Krishnamurthy V V, Bhandar A S, Piao M, Zoto I, Lane A M, Nikles D E, Wiest J M, Mankey G J, Porcar L, Glinka C J
Center for Materials for Information Technology, The University of Alabama, Tuscaloosa, Alabama 35487, USA.
Phys Rev E Stat Nonlin Soft Matter Phys. 2003 May;67(5 Pt 1):051406. doi: 10.1103/PhysRevE.67.051406. Epub 2003 May 23.
Small-angle neutron scattering experiments have been performed to investigate orientational ordering of a dispersion of rod-shaped ferromagnetic nanoparticles under the influence of shear flow and static magnetic field. In this experiment, the flow and flow gradient directions are perpendicular to the direction of the applied magnetic field. The scattering intensity is isotropic in zero-shear-rate or zero-applied-field conditions, indicating that the particles are randomly oriented. Anisotropic scattering is observed both in a shear flow and in a static magnetic field, showing that both flow and field induce orientational order in the dispersion. The anisotropy increases with the increase of field and with the increase of shear rate. Three states of order have been observed with the application of both shear flow and magnetic field. At low shear rates, the particles are aligned in the field direction. When increasing shear rate is applied, the particles revert to random orientations at a characteristic shear rate that depends on the strength of the applied magnetic field. Above the characteristic shear rate, the particles align along the flow direction. The experimental results agree qualitatively with the predictions of a mean field model.
已进行小角中子散射实验，以研究在剪切流和静磁场影响下棒状铁磁纳米颗粒分散体的取向有序性。在该实验中，流动方向和流动梯度方向垂直于外加磁场方向。在零剪切速率或零外加场条件下，散射强度是各向同性的，这表明颗粒是随机取向的。在剪切流和静磁场中均观察到各向异性散射，这表明流动和磁场都能在分散体中诱导取向有序。各向异性随磁场增强和剪切速率增加而增大。在同时施加剪切流和磁场的情况下，观察到了三种有序状态。在低剪切速率下，颗粒沿磁场方向排列。当施加的剪切速率增加时，颗粒在取决于外加磁场强度的特征剪切速率下恢复为随机取向。在特征剪切速率以上，颗粒沿流动方向排列。实验结果与平均场模型的预测在定性上相符。
