The Role of Grafting Mechanism on the Self-Assembly and Properties of Polymer Nanocomposites

非技术摘要：将无机纳米颗粒(NPs)添加到聚合物(即塑料材料)中可以得到具有极高性能的杂化材料。一个经典的例子是，虽然橡胶(例如橡皮擦中的橡胶)的耐磨性极差，但添加二氧化硅纳米颗粒会使耐磨性大大提高，以至于汽车可以使用超过50,000英里的轮胎行驶。虽然这种性能的改善推动了聚合物纳米复合材料领域的发展，但固有的问题是，纳米颗粒在化学上与聚合物(一种碳氢材料)非常不同，因此有很强的相互分离的趋势，类似于水-油悬浮液。因此，只有通过聚合物和NPs的紧密混合才能实现的期望的、有利的性能改善在常规基础上变得很难实现。这里的工作建议通过在纳米粒子上化学接枝高聚物链来解决这个问题，这样无机粒子表面就可以与聚合物“屏蔽”，从而获得相容性。特别是，这项工作侧重于这种嫁接的两种策略：要么将完全形成的链嫁接到表面，要么从表面逐段生长链。这些策略中哪一种可以更好地控制粒子-聚合物的相容性，从而最大限度地改善性能是本研究的重点。除了这一技术重点，拟议的工作还将强调对学生的广泛、跨学科的教育，以及通过吸引高中生和本科生参加PI实验室的工程研究活动，招募和留住女性和少数族裔学生参加STEM项目。技术摘要：这项建议的重点是聚合物接枝纳米颗粒(NP)在聚合物基质中的自组装，目的是影响所产生的杂化(或复合材料)材料的行为。这种物理状况与橡胶轮胎和环氧树脂(用于电子封装和计算机芯片应用)的性能改进有关。通过三个试验台的探索，巧妙地将理论和实验相结合，来研究这一支撑问题。特别是，将强调链嫁接到NP表面的机制对最终材料性质的作用，即链是否预先成形并附着在表面上，或者链是否从表面逐个生长。预计前一种机理将在NP表面产生更均匀的聚合物覆盖。表面覆盖率的这些差异对形成的组件和由此产生的性能的影响是这项工作的最终重点。这些研究活动与广泛的教育和外联活动相结合。一个主要的重点将是在本科生和研究生阶段招收代表性不足的学生(包括妇女和少数族裔)。目前的暑期高中研究计划和本科生研究体验计划都计划在学年期间增加，目标是招募(并希望留住)女性和少数族裔加入STEM努力。

NON-TECHNICAL SUMMARY: The addition of inorganic nanoparticles (NPs) to a polymer (i.e. a plastic material) can result in hybrid materials with highly improved properties. A classic example is that, while rubber (as e.g. in an eraser) has extremely poor wear resistance, the addition of silica nanoparticles causes the wear resistance to go up so much that a car can drive with tires that last over 50,000 miles. While such property improvements are what drive developments in the field of polymer nanocomposites, the inherent problem is that the nanoparticles are chemically so different from the polymer (a hydrocarbon material) and thus have a strong tendency to separate from each other akin to a water-oil suspension. Thus, the desirable, favorable property improvements that can only be realized by the intimate mixing of the polymer and the NPs become hard to realize on a routine basis. The work here proposes to remedy this problem by chemically grafting polymer chains onto the NPs so that the inorganic particle surface can be "shielded" from the polymer, thus allowing miscibility to be obtained. In particular, the work focuses on two strategies for this grafting: either grafting fully formed chains to the surfaces, or growing the chains piece-by-piece from the surface. Which of these strategies allows better control over particle-polymer miscibility and therefore improve properties the most is the focus of this research. In addition to this technical emphasis, the proposed work will also stress the broad, interdisciplinary education of students and the recruitment and retention of women and minority students into STEM programs by attracting high-school and undergraduate students into engineering research activities in the PI's laboratory.TECHNICAL SUMMARY: The focus of this proposal is on the self-assembly of polymer-grafted nanoparticles (NPs) in a polymer matrix with the goal of impacting the behavior of the resulting hybrid (or composite) material. This physical situation has relevance to improved performance in, for example, rubber tires and epoxies (which are used in electronic packaging and computer chip applications). This underpinning question will be studied through the exploration of three test-beds by judiciously combining theory and experiments. In particular, emphasis will be placed on role of the mechanism by which chains are grafted onto NP surfaces on the final material properties, i.e., whether the chains are preformed and attached to the surface or if the chains are grown link-by-link from the surface. It is expected that the former mechanism will yield a more uniform polymer coverage on the NP surface. The consequence of these differences in surface coverage on the assemblies formed and the resulting properties is the ultimate focus of this work. These research activities are coupled to extensive education and outreach activities. A major focus will be to recruit underrepresented students (both women and minorities) at both the undergraduate and graduate levels. It is planned to grow both the current summer high-school research program, and also the research-experiences-for-undergraduates program during the schoolyear, with the goal of recruiting (and hopefully retaining) women and minorities into STEM efforts.