School of Mathematical, Physical Sciences and Computational Sciences, University of Reading, Reading RG6 6AX, United Kingdom.
Phys Rev E. 2018 Mar;97(3-1):032610. doi: 10.1103/PhysRevE.97.032610.
While magnetic nanoparticles suspended in Newtonian solvents (ferrofluids) have been intensively studied in recent years, the effects of viscoelasticity of the surrounding medium on the nanoparticle dynamics are much less understood. Here we investigate a mesoscopic model for the orientational dynamics of isolated magnetic nanoparticles subject to external fields, viscous and viscoelastic friction, as well as the corresponding random torques. We solve the model analytically in the overdamped limit for weak viscoelasticity. By comparison to Brownian dynamics simulations we establish the limits of validity of the analytical solution. We find that viscoelasticity not only slows down the magnetization relaxation, shifts the peak of the imaginary magnetic susceptibility χ^{″} to lower frequencies, and increases the magnetoviscosity but also leads to nonexponential relaxation and a broadening of χ^{″}. The model we study also allows us to test a recent proposal for using magnetic susceptibility measurements as a nanorheological tool using a variant of the Germant-DiMarzio-Bishop relation. We find for the present model and certain parameter ranges that the relation of the magnetic susceptibility to the shear modulus is satisfied to a good approximation.
虽然近年来已经对悬浮在牛顿溶剂（铁磁流体）中的磁性纳米粒子进行了深入研究，但对于周围介质的粘弹性对纳米粒子动力学的影响，人们的了解要少得多。在这里，我们研究了一个介观模型，用于研究在外部场、粘性和粘弹性摩擦以及相应的随机扭矩作用下孤立磁性纳米粒子的取向动力学。我们在弱粘弹性的过阻尼极限下对模型进行了分析求解。通过与布朗动力学模拟的比较，我们确定了解析解的有效性范围。我们发现，粘弹性不仅会减缓磁化弛豫，将虚磁导率 χ^{″}的峰值移至较低频率，并增加磁流变性，而且还会导致非指数弛豫和 χ^{″}的展宽。我们研究的模型还允许我们使用磁导率测量作为纳米流变学工具，使用 Germant-DiMarzio-Bishop 关系的变体来测试最近的一项建议。我们发现，对于当前模型和某些参数范围，磁导率与剪切模量之间的关系在很大程度上得到了满足。
