Collaborative Research: How magnetic nanoparticles organize in extreme force gradients

液体中的磁性纳米粒子可以点击在一起，制成微型搅拌棒，构建人工骨骼的支架，甚至可以捕获癌细胞并阻止其通过血液。为了实现这样的结构，人们必须了解控制这些粒子如何聚集在一起的力。该研究小组正在研究一种新的方法，用于在比自然发生的磁力大许多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。妇女和少数民族博士和本科生将被招募为这项工作，发生在两个物理系。在美国，物理学在所有学科的博士毕业生中女性和少数民族的比例最低，因此这一点至关重要。通过他们的密切互动，两个小组将设计一个30分钟长的磁性纳米粒子表演，包括视频和简单的演示，然后向学校团体表演。这个主题是非常直观的，所以学生将能够理解的结果和令人兴奋的应用，如药物输送，加热杀死癌症肿瘤，和芯片实验室的影响。最后，两位私人研究员会在本地的“科学咖啡厅”举办有关纳米科技的讲座，让市民可以参与讨论。技术摘要在纳米尺度上可以产生巨大的磁力梯度，并用于从流体中的磁性纳米颗粒形成几乎任何自组装形状。然而，在这些极端梯度中的组装显示出仍然无法解释的新行为，包括当向悬浮液中添加微量盐时产生的截然不同的结果。该项目旨在了解纳米颗粒周围的直接环境（离子，磁性，配体化学）如何影响其在极端力梯度下组装成几何排列的能力，这一理解可以改变纳米颗粒在现实世界中的应用方式和位置。该项目的具体目标集中在影响纳米颗粒组装的三个参数：（i）外部场梯度，（ii）胶体悬浮液的离子强度，和（iii）粒子间的磁相互作用。该研究小组正在将可控力-在纳米范围内以数量级变化-应用于纳米颗粒，因为它们的胶体环境被修改，其中一种变革性的方法涉及浸没在液体中的磁记录介质。通过观察纳米颗粒自组装成衍射光栅，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件，这些参数进行了研究。这些实验与理论计算和朗之万动力学模拟密切相关，后者解释了纳米级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、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知识价值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.