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

CBET-0755696贝尔传统的磁流变（MR）流体由悬浮在载液中的球形微米级铁磁颗粒组成。这些悬浮液通过施加磁场从粘性液体转化为半固体。悬浮液的粘度和表观屈服应力通过改变外部磁场的强度来控制。然而，在许多应用中通常使用这些复合材料的主要缺点是颗粒沉降，其需要颗粒的再分散，这导致不利地过长的响应时间。目前用于限制沉降的添加剂在相当的磁场下导致屈服应力减小。在这项研究中，PI调查的流变学，沉降，和非常规的基于微丝的MR流体采用圆柱形颗粒的纵横比范围从3到100悬浮在硅油和二态悬浮液，含有球形和微丝颗粒的混合物的磁性能。使用基于模板的电沉积，PI制造纯铁磁微丝，其直径范围为260至320 nm，长度范围为1至30微米。对于各种流体组成和磁场强度，剪切应力将被测量为剪切速率的函数，并且使用各种本构模型对结果进行建模，以确定表观屈服应力、粘度和其他粘弹性，作为这些基于微丝的悬浮液的增加的体积分数和颗粒几何形状和组成的函数。一个有限元，多物理场模拟包将构建这些悬浮液的基本模拟，以检查颗粒形状，纵横比，磁性和颗粒浓度对这些悬浮液的沉降和磁流变学的作用。建立微导线悬浮液的磁流变学将是对磁流变液的理解和应用的一个重大进展。初步研究是有希望的;当只有几个体积百分比的球体被微丝代替时，与常规MR流体相比，纯微丝MR流体显示出显著减少的沉降量。这些研究的广泛影响是双重的。首先，将提供一种新型磁流变流体的性质，其显示出减少的沉降同时保持增强的屈服应力。这些知识将有可能扩大磁流变液的应用，为直接转移到工业部门的各种新应用铺平道路。从这些研究中获得的关于线的磁特性的知识也可以证明在诸如磁光和微波器件的应用中是有用的。第二，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，并鼓励属于在科学领域代表性不足的群体的个人参与。本科生将获得重要的经验和培训，因为他们充分参与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材料研究所（MRI）和马里兰州大学的合作者，我们的本科研究人员将有机会与这些机构的其他学生和教师进行交流。

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.