RUI: Multi-scale modeling of interfacial flows of magnetic fluids with macro-chain aggregates

磁性流体(或称磁流体)是磁性纳米颗粒的悬浮体，其性质和流动受到外加磁场的影响，因此在工业和生物医学应用中非常有用。未来的潜在应用，如靶向给药和微流控泵，涉及到活跃的界面和小尺度上的运动，在这些运动中，磁性粒子的分布可能变得不均匀。特别是，在中等电场下，纳米颗粒聚集成宏观链，进而影响流体流动。研究人员此前曾使用在阿贡国家实验室获得的高分辨率X射线相衬图像观察到这些链。在小尺度的磁流体建模和模拟方面的进一步进展需要新的方法。为了加快铁流器件的开发和设计步伐，促进新的铁磁流体应用的探索，需要一种健壮和灵活的模拟方法。该项目将以多尺度代码的形式开发、验证和应用这种工具，用于磁性流体界面流动的数值模拟。这些模拟程序将场致宏观磁粒子链的介观模型和块体磁流体的实际非线性磁化强度与最先进的界面Navier-Stokes程序相结合。Navier-Stokes计算将包括一个高阶曲率算法，该算法可以准确地计算界面上的表面张力。场诱导大分子链产生的粘性应力将从耗散粒子动力学模型中得到。该提案包括精心计划的项目，这些项目将吸引和支持蒙特克莱尔州不同人群的学生进行前沿研究。调查人员将开发一种计算机模拟磁性液体，也被称为磁流体，这是一种独特的“智能”材料，可以很容易地使用普通磁铁操纵。虽然在计算机磁盘驱动器中广泛用作液体密封，但这种易于控制的液体具有更大的潜力，包括应用于生物医学(药物输送、眼科手术和核磁共振造影剂)以及用于生物技术和药物测试的操纵微小液体体积的小型设备。进展因两个障碍而停滞不前。首先，实验受到限制，因为这种液体非常不透明，看起来像是一种闪亮的黑色液体。其次，纳米粒子赋予了流体的磁性，也导致了内部结构，如粒子链，这使得其数学描述变得复杂。该项目通过使用最先进的计算机模拟而不是实验克服了第一个挑战，而通过在阿贡国家实验室进行的高分辨率x射线实验建立内部结构的简单机械模型来克服第二个挑战。研究人员将让学生在这种计算机模拟工具的开发中发挥关键作用，该工具可用于探索、设计和测试磁性液体的这些和其他新应用。

Magnetic fluids (or ferrofluids) are suspensions of magnetic nanoparticles whose properties and flows are affected by applied magnetic fields, making them useful in industrial and biomedical applications. Potential future applications, such as targeted drug delivery and micro fluidic pumping, involve both active interfaces and motion on small scales, upon which the magnetic particle distribution may become nonuniform. In particular, under moderate fields, nanoparticles aggregate into macroscopic chains which, in turn, affect the fluid flow. These chains have been previously observed by the investigators using high resolution X-ray phase-contrast images obtained at Argonne national lab. Further progress in modeling and simulation of ferrofluids on small scales demands new approaches. To speed the pace of development and design of ferrofluidic devices and to facilitate the exploration of new ferrofluid applications, a robust and exible simulation method is required. This project will develop, validate and apply such a tool, in the form of a multi-scale code for the numerical simulation of interfacial flows of magnetic fluids. These simulation codes will integrate a mesoscale model of field-induced macroscopic magnetic-particle chains and a realistic nonlinear magnetization for the bulk ferrofluid with a state-of-the-art interfacial Navier-Stokes code. The Navier-Stokes computation will include a high-order curvature algorithm that accurately computes surface tension at interfaces. Viscous stress due to field induced macro-chains will be derived from a dissipative particle dynamics type model. The proposal includes carefully planned projects that will involve and support students from Montclair State's diverse population in leading-edge research.The investigators will develop a computer simulation of magnetic liquid, also known as ferrofluid, a unique "smart" material that is easily manipulated using ordinary magnets. While widely used as a liquid seal in computer disk drives, this easily controlled fluid has far greater potential, including applications in biomedicine (drug delivery, eye surgery and as MRI contrast agents) and in small scale devices which manipulate tiny fluid volumes, as used in biotechnology and pharmaceuticals tests. Progress has been stalled by two obstacles. First, experiments are limited because the fluid is very opaque, appearing as a shiny black liquid. Second, the nano-scale particles which give the fluid its magnetic character also lead to internal structures, such as particle chains, which make its mathematical description complex. This project overcomes the first challenge by using state-of-the-art computer simulations instead of experiments, while it overcomes the second challenge by building simple mechanical models of internal structure based on high resolution x-ray experiments, performed at Argonne national lab. The investigators will involve students in key roles in the development of this computer simulation tool that can be used to explore, design and test these and other new applications of magnetic fluids.