Dynamics of Magnetic NanoProbes in Polymer Melts

我们提出通过测量磁性纳米探针（MNPs）对振荡磁场的响应来系统地研究聚合物熔体中纳米颗粒的动力学。研究了纳米颗粒核尺寸、接枝分子量、接枝密度、熔体分子量、熔体聚合物旋转半径和熔体纠缠长度等因素的影响。这些实验将为文献中关于聚合物熔体中小颗粒动力学的各种先进理论提供明确的测试。在二氧化硅基体中制备由钴铁氧体纳米颗粒组成的MNPs，其核心尺寸在10-500 nm范围内可选择，尺寸分布窄，接枝聚合物的分子量和接枝密度可选择，以及永久嵌入偶极子，使纳米颗粒通过物理旋转响应振荡磁场。MNPs将通过扫描和透射电子显微镜，动态光散射和SQUID磁强计相结合来表征。然后将MNPs分散在聚异丁烯、聚二甲基硅氧烷和聚乙二醇的聚合物熔体中，并研究MNPs在这些熔体中的稳定性。稳定悬浮液将用于交流磁化率测量，其中施加振荡磁场，磁性纳米颗粒的响应提供了纳米颗粒旋转扩散系数的直接测量。反过来，这将使我们能够计算颗粒的旋转阻力，从而计算出所谓的纳米粘度，这将与通过流变测量获得的宏观粘度进行系统的比较。通过研究MNP尺寸、接枝分子量和接枝密度对纳米黏度和宏观黏度偏离的临界熔体分子量的影响，我们将确定它们对聚合物熔体中纳米颗粒动力学的影响，特别强调Stokes - Einstein关系的破坏和熔融聚合物与接枝聚合物的脱湿现象。这些实验将通过测量荧光MNPs在聚合物熔体中的平移扩散系数来补充，使用光漂白后荧光恢复技术（FRAP）。比较纳米颗粒的旋转和平移扩散的结果将为纳米颗粒在聚合物熔体中的动力学提供更深入的了解。对比匹配小角中子散射（SANS）可以直接观察聚合物熔体是否对接枝到纳米粒子上的聚合物进行脱水，这将与纳米粒子的动力学测量相关联。教育和外联活动的目的是增加代表性不足的群体参与科学和工程，并向广泛的受众传播拟议的研究结果。通过初高中材料科学与工程俱乐部的指导，大学预科的西班牙裔学生将被激励去攻读科学和工程学位。PI将访问西班牙裔学生比例较高的大学，并与西班牙裔专业工程师协会学生分会的成员会面，以激励他们攻读工程方面的高级学位，并从事研究和学术工作。将开发关于纳米粒子和复杂流体的基于网络的教育模块，并通过纳米中心广泛传播。知识价值：该活动的知识价值主要在于利用MNPs进行交流磁化率测量的变革潜力，为复杂流体中纳米颗粒的旋转动力学提供了新的和独特的见解。特别是，所提出的系统实验将阐明裸纳米粒子和聚合物接枝纳米粒子在聚合物熔体中的动力学。此外，将开发方法来生产由二氧化硅基体中的氧化铁核组成的复合纳米颗粒，具有可选择的尺寸和接枝聚合物。这些粒子的应用可以超越本文提出的特定研究任务，例如在其他复杂流体中类似的纳米粘度测量，或在生物医学领域作为MRI造影剂，或在振荡磁场中通过磁性纳米颗粒引起的热疗来治疗癌症。更广泛的影响：通过在定期审查机制进行拟议的研究，来自代表性不足群体的学生的参与和教育将大大加强。upm的化学工程系为650多名西班牙裔本科生提供服务，其中70%是女性。该系也在发展能力，成为美国西班牙裔博士的重要贡献者。该项目将支持2名研究生和46名本科生，他们很可能是西班牙裔，他们将参与纳米颗粒和复杂流体的激动人心的变革性研究。通过与车轮上的科学教育中心和美国国家科学基金会资助的威斯康星波多黎各材料和纳米生物医学和能源驱动系统与应用研究与教育合作伙伴关系的合作，拟议的K-12外展活动将覆盖数千名西班牙裔大学预科学生。该项目还将通过访问西班牙裔专业工程师协会的学生分会，影响全国的西班牙裔工程学院学生。

We propose to systematically study the dynamics of nanoparticles in polymer melts by measuring the response of magnetic nanoprobes (MNPs) to oscillating magnetic fields. The effects of nanoparticle core size, graft molecular weight, graft density, melt molecular weight, melt polymer radius of gyration, and melt entanglement length will be elucidated. These experiments will provide definitive tests of various theories advanced in the literature regarding the dynamics of small particles in polymer melts. Methods will be developed to produce MNPs consisting of cobalt ferrite nanoparticles in a silica matrix, with select able core size in the 10-500 nm range, narrow size distribution, grafted polymers of selectable molecular weight and graft density, and permanent embedded dipoles such that the nanoparticles respond to oscil lating magnetic fields by physical rotation. MNPs will be characterized through a combination of scanning and transmission electron microscopy, dynamic light scattering, and SQUID magnetometry. The MNPs will then be dispersed in polymer melts of poly(isobutylene), poly(dimethyl siloxane), and poly(ethylene glycol) and the stability of the MNPs in these melts will be studied. Stable suspensions will be used for AC susceptibility measurements, in which an oscillating magnetic field is applied and the response of the magnetic nanoparticles provides a direct measurement of the rotational diffusion coefficient of the nano-particles. This in turn will allow us to calculate the rotational drag on the particles and hence the so called nanoviscosity, which will be systematically compared to the macroviscosity obtained through rheological measurements. By studying the effect of MNP size, graft molecular weight, and graft density on the critical melt molecular weight for which the nanoviscosity and macroviscosity diverge we will determine their effect on the dynamics of the nanoparticles in polymer melts, with particular emphasis on the phenomena of breakdown of the Stokes Einstein relation and dewetting of the melt polymer from the graft polymer. These experiments will be complemented by measurements of the translational diffusion coefficient of fluorescent MNPs in polymer melts, using the technique of Fluorescence Recovery After Photobleaching (FRAP). Comparing results for rotational and translational diffusion of the nanoparticles will provide deeper insight into the dynamics of nanoparticles in polymer melts. Contrast matched Small Angle Neutron Scattering (SANS) will be applied to directly observe if the melt polymer dewets the polymer grafted to the nanoparticles, and this will be correlated to the measurements of nanoparticle dynamics. Education and outreach activities are aimed at increasing participation of underrepresented groups in Science and Engineering and disseminating the results of the proposed research to a wide audience. Pre-college Hispanic students will be motivated to pursue science and engineering degrees through mentoring of Middle and High School Materials Science and Engineering clubs. The PI will visit universities with high proportions of Hispanic students and meet with members of their Society of Hispanic Professional Engineers student chapters to motivate them to pursue advanced degrees in engineering and careers in research and academia. Web based educational modules on nanoparticles and complex fluids will be developed and widely disseminated through the NanoHub. Intellectual Merit: The intellectual merit of the proposed activity lies primarily in the transformative potential of the proposed AC susceptibility measurements using MNPs to provide new and unique insight into the rotational dynamics of nanoparticles in complex fluids. In particular, the proposed systematic experiments will elucidate the dynamics of bare and polymer grafted nanoparticles in polymer melts. Additionally, methods will be developed to produce composite nanoparticles consisting of iron oxide cores in a silica matrix, with selectable size and grafted polymers. Such particles could find applications beyond the specific research tasks proposed here, such as in similar nanoviscosity measurements in other complex fluids, or in the biomedical field as MRI contrast agents or in the treatment of cancer through hyperthermia induced by magnetic nanoparticles in oscillating magnetic fields. Broader Impact: By carrying out the proposed research at the UPRM, the participation and education of students from underrepresented groups will be significantly enhanced. The Chemical Engineering Department at UPRM serves over 650 Hispanic undergraduate students, 70% of which are female. The department is also developing capacity to become a significant contributor of Hispanic PhDs in the USA. This project will support 2 graduate students and 46 undergraduate students, most likely of Hispanic origin, who will participate in exciting, transformative research with nanoparticles and complex fluids. By partnering with the Science on Wheels Educational Center and the NSF funded Wisconsin Puerto Rico Partnership for Research and Education in Materials and Nanotechnology Center for Biomedical and Energy Driven Systems and Applications at UPRM the proposed K-12 outreach activities will reach thousands of Hispanic pre-college students. The project will also impact Hispanic engineering college students throughout the nation through the proposed visits to student chapters of the Society of Hispanic Professional Engineers.