Department of Applied Physics, University of Granada, Avenida Fuentenueva s/n, 18071, Granada, Spain.
J Phys Condens Matter. 2011 Nov 16;23(45):455101. doi: 10.1088/0953-8984/23/45/455101. Epub 2011 Oct 26.
This paper reports the preparation of magnetic fluids consisting of magnetite nanoparticles dispersed in an ionic liquid. Different additives were used in order to stabilize the fluids. Colloidal stability was checked by magnetic sedimentation, centrifugation and direct observation. The results of these tests showed that a true ferrofluid was only obtained when the nanoparticles were coated with a layer of surfactant compatible with the ionic liquid. These experiments also showed that stability could not be reached just by electrostatic repulsion. The conclusions of the stability tests were confirmed by calculations of the interparticle energies of interaction. The rheological behaviour of the magnetic fluids upon magnetic field application was also investigated. The experimental magnetoviscous response was fitted by a microstructural model. The model considered that the fluids consisted of two populations of particles, one with a magnetic core diameter of 9 nm, and another with a larger diameter. Upon field application chain-like structures are supposed to be induced. According to estimations particles of 9 nm are too small to aggregate upon field application. The results of the calculations showed that the intensity of the magnetoviscous response depends on the concentration and size of the large particles, and on the thickness of the surfactant layers.
本文报道了由分散在离子液体中的磁铁矿纳米粒子组成的磁性液体的制备。使用了不同的添加剂来稳定这些流体。通过磁沉降、离心和直接观察检查了胶体稳定性。这些测试的结果表明，只有当纳米粒子被一层与离子液体相容的表面活性剂包覆时，才能获得真正的铁磁流体。这些实验还表明，仅仅通过静电排斥是无法达到稳定性的。通过计算颗粒间相互作用的能量，验证了稳定性测试的结论。还研究了磁场作用下磁性液体的流变行为。通过微观结构模型对实验磁粘性响应进行了拟合。该模型认为，这些流体由两种粒子群组成，一种具有 9nm 的磁性核直径，另一种具有较大的直径。磁场作用下，假设会诱导出链状结构。根据估计，9nm 的粒子在磁场作用下太小而不会聚集。计算结果表明，磁粘性响应的强度取决于大颗粒的浓度、大小以及表面活性剂层的厚度。
