Experimental studies and computational simulations of the anisotropy of the magnetoviscous effect in ferrofluids

本研究计画旨在利用狭缝式黏度计进行实验研究，以探讨磁流体之磁黏滞效应之各向异性。在该项目的前一部分中，选择并表征了合适的铁磁流体，并建立了一个狭缝式粘度计，可以测量所有三个粘度系数，这意味着磁场方向为流动方向或剪切梯度或中性方向，而不会受到Rosensweig不稳定性的干扰。一个特殊的磁线圈系统提供了一个非常强大的和均匀的磁场，使铁磁流体与强粒子间相互作用和弱粒子间相互作用的铁磁流体可以研究。在前一阶段进行的实验中，可以表明，弱相互作用流体和强相互作用流体之间关于磁粘效应及其各向异性存在显着差异。粘性系数的变化及其与磁场强度和所施加的机械载荷的关系可以根据磁性颗粒的结构形成来解释。此外，一个实验台的合成颗粒的新泰勒制造的单和双分散的铁磁流体使用超声气溶胶热解过程已建成和测试。计划在最后一个项目阶段使用相应的流体。在项目的最后阶段，计划进行专门的实验，以证明所观察到的磁粘效应的微观假设，并将其与流体的微观结构联系起来。因此，将采用含有不同尺寸的颗粒（因此具有不同的颗粒间相互作用）的铁磁流体、双分散颗粒混合物或棒状模型颗粒。

The research project aims to investigate the anisotropy of the magnetoviscous effect in ferrofluids by experimental studies using a slit die viscometer. In the previous part of the project, suitable ferrofluids were selected and characterized and a slit die viscometer was built that allows measurements of all three viscosity coefficients, meaning for a magnetic field oriented in the direction of the flow or the shear gradient or in the neutral direction, without Rosensweig instabilities interfering. A special magnetic coil system provides a notably strong and homogeneous magnetic field so that both ferrofluids with strong interparticle interactions and ferrofluids with weak interparticle interactions could be studied. In the experiments undertaken in the previous phase it could be shown, that significant differences between weakly and strong interacting fluids concerning the magnetoviscous effect and its anisotropy exist. Change in the viscosity coefficients and their relations depending on field strength and mechanical load applied could be explained on the basis of structure formation of the magnetic particles. Moreover a test-rig for the synthesis of particles for new taylor-made mono- and bidisperse ferrofluids using an ultrasonic aerosol pyrolysis process has been build up and tested. Respective fluids are planned to be used in the last project phase. For the final project phase dedicated experiments are planned to prove the microscopic hypotheses for the observed magnetoviscous effects and to relate them to the microstructure of the fluids. Therefore ferrofluids containing differently sized particles - having thus different interparticle interaction -, bidisperse particle mixtures or rod like model particles will be employed.