Collaborative Research: How magnetic nanoparticles organize in extreme force gradients

非技术摘要流体中的磁性纳米颗粒可以点击组合在一起，制造微型搅拌棒，构建人造骨骼的支架，甚至是捕获癌细胞并阻止它们在血液中传播的屏障。要实现这种结构，必须了解控制这些粒子如何聚集在一起的力。研究小组正在研究一种新的方法，在比自然产生的磁力大许多个数量级的极端磁力下将纳米颗粒连接在一起。系统的实时实验和理论模拟进行了比较，以了解这些系统的新物理及其在纳米技术中的潜在应用。女性和少数族裔的博士和本科生将被招募参加这项在两个物理系内进行的工作。在美国，物理学是所有学科中女性比例最低的，毕业博士比例也是少数，因此这一点至关重要。通过他们的亲密互动，两个小组将设计一个30分钟长的带有视频和简单演示的磁性纳米粒子展示，然后向学校小组表演。这一主题非常直观，因此学生将能够理解结果及其对令人兴奋的应用的影响，如药物输送、加热杀灭癌症肿瘤和芯片实验室。最后，两位专业人士将在本地的“科学咖啡馆”讲解纳米科技，市民可在那里讨论科学。技术摘要无磁力梯度可以在纳米尺度上产生，并被用来从流体中的磁性纳米颗粒制造几乎任何自组装形状。然而，在这些极端梯度中的组装显示了仍然无法解释的新奇行为，包括在悬浮液中加入微量盐时，结果截然不同。该项目试图了解纳米粒子周围的环境(离子、磁性、配体化学)如何影响其在极力梯度下组装成几何排列的能力，这一理解可能会改变纳米粒子在现实世界应用中的使用方式和地点。该项目的具体目标集中在影响纳米颗粒组装的三个参数上：(I)外场梯度，(Ii)胶体悬浮液的离子强度，以及(Iii)颗粒间的磁性相互作用。随着纳米颗粒胶体环境的改变，研究团队正在对纳米颗粒施加可控的力--这种力的大小在纳米级之间变化--通过一种涉及浸入液体中的磁记录介质的变革性方法。这些参数是通过观察纳米颗粒自组装成衍射栅，以及通过执行扭矩混合磁共振光谱测量来研究少数纳米颗粒组装来研究的。这些实验与理论计算和朗之万动力学模拟密切相关，这些模拟解释了纳米尺度相互作用的变化如何改变它们产生的新兴自组装结构。多时间尺度的有限温度模拟允许在合理的计算时间内将预测的大型组件与实验进行比较。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Non-Technical AbstractMagnetic nanoparticles in fluids can click-together to make miniature stir sticks, scaffolds for building artificial bones, and even barriers to trap cancer cells and prevent their traveling through blood. To realize such structures, one must understand the forces that control how these particles come together. The research team is studying a novel method for connecting nanoparticles together under extreme magnetic forces that are many orders of magnitude larger than naturally occurring ones. Systematic real-time experiments and theoretical simulations are compared to understand the new physics of these systems and their potential applications in nanotechnology. Women and minority PhD and undergraduate students will be recruited for this work that takes place within two Physics departments. In the US, Physics has the lowest female and minority percentage of graduating PhDs of any discipline so this is of critical importance. Through their close interaction, the two groups will design a 30 minute long Magnetic Nanoparticle Show with videos and simple demonstrations, and then perform the show to school groups. This topic is very visual so students will be able to understand the results and the implications for exciting applications such as drug delivery, heating to kill cancer tumors, and lab-on-a-chip. Finally, the two PIs will give talks on nanotechnology at local "Science Cafes," where members of the public can come to discuss science. Technical AbstractMassive magnetic force gradients can be created at the nanoscale and used to make virtually any self-assembled shape from magnetic nanoparticles in fluids. However, assembly in these extreme gradients shows novel behaviors that remain unexplained, including vastly different results when a minute amount of salt is added to the suspending fluid. This project seeks to understand how the immediate environment surrounding a nanoparticle (ionic, magnetic, ligand chemistry) affects its ability to assemble into geometric arrangements in extreme force gradients, an understanding that could transform how and where nanoparticles can be used in real-world applications. The specific aims of this project focus on three parameters that affect nanoparticle assembly: (i) external field gradient, (ii) ionic strength of colloidal suspensions, and (iii) interparticle magnetic interactions. The research team is applying controllable forces - that vary by orders of magnitude over just nanometers - to nanoparticles as their colloidal environment is modified, with a transformative approach involving magnetic recording media submerged in liquid. These parameters are studied by observing nanoparticles self-assemble into a diffraction grating, as well as by performing torque-mixing magnetic resonance spectroscopy measurements to study few-nanoparticle assemblies. These experiments are closely tied with theoretical calculations and Langevin dynamics simulations that explain how changes in nanoscale interactions modify the emergent self-assembled structures they produce. Multi-timescale, finite-temperature simulations allow predicted large assemblies to be compared to experiments within reasonable computation times.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.