GOALI Collaborative Research: Engineering magnetorheological fluids by controlling nonmagnetic particle interactions

磁流变（MR）流体是可磁化颗粒的悬浮液，其流变性能在外加磁场的作用下发生显著且可逆的改变。这些材料可以用于各种应用，目前的注意力主要集中在汽车设备上（例如，主动阻尼系统和离合器）。应用程序可以提高车辆质量（例如，行驶和操控）以及提高车辆的汽油里程。过去的研究表明，磁流变液的场致行为在很大程度上可以用静磁力及其与水动力的竞争来解释。然而，MR流体的应用需要某些与设备相关的其他特性，如非状态粘度、沉降、再分散性和耐久性。这些性质受到粒子间力而不是磁力的强烈影响。因此，很明显，为设备设计磁流变液需要了解各种粒子间力与悬浮液宏观性质之间的关系。在这项工作中，我们将使用几种互补的方法来探索粒子间力与宏观行为之间的关系，并研究观察到的行为的机制。通过在铁表面接枝不同的物种，可以改变铁表面之间的非磁性力。接枝层对颗粒间力的影响将直接使用胶体探针显微镜来确定，其中将测量正常和侧向（即摩擦）。接枝层对宏观流变性能的影响也将通过实验来确定。最后，我们将使用粒子级模拟来检查粒子间力的变化如何影响宏观行为。这将使我们能够确定在表面上由接枝物种引起的测量粒子间力的变化是否可以解释观察到的宏观性质的变化。知识价值。所提出的研究将提供关于MR流体性质的新信息，并提高我们优化流体和各种应用所需颗粒涂层的能力。这项工作也将更广泛地提高我们对颗粒凝胶的理解，因为我们将研究具有更深吸引力井深的系统，具有更大颗粒的系统，并探测比通常研究的更大的变形流变特性。更广泛的影响。该项目的资金将用于支持研究生，他们将在新兴的磁流变学领域，以及胶体探针显微镜和更一般的胶体凝胶和悬浮流变学领域进行培训。学生们还将通过与通用汽车公司的互动接触到他们的工作的工业应用。我们小组每年也会有本科生参与研究，因此我们也会在整个项目过程中培养一批MR、悬浮流变学和胶体科学方面的本科生。这些专业人员参与了其他教育项目，这些项目将从拟议的工作中受益。Klingenberg co教授的大一课程“社会概论”是工程学的重大挑战，这门课程研究了社会上的重大挑战是如何需要工程师来解决的。本课程的目标是招收新的学生进入工程领域，并招收和保留更大比例的女性。社会面临的主要挑战之一是能源可持续性。许多磁共振技术的应用是由汽车的能源经济驱动的，因此被纳入大挑战课程，以说明当前的研究活动是如何解决社会挑战的。在过去的6年里，Zauscher一直参与一个REU项目，该项目为来自加劳德特大学的听力受损学生提供实验室体验。我们建议每年夏天聘请一名这样的学生参与CPM测量。

0932680/0932715Klingenberg/ZauscherMagnetorheological (MR) fluids are suspensions of magnetizable particles, whose rheological properties can be dramatically and reversibly altered by applied magnetic fields. These materials can be exploited in a variety of applications, with much of the current attention focused on automotive devices (e.g., active damping systems and clutches). Applications can improve vehicle quality (e.g., ride and handling) as well as improve the gas mileage of vehicles. Past research has illustrated that the field induced behavior of MR fluids can be explained largely in terms of magnetostatic forces and their competition with hydrodynamic forces. However, applications of MR fluids demand certain device dependent characteristics of other properties, such as off state viscosity, sedimentation, redispersability, and durability. These properties are strongly influenced by interparticle forces other than magnetic forces. It is thus apparent that designing MR fluids for devices requires an understanding of the relationships between various interparticle forces and macroscopic properties of the suspensions. In the proposed work, we will use several complementary approaches to probe the relationships between interparticle forces and macroscopic behavior, and to investigate the mechanisms for observed behavior. Nonmagnetic forces between iron surfaces will be altered by grafting various species to the surfaces. The impact of the grafted layers on interparticle forces will be determined directly using colloidal probe microscopy, in which both the normal and lateral (i.e., friction) will be measured. The effects of the grafted layers on the macroscopic rheological properties will also be determined experimentally. Finally, we will use particle level simulations to examine how changes in interparticle forces affect macroscopic behavior. This will allow us to determine if changes observed in the measured interparticle forces caused by grafting species on the surfaces can account for the observed changes in macroscopic properties.Intellectual merit. The proposed research will provide new information about the properties of MR fluids, and improve our ability to optimize fluids and requisite particle coatings for various applications. This work will also more generally improve our understanding of particulate gels, as we will be investigating systems with deeper attractive well depths, systems with larger particles, and probing larger deformation rheological properties than typically studied.Broader impact. Funding for this project will be used to support graduate students, who will be trained in the emerging field of magnetorheology, as well as colloidal probe microscopy and the more general fields of colloidal gels and suspension rheology. The students will also be exposed to industrial applications of their work through interactions with General Motors. Our groups also involve undergraduate students in research every year, and thus we will also be training a stream of undergraduates in aspects of MR, suspension rheology, and colloid science throughout the course of this project. The PIs are involved in other education projects that will benefit from the proposed work. Klingenberg co teaches the freshman course "Introduction to Society" is Engineering Grand Challenges, which examines how society is significant challenges will require engineers to solve them. The goals of this course are to recruit new students into engineering, and to recruit and retain a larger fraction of women. One of society's main challenges is energy sustainability. Numerous applications of MR technology are motivated by energy economy in vehicles, and thus are incorporated into the Grand Challenges course to illustrate how current research activities are addressing society's challenges. Zauscher has been involved over the last 6 years in an REU program that provides laboratory experiences for hearing impaired students from Gallaudet University. We propose to engage one such student each summer in the CPM measurements.