Dynamics of Magnetic NanoProbes in Polymer Melts

我们建议通过测量磁性纳米探针（MNP）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。纳米粒子的核心尺寸，接枝分子量，接枝密度，熔体分子量，熔融聚合物的回转半径，和熔体缠结长度的影响将得到阐明。这些实验将提供明确的测试各种理论先进的文献中关于小颗粒在聚合物熔体中的动力学。将开发方法来生产由二氧化硅基质中的钴铁氧体纳米颗粒组成的MNP，其具有在10-500 nm范围内的可选择的核尺寸、窄的尺寸分布、可选择的分子量和接枝密度的接枝聚合物以及永久嵌入的偶极子，使得纳米颗粒通过物理旋转响应于振荡磁场。MNP将通过扫描和透射电子显微镜，动态光散射和SQUID磁强计的组合进行表征。然后将MNP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MNP在这些熔体中的稳定性。稳定的悬浮液将用于AC磁化率测量，其中施加振荡磁场，并且磁性纳米颗粒的响应提供纳米颗粒的旋转扩散系数的直接测量。这反过来将使我们能够计算颗粒上的旋转阻力，从而计算所谓的纳米粘度，将其与通过流变测量获得的宏观粘度进行系统地比较。通过研究MNP的尺寸，接枝分子量，接枝密度的临界熔体分子量的纳米粘度和宏观粘度发散的影响，我们将确定其对聚合物熔体中的纳米粒子的动力学的影响，特别强调的现象的斯托克斯-爱因斯坦关系和脱湿的熔融聚合物从接枝聚合物的故障。这些实验将通过测量聚合物熔体中荧光MNP的平移扩散系数来补充，使用光漂白后荧光恢复（FRAP）技术。比较结果的旋转和平移扩散的纳米粒子将提供更深入的了解聚合物熔体中的纳米粒子的动力学。对比度匹配的小角中子散射（SANS）将被应用于直接观察熔融聚合物是否使接枝到纳米颗粒上的聚合物去湿，并且这将与纳米颗粒动力学的测量相关联。教育和外联活动旨在增加科学和工程领域代表性不足的群体的参与，并向广大受众传播拟议研究的成果。大学预科西班牙裔学生将有动力通过初中和高中材料科学与工程俱乐部的指导，追求科学和工程学位。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学生分会的成员会面，以激励他们追求工程和研究和学术事业的高级学位。将通过NanoHub开发和广泛传播关于纳米粒子和复杂流体的网络教育模块。智力优势：拟议活动的智力价值主要在于拟议的交流磁化率测量的变革潜力，使用MNP提供新的和独特的洞察复杂流体中的纳米粒子的旋转动力学。特别是，拟议的系统实验将阐明裸和聚合物接枝纳米粒子在聚合物熔体中的动力学。此外，还将开发生产由二氧化硅基质中的氧化铁核组成的复合纳米颗粒的方法，这些纳米颗粒具有可选择的尺寸和接枝聚合物。这种粒子可以找到超出这里提出的具体研究任务的应用，例如在其他复杂流体中的类似纳米粘度测量，或在生物医学领域作为MRI造影剂，或通过在振荡磁场中由磁性纳米粒子诱导的热疗治疗癌症。更广泛的影响：通过在普审机制开展拟议的研究，将大大加强代表性不足群体学生的参与和教育。UPRM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。该部门还在发展能力，成为西班牙裔博士在美国的重要贡献者。该项目将支持2名研究生和46名本科生，最有可能是西班牙裔，他们将参与纳米粒子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州波多黎各合作伙伴关系的研究和教育材料和纳米技术中心的生物医学和能源驱动的系统和应用在UPRM的拟议K-12推广活动将达到数千名西班牙裔大学预科生。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，影响全国各地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.