=1000nm 和 D=100nm。40wt%MR 流体的最大剪切应力是 20wt%MR 流体的两倍。剪切应力的变化是由于磁相互作用、邻居数量、颗粒链的紧密程度和取向之间的竞争所致。各种直径、壁厚和重量分数的无量纲粘度数据作为马森数的函数的模拟数据在单个主曲线上重合。磁场和剪切速率扫描下的模拟剪切应力与实验吻合良好。
