Dynamics of Magnetic NanoProbes in Polymer Melts

我们建议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粒子的动力学。研究了纳米粒子核尺寸、接枝相对分子质量、接枝密度、熔体相对分子质量、熔体聚合物回转半径和熔体缠绕长度对聚合物性能的影响。这些实验将为文献中提出的关于聚合物熔体中小颗粒动力学的各种理论提供明确的测试。将开发一种方法来制备由二氧化硅基质中的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，尺寸分布窄，接枝聚合物的相对分子质量和接枝密度可选，以及永久嵌入的偶极，使纳米颗粒通过物理旋转对摆动的磁场做出响应。MNPs将通过扫描和透射电子显微镜、动态光散射和SQUID磁测量相结合来表征。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。稳定的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。这将使我们能够计算颗粒上的旋转阻力，从而计算出所谓的纳米粘度，它将被系统地与通过流变学测量获得的宏观粘度进行比较。通过研究MNP尺寸、接枝分子量和接枝密度对纳米粘度和宏观粘度发散的临界熔体分子量的影响，确定它们对聚合物熔体中纳米粒子动力学的影响，特别是斯托克斯-爱因斯坦关系的破裂和熔体聚合物与接枝聚合物的脱湿现象。作为这些实验的补充，将使用光漂白后荧光恢复(FRAP)技术测量荧光MNPs在聚合物熔体中的平移扩散系数。比较纳米粒子的旋转扩散和平移扩散的结果将有助于更深入地了解纳米粒子在聚合物熔体中的动力学。对比度匹配小角中子散射(SANS)将被用来直接观察熔融聚合物是否将接枝到纳米粒子上的聚合物脱水，这将与纳米粒子动力学的测量相关联。教育和外联活动的目的是增加科学和工程方面代表性不足的群体的参与，并向广大受众传播拟议研究的结果。通过初中和高中材料科学和工程俱乐部的指导，西班牙裔预科学生将被激励攻读科学和工程学位。PI将访问拉美裔学生比例较高的大学，并会见拉美裔专业工程师协会学生分会的成员，以激励他们攻读工程学高级学位以及研究和学术界的职业。将通过NanoHub开发和广泛传播关于纳米颗粒和复杂流体的基于网络的教育模块。智力价值：拟议活动的智力价值主要在于拟议的交流磁化率测量的转化潜力，该测量使用MNPs来提供对复杂流体中纳米颗粒旋转动力学的新的独特见解。特别是，拟议的系统实验将阐明裸露和聚合物接枝纳米颗粒在聚合物熔体中的动力学。此外，还将开发生产复合纳米颗粒的方法，这些纳米颗粒由二氧化硅基质中的氧化铁核心组成，具有可选的尺寸和接枝聚合物。这些粒子可以在这里提出的特定研究任务之外找到应用，例如在其他复杂流体中进行类似的纳米粘度测量，或者在生物医学领域作为磁共振造影剂，或者通过磁性纳米粒子在振荡磁场中诱导的热疗来治疗癌症。更广泛的影响：通过在UPRM开展拟议的研究，来自代表性不足群体的学生的参与和教育将得到显著加强。UPRM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。该系还在发展能力，以成为美国拉美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，他们最有可能是西班牙裔，他们将参与使用纳米颗粒和复杂流体进行令人兴奋的变革性研究。通过与轮子科学教育中心和NSF资助的威斯康星州波多黎各材料研究和教育伙伴关系以及UPRM生物医学和能源驱动系统和应用的纳米技术中心合作，拟议的K-12外联活动将覆盖数千名西班牙裔大学预科学生。该项目还将通过建议访问拉美裔专业工程师协会的学生分会，影响全国的拉美裔工程学院学生。

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.