RUI: Systematic Study of the Rheology and Sedimentation of Microwire-Based Magnetorheological Fluids

CBET-0755696Bell传统磁流变液由悬浮在载液中的球形微米级铁磁颗粒组成。在磁场的作用下，这些悬浮液从粘性液体转变为半固态。通过改变外加磁场的强度来控制悬浮液的粘度和表观屈服应力。然而，在许多应用中，通常使用这些复合材料的一个主要缺点是颗粒沉淀，这需要颗粒的重新分散，这会导致不利的长响应时间。目前用于限制沉淀的添加剂在可比磁场下会导致屈服应力减小。在这项研究中，PI研究了非传统微丝磁流变液的流变性、沉降性和磁性，这些流体使用的是长宽比从3到100的圆柱形颗粒，悬浮在硅油和含有球形和微丝颗粒混合物的二相悬浮液中。利用基于模板的电沉积，PI制备了直径在260到320 nm之间、长度在1到30微米之间的纯铁磁性微丝。对于不同的流体组成和磁场强度，剪切应力将作为剪切速率的函数进行测量，并使用各种本构模型模拟结果，以确定作为这些微丝悬浮液的体积分数和颗粒几何形状和组成增加的函数的表观屈服应力、粘度和其他粘弹性性质。一个有限元多物理模拟程序包将构建这些悬浮液的基本模拟，以考察颗粒形状、长径比、磁性和颗粒浓度对这些悬浮液的沉积和磁流变学的影响。建立微丝悬浮液的磁流变学将是理解和应用磁流变液的重要一步。初步研究是有希望的；与传统的磁流变液相比，纯微丝磁流变液的沉降量显著减少，当只有很少的体积百分比的球体被微丝取代时。这些研究的更广泛影响是双重的。首先，将提供一种新型磁流变液的性质，其在保持更高的屈服应力的同时表现出减少的沉积。这一知识将有可能扩大磁流变液的应用范围，为各种新的应用铺平道路，这些应用可以直接转移到工业部门。从这些研究中获得的关于导线磁性的知识也可能在磁光和微波器件等应用中被证明是有用的。其次，该项目将为本科生和高中生提供培训和发展，促进教师的专业发展，并鼓励属于科学界代表性不足群体的个人参与。本科生将获得丰富的经验和培训，因为他们完全参与了MR流体的合成、表征、测试和建模以及结果的传播。由于这项工作涉及宾夕法尼亚州立大学和马里兰大学材料研究所(MRI)的合作者，我们的本科生研究人员将有机会与这些机构的其他学生和教职员工进行交流。

CBET-0755696BellConventional magnetorheological (MR) fluids consist of spherical micron-sized ferromagnetic particles suspended in a carrier fluid. These suspensions are converted from a viscous liquid to a semi-solid with the application of a magnetic field. The viscosity and apparent yield stress of the suspensions are controlled by varying the strength of the external magnetic field. However, a major drawback to common use of these composite materials in many applications is particle sedimentation that requires re-dispersion of the particles, which causes unfavorably lengthy response times. Current additives meant to limit sedimentation result in a diminished yield stress at comparable magnetic fields. In this study, The PIs investigate the rheology, sedimentation, and magnetic properties of unconventional microwire-based MR fluids employing cylindrical particles with aspect ratios ranging from 3 to 100 suspended in silicone oil and dimorphic suspensions that contain a mixture of spherical and microwire particles. Using template-based electrodeposition, The PIs fabricate pure ferromagnetic microwires with controllable diameters ranging from 260 to 320 nm and lengths in the range of 1 to 30 microns. For a variety of fluid compositions and magnetic field strengths, the shear stress will be measured as a function of shear rate and the results modeled using various constitutive models to determine the apparent yield stress, viscosity and other viscoelastic properties as a function of increasing volume fraction and particle geometry and composition of these microwire-based suspensions. A finite-element, multiphysics simulation package will construct basic simulations of these suspensions to examine the role of particle shape, aspect ratio, magnetic properties, and particle concentration on the sedimentation and magnetorheology of these suspensions. Establishing the magnetorheology of microwire suspensions will be a significant move forward in the understanding and application of MR fluids. Preliminary studies are promising; pure microwire MR fluids display a significantly decreased amount of settling as compared to conventional MR fluids when only a few volume percent of the spheres are replaced with microwires. The broader impact of these studies is twofold. First, properties of a novel magnetorheological fluid that displays reduced sedimentation while maintaining enhanced yield stress will be provided. This knowledge will have the potential to broaden the application of MR fluids, paving the way for a variety of new applications that could be transferred to the industrial sector directly. The knowledge about the magnetic properties of the wires gained from these studies may also prove useful in applications such as magneto-optical and microwave devices. Second, this project will provide for training and development of undergraduate and high school students, promote the professional development of faculty, and encourage participation by individuals belonging to groups underrepresented in the sciences. Undergraduate students will receive significant experience and training as they fully participate in the synthesis, characterization, testing, and modeling of the MR fluids and the dissemination of results. Since the work involves collaborators at the Materials Research Institute (MRI) at Penn State and at the University of Maryland, our undergraduate researchers will have the opportunity to communicate with other students and faculty at these institutions.